Converting a polycrystalline shell to single crystal in superalloys produced via additive manufacturing

Abstract

An additive manufacturing process to produce a three-dimensional printed part includes, spreading a layer of an unmelted metal powder on a powder bed, melting a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of the additively manufactured 3D printed part, repeating the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder, displacing, utilizing a tool, the unmelted metal powder adjacent to a first edge of the shape, re-melting the first edge, and repeating the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers of the additively manufactured 3D printed part are printed. Re-melting the first edge forms a second edge that is devoid of polycrystalline metal.

Description

CONVERTING A POLYCRYSTALLINE SHELL TO SINGLE CRYSTAL IN SUPERALLOYS PRODUCED VIA ADDITIVE MANUFACTURINGCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application for patent claims priority to and the benefit of provisional patent application number 63 / 615,581 entitled “Converting a Polycrystalline Shell To Single Crystal In Superalloys Produced Via Additive Manufacturing” filed in the United States Patent and Trademark Office on December 28, 2023, the entire content of which is incorporated herein by reference as if fully set forth below in its entirety and for all applicable purposes.TECHNICAL FIELD

[0002] Aspects described herein are generally related to additive manufacturing and more particularly related to converting a polycrystalline shell to single crystal in superalloys produced via additive manufacturing.BACKGROUND

[0003] Additive manufacturing of single crystals (SX) (sometimes called mono-crystal) using powder bed technologies such laser powder bed fusion and electron beam melting (EBM) may yield parts having a single crystal region bordered by a polycrystalline (PX) region. The polycrystalline region is undesirable. In some examples the polycrystalline region effectively forms a shell around the single crystal region. In some examples, the shell may have a thickness of about 1 to 2 mm. In some examples, unmelted metal powder in the powder bed around the edge of the single crystal region may act as a nucleation site for growth of the polycrystalline region.

[0004] Engineers and scientists may be addressing issues related to polycrystalline growth; however, effective methods of avoiding the polycrystalline shell, converting the polycrystalline shell to single crystal, or removing the polycrystalline shell (in situ) during additive manufacturing remain elusive.BRIEF SUMMARY

[0005] The following summary is provided to facilitate an understanding of some of the innovative features unique to the examples disclosed and is not intended to be a full description. A full appreciation of the various aspects of the examples can be gained by taking the entire specification, claims, drawings, and abstract as a whole.

[0006] In one example, a method of additively manufacturing a three-dimensional (3D) printed part is disclosed. The method includes spreading a layer of an unmelted metal powder on a powder bed, melting a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part, repeating the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder, displacing, utilizing a tool, the unmelted metal powder adjacent to a first edge of the shape, re-melting the first edge of the shape, and repeating the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers of the additively manufactured 3D printed part are printed.

[0007] In another example, an apparatus is disclosed. The apparatus includes means for spreading a layer of an unmelted metal powder on a powder bed, means for melting a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part, means for repeating the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder, means for displacing the unmelted metal powder adjacent to a first edge of the shape, means for re-melting the first edge of the shape, and means for repeating the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers of the additively manufactured 3D printed part are printed.

[0008] In another example a non-transitory computer-readable medium storing instructions that when executed by a processing circuit cause the processing circuit to perform various processes is disclosed. The various processes may be performed by various apparatus and / or tools. In this example the processing circuit is caused to cause an apparatus and / or tool to spread a layer of an unmelted metal powder on a powder bed, melt a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part, repeat the spreading and the melting of at least one of: a next layer of the unmeltedmetal powder, or a predetermined plurality of next layers of the unmelted metal powder, displace, utilizing the tool, the unmelted metal powder adjacent to a first edge of the shape, re-melt the first edge of the shape, and repeat the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers of the additively manufactured 3D printed part are printed.

[0009] In an additional example, an apparatus is disclosed. The apparatus includes a powder bed, an electron beam gun focused on the powder bed, a recoater head configured to recoat the powder bed with a layer of an unmelted metal powder, a tool actuator coupled to the recoater head, a tool coupled to the tool actuator, where the apparatus is configured to: spread, utilizing the recoater head, the layer of the unmelted metal powder on the powder bed, melt, utilizing the electron beam gun, a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part, repeat the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder, displace, utilizing the tool coupled to the tool actuator coupled to the recoater head, the unmelted metal powder adjacent to a first edge of the shape, re-melt, utilizing the electron beam gun, the first edge of the shape, and repeat the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers of the additively manufactured 3D printed part are printed.

[0010] In another example, a system is disclosed. The system includes one or more processors, one or more memories coupled to the one or more processors, a powder bed, an electron beam gun focused on the powder bed and coupled to the one or more processors, a recoater head coupled to the one or more processors, a tool actuator coupled to the recoater head and the one or more processors, a tool coupled to the tool actuator. In the examples the one or more processors are configured to, individually or collectively, based at least in part on information stored in the one or more memories: spread, utilizing the recoater head, a layer of an unmelted metal powder on the powder bed, melt, utilizing an electron beam emitted by the electron beam gun, a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part, repeat the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder, displace, utilizingthe tool coupled to the tool actuator coupled to the recoater head, the unmelted metal powder adjacent to a first edge of the shape, re-melt, utilizing the electron beam gun, the first edge of the shape, and repeat the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers of the additively manufactured 3D printed part are printed.

[0011] An additional example describes a method of additively manufacturing a three- dimensional (3D) printed part. The method includes fabricating, using an electron beam melting additive manufacturing process, the 3D printed part, removing the unmelted metal powder from exterior surfaces of the 3D printed part, and converting polycrystalline metal encasing the 3D printed part to single crystal metal.

[0012] An example describing a method of converting an outer polycrystalline shell of an additively manufactured three-dimensional (3D) printed part into a single crystal method is disclosed. In this example, the method includes securely receiving the additively manufactured 3D printed part, the part additively manufactured using an electron beam melting process, the part having a single crystal core (also referred to herein as a single crystal metal core) and the outer polycrystalline shell, removing unmelted metal powder from the outer polycrystalline shell, and applying heat to the outer polycrystalline shell to re-melt the outer polycrystalline shell, the re-melting converting the outer polycrystalline shell into the single crystal having a same orientation as the single crystal core.

[0013] Still another example of an apparatus is disclosed. In this example, the apparatus is configured to fabricate, utilizing additive manufacturing processes, a three- dimensional single crystal metal part as described herein and shown in the drawings.

[0014] These and other aspects will become more fully understood upon a review of the detailed description which follows. Other aspects, features, and examples will become apparent to those of ordinary skill in the art upon reviewing the following description of specific exemplary aspects in conjunction with the accompanying figures. While features may be discussed relative to certain examples and figures below, all examples can include one or more of the advantageous features discussed herein. In other words, while one or more examples may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various examples discussed herein. Similarly, while examples may be discussed below as device, system,or method examples, it should be understood that such examples can be implemented in various devices, systems, and methods.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying figures, in which like reference numerals refer to identical or functionally similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the examples and, together with the detailed description, serve to explain the aspects disclosed herein.

[0016] FIG. 1 is a conceptual block diagram with illustrations depicting two processes of surface re-melting of a polycrystalline shell according to some aspects of the disclosure.

[0017] FIG. 2 is a schematic of a suction device including a gas jet device coaxial to the suction device according to some aspects of the disclosure.

[0018] FIG. 3A is a schematic of a first displacement member that displaces unmelted metal powder from the edges of a first part during an additive manufacturing process according to some aspects of the disclosure.

[0019] FIG. 3B is a schematic of a second displacement member that displaces unmelted metal powder from the edges of a second part during an additive manufacturing process according to some aspects of the disclosure.

[0020] FIG. 4 is a schematic of a partial re-melting of a surface of a sample using a 2kW laser according to some aspects of the disclosure.

[0021] FIG. 5 is a photomicrograph of a sample of a part fabricated using an electron beam melting additive manufacturing process using a nickel-based superalloy according to some aspects of the disclosure.

[0022] FIG. 6 is a photomicrograph of the sample of FIG. 5 after being surface heat treated, the heat treatment converting the polycrystalline shell into a single crystal according to some aspects of the disclosure.

[0023] FIG. 7 is an image with an inset illustration of a pair of 3D printed metal products formed using an electron beam melting process according to some aspects of the disclosure.

[0024] FIG. 8 is a simplified, not-to-scale, artist’s rendition of a plurality of the uppermost layers of a cross-section of a sample of a metal product undergoing fabrication utilizing an electron beam melting additive manufacturing process according to some aspects of the disclosure.

[0025] FIG. 9 is a block diagram of an example of system that may be used to displace unmelted metal powder from edges of one or more additively manufactured printed layers of a 3D printed metal part during fabrication according to some aspects of the disclosure.

[0026] FIG. 10 is a flow chart illustrating an example process of metal 3D printing utilizing additive manufacturing and an electron beam melting process according to some aspects of the disclosure.

[0027] FIG. 11 is a flow chart illustrating an example process of metal 3D printing utilizing additive manufacturing and an electron beam melting process according to some aspects of the disclosure.

[0028] FIG. 12 illustrates one example of a process, alongside a cross-section of a first body and a cross-section of second body according to some aspects of the disclosure.DETAILED DESCRIPTION

[0029] The particular values and configurations discussed in the following non-limiting examples can be varied and are cited merely to illustrate one or more examples and are not intended to limit the scope thereof.

[0030] Examples will now be described more fully hereinafter with reference to the accompanying drawings. The examples disclosed herein can be modified within the scope of this disclosure and should not be construed as being limiting; rather, these examples are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to persons of ordinary skill in the art. Like numbers refer to like elements throughout.

[0031] The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to persons having ordinary skill in the art that these concepts may be practiced without these specific details. In some examples, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

[0032] The terminology used herein is for the purpose of describing particular examples only and is not intended to be limiting. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise” and / or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0033] Throughout the specification and claims, terms may have nuanced meanings suggested or implied in context beyond an explicitly stated meaning. Likewise, the phrase “in one example” as used herein does not necessarily refer to the same example and the phrase “in another example” as used herein does not necessarily refer to a different example. It is intended that the scope of disclosure may encompass subject matter of one or more examples in whole or in part.

[0034] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0035] It will be understood that particular examples described herein are shown by way of illustration and not as limitations. Aspects described herein can be employed in various examples without departing from the scope of the disclosure. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific aspects and procedures described herein. Such equivalents are considered to be within the scope of this disclosure and are covered by the claims.

[0036] The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and / or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and / or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and / or.” Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

[0037] As used in this specification and claim(s), the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0038] The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAG, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

[0039] As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c. As used herein, “or” is intended to be interpreted in the inclusive sense, unless otherwise explicitly indicated. For example, “a or b” may include a only, b only, or a combination of a and b. Similarly, a phrase referring to A and / or B may include A only, B only, or a combination of A and B (i.e., the 7’ character may be used to represent the word ‘or’).

[0040] All of the aspects disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the aspects have been described in terms of preferred examples, it will be apparent to those persons of ordinary skill in the art that variations may be applied to the aspects described herein without departing from the concept, spirit, and scope of the disclosure and claims. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the disclosure as defined by the appended claims.

[0041] As known to persons having ordinary skill in the art, the word “grain” may be used to refer to crystallites of varying, randomly distributed, small sizes that together make up a piece of solid metal. Grain boundaries define surface areas where various grains contact each other. Grain boundaries are generally a weakness in the material (i.e., aweakness in the piece of solid metal). The grain boundaries, where two grains meet, have a disordered structure that reduces the strength of the metal in comparison to a sample of the solid metal where the grains have an ordered structure (i.e., a single crystal). Accordingly, removing grain boundaries could be advantageous, at least in terms of producing metals of superior strength (superior in comparison to samples that have pluralities of grain boundaries).

[0042] There are methods of casting metal products that allow the cast metal to grow as one single grain. Such methods may be generally referred to as investment castings or lost wax castings. In an investment casting process, accurate castings may be formed within a mold formed around a wax (or similar material) copy of the ultimately desired finished metal product. The wax is removed by melting and is replaced with molten metal poured into the mold. Investment castings, with single grain metal finished products, may be used for high performance metal applications, such as the first stage of turbine blades of a jet engine, where the first stage blades are positioned behind a combustor that is expelling very hot gas (that may be above the melting point of the metal used to fabricate the turbine blades) and are spinning around a shaft of the jet engine at high speed with large loads. However, because the chemistry of the investment cast metal has been optimized and because the investment cast products have no grain boundaries, the metal parts are able to withstand the high temperatures and high loads.

[0043] At least one challenge with investment casting is that engineers are limited in the shapes that can be made. For example, very complex shapes may be designed that may be good for aerodynamic, cooling, and performance aspects. Yet, those shapes may be impractical or impossible to fabricate using an investment casting process (e.g., because the internal copy of the desired part within an investment cast mold, when melted, loses important details of the desired part). Furthermore, fabricating intricate internal passages with a significant height-to-width ratio poses a difficulty for an investment casting process. Additionally, the creation of investment cast molds is a timeconsuming process. Although more than one finished product may be cast in a given investment cast mold, once the investment cast mold is filled with molten metal to create the one or more than one finished product, the investment cast mold will need to be destroyed to extricate the one or more than one finished product from the mold. Accordingly, there may be a great benefit to producing a metal part using an additive manufacturing process (distinct from the investment casting process), where theadditively manufactured metal part is a single crystal metal with one grain throughout the metal part.

[0044] Furthermore, an additive manufacturing process lends itself to the formation of complex shapes, the inclusion of cooling channels, speed and ease of modeling and prototyping, speed and ease of modification of the shape for prototyping, and repeatability with accuracies dependent on the 3D printer that formed a finished metal part, rather than on accuracies dependent on each iteration / copy of an investment cast mold. Moreover, few companies worldwide can make high-quality, high-precision, single crystal metal parts using investment casting. The small number of companies, coupled with a high demand for high quality, high precision, single crystal metal parts, results in lead times that could exceed one or more years.

[0045] In metal additive manufacturing, a desired (e.g., finished, final, completed) metal part is mathematically represented by thousands of horizontal cross-section “slices” stacked one atop another. A three-dimensional (3D) printer may be configured to direct either a laser beam or an electron beam at a leveled bed of unmelted metal powder and, using the energy realized at the focal point of the laser beam or electron beam, melt a shape corresponding to a cross-sectional layer of the desired metal part into a topmost layer of the unmelted metal powder. After melting the shape into the layer, the next layer of unmelted metal powder is added atop the just-processed layer. A respective shape corresponding to the cross-sectional slice of the next layer of the metal part is melted into the next layer. The process of adding the next layers of unmelted metal powder, causing the laser beam or electron beam to melt the next shapes corresponding to respective slices of the metal product into the next layers, is repeated until the desired 3D metal part is produced.

[0046] Several categories of metal additive manufacturing processes exist today. One category may be referred to as powder bed fusion or powder bed melting. In this category there are two subcategories. A first subcategory may be referred to as selective laser melting or laser powder bed fusion (L-PBF). In L-PBF, a high-power laser beam selectively melts a metal powder into a shape corresponding to a cross-section of one of thousands of slices of a desired (e.g., finished, final, completed) metal part. The high- power laser beam selectively joins or welds the particles of the metal powder together. Once all layers have been printed, the metal part may be removed from the surroundingunmelted metal powder. Many parts made using the L-PBF process require heat treatment to strengthen the metal end-product.

[0047] A second subcategory may be referred to as electron beam melting (EBM). The electron beam melting process does not use a high-power laser. Instead, as the name implies, it uses a high-power electron beam to selectively melt the metal powder. Unlike a laser process, which may be carried out at room temperature and pressure and with normal air or within an envelope of an inert gas, an electron beam melting process must be carried out in a vacuum, in a vacuum chamber that may be maintained at extremely hot temperatures (e.g., 1 ,000 - 1 ,500 degrees Celsius).

[0048] Fabrication of single crystal superalloys using powder bed fusion additive manufacturing technologies has been found to produce (e.g., form) an undesirable polycrystalline shell encapsulating a single crystal core. Unmelted metal powder in a powder bed surrounding a part during a powder bed fusion process or unmolten metal powder that may be trapped at an edge (e.g., a line or border at which a surface terminates, an external boundary, an external periphery, a zone including and immediately adjacent to the line, border, boundary, or periphery) of a molten zone may initiate the growth of the polycrystalline shell. Described herein are examples of a conversion of the polycrystalline shell into a single crystal by surface re-melting using various approaches. Various aspects described herein may be implemented during (e.g., in situ) or following (e.g., post-processing), a powder bed fusion additive manufacturing process. Various examples of heat sources, such as, but not limited to, laser beam, electron beam, induction, flame, or plasma, may be used in the exemplified processes of controlled surface re-melting.

[0049] Single crystal (SX) nickel-based superalloys may be used to produce blades for gas turbines in engines and power plants where excellent corrosion and oxidation resistance, superior mechanical properties, and exceptional high-temperature performance are required.

[0050] The processes of additive manufacturing and investment casting are different. Additive manufacturing processes may reduce a number of manufacturing steps and may reduce processing waste in comparison to investment casting processes. In addition, the additive manufacturing process, with its melting and re-melting of fine powder size in micron length and time scale, leads to high cooling rates of 103-106°C / s and a different metallurgical response to processing, in comparison to investment casting processing.

[0051] Solidification as it occurs in additive manufacturing processes gives rise to a very fine cellular or dendritic microstructure, with reduced dendritic segregation in comparison to conventional processing (e.g., investment casting processing). This aspect of solidification may remove or obviate a need for a lengthy chemical homogenization step. Due to the inherent high solidification velocities, combined with steep thermal gradients, the dendrite arm spacing is about two orders of magnitude smaller compared to a classical Bridgman process. As a result, the single crystals produced with additive manufacturing are homogenized within minutes. In addition, the solidification porosity scales with (e.g., is proportional to) the dendrite arm spacing. These additively manufactured single crystals show a level of homogeneity that cannot be reached with conventional methods (e.g., investment casting). The achieved level of homogeneity may lead to superior properties such as high temperature strength, oxidation resistance, creep strength, or fatigue life.

[0052] One of the challenges with powder bed fusion additive manufacturing of single crystal superalloys is the formation of a polycrystalline shell on the edge of the component (being manufactured) and in close proximity with the surrounding powder bed, where the powder may normally act as a nucleation site and may prevent a full single crystal component (e.g., a part) from being realized. The presence of the polycrystalline shell may limit the application of additive manufacturing produced superalloys due to a mismatch of mechanical properties and a lack of understanding of high-temperature complications.

[0053] Described herein are surface treatment processes that may convert a polycrystalline shell into single crystal by surface re-melting of the superalloy. The process may be conducted during an additive manufacturing process (e.g., in situ), or may be conducted following the additive manufacturing process, as a post-process event to the additive manufacturing process.

[0054] FIG. 1 is a conceptual block diagram with illustrations depicting two processes of surface re-melting of a polycrystalline shell 100 according to some aspects of the disclosure. A first process 102 during a powder bed fusion additive manufacturing process (e.g., in situ) utilizing a laser beam or an electron beam is represented as a first block. A second process 104 after (i.e., following) a powder bed fusion additive manufacturing process (e.g., post-processing) is represented as a second block. Both processes ultimately achieve the same result. As indicated, in association with both the first process102 and the second process 104, the powder bed fusion process may be a laser powder bed fusion process or an electron beam melting process, according to some aspects.

[0055] Regarding the first process 102 of in situ surface re-melting, a first graphic 106 represents a cross-section of a powder bed 108 filled with powder 110 (e.g., metal powder) enclosed by sidewalls 1 12 on the sides and a platen 1 14 (e.g., generally a flat plate) on the bottom. The platen 1 14 may be raised or lowered using a raising / lowering mechanism 1 16. The first graphic 106 also depicts a part 1 18 (e.g., a component) that is being produced by the additive manufacturing process (e.g., using either laser powder bed fusion or electron beam melting). A base of the part 118 is formed contiguously with the platen 1 14. At the top of the part 1 18, there exists an outer layer of PX 122. The majority of the part 118 is SX 124. In the example of the first graphic 106, the part 118 is represented with a rectangular cross section formed of, for example, hundreds or thousands of layers. According to the process, a depositor / spreader 120, which is overly simplified in its depiction as a solid black circle, traverses from one side of the powder bed 108 to the other as it deposits a new layer of powder 110 atop the topmost layer of powder 1 10 and smooths the new layer. Once deposited, the laser beam or electron beam (not shown) melts a cross section of the part being printed in the new layer of powder 1 10. Each new layer is added and melted. Once the new layer is melted, the raising / lowering mechanism 1 16 lowers the platen 1 14 by a predetermined distance, which lowers the part 1 18 and the powder 1 10 in the powder bed 108 by the predetermined distance. Thus, as the part 1 18 is built up, it is simultaneously being lowered along with the surrounding powder 1 10.

[0056] The second graphic 126 depicts the same components as the first graphic 106. To avoid cluttering the drawing, the reference numbers corresponding to the sidewalls 1 12, the platen 1 14, the raising / lowering mechanism 116, the part 118, the PX 122 and the SX 124 of the part 1 18 are not repeated. The second graphic 126 depicts an aspect that follows the first process 102. Namely, the aspect relates to a removal, for example, by vacuuming, or a displacement of unmelted metal powder surrounding the part 1 18 is represented as block 128. During block 128, a vacuuming tool 130 or a displacement tool 132 may be used to remove powder 110 adjacent to the PX 122.

[0057] The third graphic 134 depicts the same components as the first graphic 106 and the second graphic 126. To avoid cluttering the drawing, the reference numbers corresponding to the sidewalls 1 12, the platen 1 14, the raising / lowering mechanism 116,the part 1 18, the PX 122 and the SX 124 of the part 1 18 are not repeated. The third graphic 134 depicts an aspect that follows block 128. Namely, at block 140, once the powder 1 10 adjacent to the PX 122 is removed (thereby depriving the part 118 of nucleation sites from which PX 122 might grow), the existing PX 122 surrounding the part 1 18 may be remelted with a laser beam or electron beam 136 emitted from a laser or electron beam source 138 to transform the existing PX 122 into SX 124.

[0058] Turning now to the second process 104, which may occur instead of the first process 102, after the part 1 18 is formed in a powder bed fusion additive manufacturing process and is removed from the powder bed (e.g., from the powder bed 108). Accordingly, the second process 104 may be referred to as a post-processing process.

[0059] The second process 104 employs a heat source, such as a laser beam 142, an electron beam 144, an induction coil 146, a flame 148, or a plasma 150. The preceding list is exemplary and non-limiting. The heat source is used to remelt the PX 122 encapsulation and convert it into SX 124.

[0060] In the example of the fourth graphic 152, an induction coil 146 that is stationary while the part 1 18 is moved in the positive Y axis direction through the center of the induction coil 146. As depicted, the portions of the part 1 18 that have already been remelted and the portion of the part 118 that is undergoing remelting within the induction coil 146 has had the PX 122 encapsulation converted to SX 124.

[0061] In the example of the fifth graphic 154, a source 156 of a laser beam 142, an electron beam 144, a flame 148, or a plasma 150 is maintained in a stationary position while the part 118 is moved in the positive Y axis direction past the source 156. As depicted, the portions of the part 1 18 that have already been remelted and the portion of the part 118 that is undergoing remelting has had the PX 122 encapsulation converted to SX 124.

[0062] In conjunction with the first process 102 and the second process 104, the process parameters may be set in a way to produce the part 1 18 with a single crystal (SX 124) core encapsulated with a polycrystalline (PX 122) shell. As used herein, encapsulated may refer to enclosing a circumference (e.g., surrounding the Y axis) or an outer edge of the part 1 18, as opposed to completely enveloping the part 1 18 (e.g., on all sides, on all visible surfaces, including the top and bottom of the part 1 18). The following list provides an example of process parameters that may be utilized in connection with anelectron beam melting process during the fabrication of a part made of, for example, a nickel-based superalloy, such as but not limited to Alloy 5, (hereinafter “SX superalloy”).Beam speed: 300-750 mm / sBeam current: 5-12 mA Line offset: 0.1 -0.2 mm Focus offset: 0-30 mA Layer thickness: 50-70 urn

[0063] FIG. 2 is a schematic of a suction device 202 (a negative pressure device) including a gas jet device 204 (a positive pressure device) coaxial to (and within) the suction device 202 according to some aspects of the disclosure. The suction device 202 and the gas jet device 204 may be referred to collectively as an air powered removal device 200. FIG. 2 depicts a vacuuming in (e.g., sucking) of unmelted metal powder 206 into the suction device 202, where at least some of the unmelted metal powder 206 was blown by the gas jet device 204 according to some aspects of the disclosure. In the example of FIG. 2, the unmelted metal powder 206 is being removed from an area adjacent to an edge of a part 208 being additively manufactured.

[0064] During a printing of the part 201 , at the conclusion of the printing of at least one of: every layer or every predetermined plurality of layers, the air powered removal device 200 may remove unmelted metal powder from the edge of the part 201 . The gas being blown toward the unmelted metal powder 206 from the gas jet device 204 may displace the unmelted metal powder 206 away from the edge of the part 201 , while the suction device 202 vacuums at least some of the displaced unmelted metal powder 206 away from the region adjacent to the edge of the part 201 . The removal of the unmelted metal powder may be to a predetermined depth.

[0065] FIG. 3A illustrates a schematic of a first displacement member 302 that moves unmelted metal powder 300 away from the edges of a first part 304 during an additive manufacturing process according to some aspects of the disclosure. FIG. 3B illustrates a schematic of a second displacement member 306 that moves unmelted metal powder 300 away from the edges of a second part 308 during an additive manufacturing process according to some aspects of the disclosure.

[0066] Similar to the example of FIG. 2, in the examples of FIGs. 3A and 3B, during a printing process of a part (e.g., the first part 304 or the second part 308), at the conclusion of the printing of at least one of: every layer or every predetermined plurality of layers, afirst displacement member 302 or a second displacement member 306 may displace (e.g., move, dislodge, shift, dislocate) the unmelted metal powder 300 around the edges of the first part 304 or the second part 308 to a predetermined depth. In some examples, the first displacement member 302 may be a round bar (e.g., a rod, a cylinder) that moves along the edges of the first part 304. In some examples, the second displacement member 306 may be a spindle (e.g., a slender rounded rod that spins) or a rotating spiral shaft that extracts the unmelted metal powder 300 from the edge of the second part 308 to the desired depth. In some examples, the diameter of the first displacement member 302 or the second displacement member 306 may be on the order of 1 to 5 mm. The preceding range is for illustrative and non-limiting purposes, other diameters are within the scope of this disclosure.

[0067] Subsequent to the displacement of the unmelted metal powder 206 (FIG. 2) or unmelted metal powder 300 (FIGs. 3A, 3B) a laser beam or an electron beam may rescan the edge of the part 201 , 304, 308 with sufficient energy to re-melt the edge of the part 201 , 304, 308. Because of the displacement, the re-melting is performed in the absence of adjacent unmelted metal powder (i.e., because the adjacent unmelted metal powder was displaced). The re-melted metal powder may penetrate several layers in the vertical direction and inward to the SX core of the part 201 , 304, 308 and therefore melt / re- melt the edge of the part 201 , 304, 308. This re-melting either, or both of, re-melts any polycrystalline metal formed adjacent to the edge of the part that was not removed or displaced, and / or re-melts the edge of the single crystal core (also referred to herein as a single crystal metal core) and thereby extends the single crystal to the edge of the part 201 , 304, 308 without formation of any polycrystalline shell. In other words, any polycrystalline shell remaining at the edge may re-melt and when it solidifies it will follow the same crystal orientation of the single crystal core.

[0068] The printing process may repeat for the next layer or the next predetermined number of layers and then the displacement and re-melting aspects may be repeated.

[0069] In connection with a post-process aspect, the part may be fully fabricated (e.g., without in situ re-melting) and may therefore include a single crystal core with a polycrystalline shell. In some examples, the polycrystalline shell may be 1 to 2mm in thickness.

[0070] The polycrystalline shell may be exposed to localized heating that scans over the surface of the part and re-melts the polycrystalline shell to a predetermined depth (e.g., a melt pool depth), where the predetermined depth reaches the single crystal core.

[0071] The re-melted polycrystalline shell solidifies to a single crystal that follows the crystal orientation of the single crystal core. The heat input may be adjusted to slowly fade the energy input during solidification (e.g., during cooling), to avoid early solidification of a surface layer.

[0072] Multiple repetitions of localized melting and solidification may be utilized to develop the single crystal layer to the surface of the part.

[0073] Several examples of heating techniques and process conditions that may be employed, and several examples of options for re-melting the surface of a part, are described below.

[0074] In one example, a laser may be used for reheating. Various types of lasers with different powers may be applied to this process. The laser power may be sufficient to create enough depth in the melt pool such that the melt pool can reach the single crystal core (i.e., the surface of the single crystal core). If the process is done under a controlled atmosphere utilizing a protective gas, the flow of the protective gas may be minimized to avoid early solidification of the outer surface of the re-melted portion of the part.

[0075] In one example, an electron beam may be used for reheating. Following the same process as with lasers, an electron beam may be used to process the parts in a vacuum.

[0076] In one example a flame (e.g., a high-temperature flame) may be used for reheating. In the example, a torch emitting the flame may be coupled to a precision positioning system. However, there may be less control over the location and size of the melt pool when using a flame in comparison to melt pools produced using a laser beam or an electron beam. Additionally, the spot size of a flame emitted from a torch may be large relative to the size of a laser beam or electron beam.

[0077] In one example, a plasma may be used for reheating. For example, a plasma arc technique may be applied to reheat a large surface area of the part; however, control over the melt pool size and depth may be limited when using a plasma arc technique.

[0078] In one example an induction heating process may be used for reheating. In the example, the induction heating process may melt a large area on an edge of the part. Utilizing induction heating with a selected alternating current (AC) frequency or range ofAC frequencies, the depth of the induction heating formed melt pool may be adjusted. Furthermore, induction heating may provide for a frequency sweep that may be used to manipulate the depth of the melt pool and may be used to controllably (and carefully) solidify the molten zone in a direction beginning at the single crystal surface layer or the single crystal core to an outer surface of the part.

[0079] In general, with regard to heat input, the power or energy input may be gradually decreased by adjusting process parameters. This adjustment permits an initiation of solidification from the SX region that may be caused to progress towards the surface gradually. For example, in connection with an induction heater, a frequency sweep may be used to regulate the depth of melting and progressively reduce the thickness of the melted zone. For example, in connection with a laser or an electron beam, the power may be decreased, or multiple re-melting occasions may be utilized.

[0080] FIG. 4 is a schematic of a partial re-melting of a surface of a sample 500 using a 2kW laser according to some aspects of the disclosure. In FIG. 4, a build direction 402 (<100> SX crystallographic direction shown by build direction 402 block arrow) of the sample 500 is in the Z axis direction as depicted in the figure. A 15 mm x 15 mm surface region 404 of the polycrystalline shell with <1 10> crystal orientation was remelted with a 2 kW disk laser 406 with an average energy input (an area energy density) of 400-600 J / mm2(as depicted in FIG. 4). To demonstrate the concept of re-melting, the sample 500 is a single crystal sample that was manufactured using an electron beam melting process (resulting in a part with a single crystal core and a polycrystalline shell) and was surface heat treated using a 2 kW disk laser. A photomicrograph of the sample 500 before heat treatment is provided in FIG. 5. A photomicrograph of the sample 500 after heat treatment is provided in FIG. 6.

[0081] The <1 10> crystal orientation plane is a crystal plane that is perpendicular to the <1 10> direction, which is a line at a 45-degree angle to the X and Y axes of the crystal lattice. Miller indices 408 are included in FIG. 4 for reference purposes. The flow of the shielding gas used in connection with the laser was minimized to avoid early solidification of the surface of the part.

[0082] FIG. 5 and FIG. 6 show the microstructure of the sample 500 before and after treatment, respectively. In FIG. 6, the electron backscatter diffraction (EBSD) inverse pole figure (IPF) maps 610 show that the polycrystalline shell 504 (FIG. 5) (e.g., apolycrystalline layer) was fully converted to single crystal 602 in a re-melted zone 608 following solidification after surface re-melting.

[0083] FIG. 5 is a photomicrograph of a sample 500 of a part fabricated using an electron beam melting additive manufacturing process using a nickel-based superalloy, such as but not limited to Alloy 5 (hereinafter “SX superalloy”) according to some aspects of the disclosure. The sample 500 exhibits a single crystal core 502 and a polycrystalline shell 504 according to some aspects of the disclosure. As used herein, the terms single crystal (used perhaps in engineering parlance) and single grain (used perhaps in metallurgical parlance) are synonymous. The part (from which the sample 500 was collected) was produced using an additive manufacturing process during which a plurality of SX superalloy unmelted metal powder layers had melted into a corresponding plurality of cross-sections (e.g., shapes) of a corresponding plurality of layers (e.g., slices) of a desired metal product. During the additive manufacturing process, each cross-sectional shape of the desired metal product was melted, one atop the next, using an electron beam melting process. After each slice was melted (e.g., printed), a new layer of unmelted metal powder was added atop a just solidified layer and then the new respective cross-sectional slice was melted into the new layer of unmelted metal powder and into at least a portion of the previously solidified layer. The finished metal product is formed of a continuous intermixed plurality of solidified cross-sectional slices.

[0084] However, the continuous intermixed plurality of solidified cross-sectional slices does include discontinuities manifested as a polycrystalline shell 504. It is noted that the entire central region 508 of the sample 500 is a single crystal despite the appearance of some random discolorations (i.e., whitish drops, splotches, and linear streaks visible in the sample 500). The random discolorations in the central region 508 of the sample 500 are attributed to the handling of the sample 500.

[0085] The polycrystalline shell 504 appears in a zone between the solidified single crystal core 502 SX superalloy (in the central region 508) and a region of unmelted metal powder (not shown) outboard of the polycrystalline shell 504. The sample 500 was obtained using cross-section microscopy. According to cross-sectional microscopy processes, the sample 500 may be embedded in an epoxy 506, cross-sectioned and polished in a Y-X plane (parallel to the plane of the paper). The sample 500 was then etched using an etching solution. The etching permits visualization of various grains in the sample 500.

[0086] The sample 500 includes a plurality of horizontal layers in the X-Z plane (not distinguishable in the photomicrograph). Each layer is formed atop a preceding layer using the described additive manufacturing process that forms the layers in the positive Y-axis direction from the bottom of the sample 500 (e.g., at the origin of the Y-axis) toward the top of the sample 500.

[0087] The edge grains of the polycrystalline shell 504 may form by nucleation from metal powder attached to a surface of the desired finished metal part (i.e., attached to an outer boundary of metal powder intentionally melted using the electron beam). According to aspects described herein, removal of the unmelted metal powder from the edges of a given layer (or layers) of the part prevents nucleation of the edge grains during re-melting of the remaining edge, the re-melting and subsequent re-solidification converting any remaining polycrystalline metal at the remaining edge into single crystal metal.

[0088] As indicated by the scale included with FIG. 5, the thickness of the polycrystalline shell 504 is about 1 mm (1000 pm). Certain parts, such as, but not limited to high performance turbine blades, may have a desired exterior wall thickness of 1 mm. Given that the thickness of a desired single crystal exterior wall and an undesired polycrystalline shell undesirably coupled to that exterior wall are on the same order, chemical etching may not be a feasible way to remove the polycrystalline shell. For example, due to different localized concentrations of the chemical etch solution, bubble formation (as a byproduct of an etching process), surface contaminants, and surface features of a given part, in any given unit of time, a chemical etch may remove 1 mm of material from one area and, immediately adjacent to the one area, remove 2 mm of material. Such a difference in the depth of material removed by a chemical etching process could conceivably remove both the desired single crystal exterior wall and the undesired polycrystalline shell.

[0089] According to some aspects, the thickness of the polycrystalline shell 504 is independent of the thickness of the single crystal metal beneath the polycrystalline shell 504. Using FIG. 5 as an example, without limitation, the thickness in the X-axis dimension of the single crystal core 502 (i.e., the metal in the central region 508) is about 10 mm. In comparison, the thickness in the X-axis dimension of each of the left and right portions of the polycrystalline shell 504 is about 1 mm. It has been observed that the thickness of the polycrystalline shell 504 remains at about 1 mm regardless of whether the thickness ofthe single crystal core 502 in the central region 508 is increased (e.g., to 100 mm) or decreased (e.g., to 3 mm).

[0090] In practice, without at least partial elimination of nucleation material (e.g., unmelted metal powder adjacent to solidified metal powder) from the desired external wall surface, the growth of the polycrystalline shell 504 makes it difficult, if not impossible, to manufacture single crystal metal walls that have a thickness of about 1 mm.

[0091] FIG. 6 is a photomicrograph of the sample 500 of FIG. 5 (manufactured using an electron beam melting additive manufacturing process) after being surface heat treated and having any polycrystalline shell 504 converted, in the re-melted zone 608, to a single crystal 602 according to some aspects of the disclosure. The polycrystalline shell 504 was fully converted to single crystal 602 in the re-melted zone 608, as evidenced by the electron backscatter diffraction (EBSD) inverse pole figure (IPF) maps 610 and the inset photomicrographs 612. The inset photomicrographs 612 show a portion of an edge of the sample 500 before re-melting (e.g., upper image identifying polycrystalline shell 504) and after re-melting (e.g., lower image identifying the converted 614 polycrystalline (PX) shell to single crystal (SX)). As known to those of ordinary skill in the art, an IPF map combines a locally detected orientation with a crystallographic description of a single reference direction. The inset photomicrograph 612 shows that the polycrystalline shell

[0092] FIG. 7 is an image with an inset illustration of a pair of 3D printed metal products 700 formed using an electron beam melting process according to some aspects of the disclosure. The 3D printed metal products 700 exhibit a polycrystalline shell 704 such as the polycrystalline shell 504 as shown and described in connection with FIG. 5. The edge grains (i.e., the polycrystalline shell 704) may be formed by nucleation on metal powder attached to the outer surface 702 of each respective 3D printed metal products 700. The polycrystalline shell 704 formed on the outer surface 702 of each of the pair of 3D printed metal products 700 may impinge into the final (net) surface of each of the pair of 3D printed metal products 700. An accumulation of unmelted metal powder 706 is depicted between the pair of 3D printed metal products 700. The thickness of the polycrystalline shell 704 in the example of FIG. 7 is about 1 mm, as shown.

[0093] In solidification, when a metal is molten, and it solidifies, the solidification begins on a surface that is cooler than the molten metal. A first atom of the molten metal may land on the cooler surface, cool down, solidify, and remain in place on the cooler surface. This atom and / or the surface to which it is attached may be referred to as a nucleationpoint. Other atoms may attach to the nucleation point, cool down, solidify, and remain in place, thus building the solid portion of the metal from the original cooler surface into the remaining molten metal. In greater detail, as known to persons of ordinary skill in the art, nucleation may be understood as an initial process that takes place in the formation of a crystal from a solution, a liquid, or a vapor, in which a small number of ions, atoms, or molecules become arranged in a pattern characteristic of a crystalline solid, forming a site upon which additional ions, atoms, or molecules are deposited as the crystal grows.

[0094] FIG. 8 is a simplified, not-to-scale, artist’s rendition of a plurality of the uppermost layers (where the plurality of layers are not individually distinguished to avoid cluttering the drawing) of a cross-section of a second sample 800 of a metal product undergoing fabrication utilizing an electron beam melting, metal additive manufacturing process according to some aspects of the disclosure. The second sample 800 may be similar to the sample 500 as shown and described in connection with FIGs. 5 and 6. The second sample 800 includes a single crystal 802, a polycrystalline shell 804, a bed of unmelted metal powder 806 in which the finished metal product is fabricated, and an intermixed region 808 (e.g., a melt-pool) of melted metal powder and re-melted single crystal 802 that is depicted atop uppermost layer(s) of the single crystal 802. It is noted that the width of the melt-pool is exaggerated; in practice, the melt-pool may be localized around the focal point of the electron beam, on the surface of the metal product.

[0095] During the process of additive manufacturing, a layer of unmelted metal powder 806 is spread atop a previously solidified layer of the metal part being fabricated. A portion of the unmelted metal powder 806 (corresponding to a cross-section of a slice of a desired metal part being fabricated) is completely melted along with a portion of the uppermost layer(s) of the single crystal 802. The melting of the unmelted metal powder 806 and the portion of the uppermost layer(s) of the single crystal 802 occurs simultaneously, so that both the melted metal powder and the re-melted single crystal form the intermixed region 808 of melted metal powder and re-melted single crystal metal.

[0096] The entire thickness (in the Y-axis direction) and width (in the X-Z plane) are allowed to solidify, thus building one layer atop a next layer, in the Y-axis direction. It will be understood that each time an unmelted metal powder 806 layer is added, and that unmelted metal powder 806 layer (corresponding to a cross-sectional slice of the finished metal product) is melted and intermixed with a re-melted portion of the single crystal 802, the atoms in the intermixed region 808 solidify beginning on atoms (e.g., surface atoms)of what is already the solid single crystal 802. Because the atoms of the single crystal 802 are already aligned with each other, the atoms of the melted metal powder and re-melted single crystal in the intermixed region 808 will align with the already aligned atoms of the single crystal 802 during the solidification process. The newly solidified atoms will have the same alignment as those of the already aligned atoms of the single crystal 802. In other words, in response to an intermixed region 808 of atoms that include newly melted metal powder and re-melted single crystal 802, given that nucleation of the atoms in the intermixed region 808 begins on the surface of the already aligned atoms of the solidified single crystal 802, the newly solidified atoms will, by their own nature, align with and maintain the alignment of the atoms already present in the solidified single crystal 802.

[0097] However, because the part being fabricated is built on a powder bed table that is covered with unmelted metal powder 806 each time a new layer is added, atoms of melted metal in the intermixed region 808 adjacent to 810 the particles, or grains, of unmelted metal powder 806 (at the left and right edges of the second sample 800) nucleate upon those particles, or grains, and grains of metal begin to grow toward an already existing surface 812 of the single crystal 802, creating the polycrystalline shell 804. Meanwhile, atoms adjacent to the already existing surface of the single crystal 802 nucleate on that existing surface and begin to grow from that existing surface.

[0098] Accordingly, examples of the fabrication of metal parts formed as a single crystal 802 metal using additive manufacturing with a 3D metal printer are described herein. The additive manufacturing process may be an electron beam melting process, a high-power laser process (e.g., L-PBF), or a similar process that melts metal powder or metal bearing material at the edges (e.g., walls) of the metal part. In the examples, the polycrystalline shell 804 may be prevented, converted to single crystal, or removed.

[0099] According to a first aspect, metal powder, which would remain as unmelted metal powder 806 adjacent to an edge of the metal part following the printing of a given layer of the metal part, may be removed before spreading a new layer of unmelted metal powder 806 and before the printing (e.g., the melting) of the shape in the new layer of unmelted metal powder 806 corresponding to a cross-section of a slice of the metal product. After removal, the edge of the metal part may be re-melted. The removal of the unmelted metal powder 806 (from areas adjacent to the edges of the part) eliminates a possibility of the atoms of molten metal (in what will become an intermixed region 808 of melted metal powder and re-melted single crystal 802) from using particles of theunmelted metal powder 806 as nucleation sites, thus preventing, before it is created, the formation of the polycrystalline shell 804.

[0100] In an electron beam melting process, unmelted metal powder is spread in a layer and then the layer of unmelted metal powder may be sintered. For example, the electron beam may be configured to scan the layer at a power level that is not sufficient to melt the metal powder but is sufficient to cause the particles of the metal powder to stick together. In other words, a process of sintering may cause the unmelted metal powder to coalesce into a solid or porous mass by heating without liquefaction. Sintering may be used In the electron beam melting process because electrons from the electron beam gun are emitted into the vacuum chamber holding the printing apparatus and metal powder. Particles of the unmelted metal powder may become negatively charged by the electrons. Sintering, which coalesces adjacent particles, may be utilized to prevent adjacent negatively charged particles from being repelled electrostatically from one another. In some examples, where positive charges are pumped into the vacuum chamber to counteract and neutralize the negative charges emitted by the electron gun, sintering may be avoided.

[0101] In an electron beam melting process where sintering is used, the unmelted (but coalesced) metal powder particles may be attached to the part being printed and are therefore present and available to act as (undesired) nucleation sites.

[0102] In contrast, in a laser powder bed fusion process, the metal powder is spread in a layer but not sintered. That is, the metal powder does not coalesce prior to printing (e.g., melting). However, in the laser powder bed fusion process, loose unmelted metal powder particles adjacent to a melt-pool, which would remain as unmelted metal powder 806 subsequent to a printing of a given layer, do not remain at their locations but are drawn into (or blown into) the melt-pool. The melt-pool therefore includes intended melted metal powder, re-melted single crystal metal, and unintended loose unmelted metal powder particles adjacent to the melt-pool (that were drawn into or blown into the melt-pool). Because the loose unmelted metal powder particles adjacent to the melt-pool are drawn into (or blown into) the melt-pool, those particles are not available as nucleation sites to the atoms of molten metal in the melt-pool (e.g., in the intermixed region 808).

[0103] In some examples, an inert gas may envelope a melt-pool and displace oxygen, nitrogen, and atmospheric contaminants that may cause inconstancies in the finished product. According to some examples, the inert gas may be called a shielding gas. Insome laser powder bed fusion machines, the inert gas may be close to atmospheric pressure (e.g., very slightly above atmospheric pressure). Some laser powder bed fusion machines include a gas flow pump that flows the inert gas over the surface of the powder bed at a flow rate of about 1 - 3 meters per second (m / s). This flow rate may be fast enough to remove soot that is generated by the melting process, but not fast enough to blow (e.g., move) loose particles of metal powder in any direction. Other flow rates are within the scope of the disclosure.

[0104] FIG. 9 is a block diagram of an example of system 901 that may be used to displace unmelted metal powder from edges of one or more additively manufactured printed layers of a 3D printed metal part (hereinafter “the part” 902) during fabrication (e.g., in situ) according to some aspects of the disclosure. The system 901 includes an apparatus 900 that may be utilized with an electron beam melting process or a laser powder bed fusion process. The apparatus 900 may include a recoater head 904, a tool actuator 906 slidingly coupled to the recoater head 904, and a tool 908 fixedly, or optionally rotatably, coupled to the tool actuator 906.

[0105] In the example of FIG. 9, the apparatus 900 is located in a vacuum chamber 914 in an electron beam melting 3D printer 916 and is thus configured for an electron beam melting process. The same apparatus 900 may be used in a laser powder bed fusion process, in which case the vacuum chamber 914 and the electron beam melting 3D printer 916 would be removed from FIG. 9 and a laser (not shown) would be substituted for the electron beam gun 918. Otherwise, the apparatus 900 (including the recoater head 904, the tool actuator 906, and the tool 908) as well as the gantry driver 912, the worm drive 910, the powder bed 920, the part 902, and the gantry (not shown) may be used in either an electron beam melting process or a laser powder bed fusion process.

[0106] The recoater head 904 may include one or more servo(s), motor(s), linear stepper motor(s), or the like (not shown) to effectuate vertical (up-down) motion (i.e., translation along the Z-axis). The tool actuator 906 may include one or more servo(s), motor(s), linear stepper motor(s), or the like, or a combination thereof (not shown) to effectuate vertical (up-down) motion (i.e., translation along the Z-axis) and to optionally effectuate rotational motion of the tool 908 (i.e., rotation about the Z-axis).

[0107] In some examples, the tool may be at least one of: a suction device, a combined suction and gas jet device, or a displacement member (such as, but not limited to, a rodor a cylinder, which may or may not rotate), a rotating spindle, rotating auger, a rotating spiral shaft, or the like.

[0108] In some examples, where the tool 908 is configured to remove or displace unmelted metal powder (e.g., sintered or un-sintered metal powder that lies adjacent to an outer edge of a border of the part 902), the tool may be, for example, a brush, a comb, a plurality of whiskers, a paddle or beam of any cross-section or combinations of crosssections (e.g., circular, rectangular, oval, D-shaped, etc.) or the like. In other examples, the tool 908 may be, for example, a rod, a cylinder (which may or may not rotate), a rotating spindle, rotating auger, a rotating spiral shaft, or the like. As illustrated, the tool actuator 906 may optionally be configured to rotate the tool 908. The tool actuator 906 may be configured to rotate the tool 908 at a given speed or a variable speed and in either direction; FIG. 9 only illustrates the clockwise direction to avoid cluttering the drawing. In some examples, where the tool 908 is configured to remove unmelted metal powder (e.g., sintered or un-sintered metal powder that lies adjacent to an outer edge of a border of the part 902) by vacuum action, the tool 908 may be, for example, a suction device, a gas jet device, or a combination of the suction device and the gas jet device (previously referred to as an air powered removal device). In examples, the tool 908 may be a combination of any of the tools listed above (e.g., a combination of an air-powered device and a displacement member), and may be used together (e.g., at the same time, though displaced in space) or sequentially (e.g., one after another). The preceding lists are exemplary and non-limiting. Although not shown to avoid cluttering the drawing, the tool 908 may be any combination of the preceding types of tools and the tool actuator 906 may be configured to carry more than one tool 908 or any combination of more than one tool. For example, the tool 908 may be a spaced apart, adjacent, or coaxial combination of a cutting tool, a displacement member, and a suction device or air-powered device. The preceding combinations are illustrative and non-limiting. Any combination of two or more types of tools is within the scope of the disclosure.

[0109] According to some aspects, the recoater head 904 may be coupled to a worm drive 910. The worm drive 910 may be rotatably coupled to a gantry driver 912. The gantry driver may include one or more servo(s), motor(s), linear stepper motor(s), or the like (not shown). The gantry driver 912 may be configured to rotate the worm drive 910 clockwise and counterclockwise (at separate times) about a longitudinal axis of the worm drive 910 (e.g., about a Y-axis) to effectuate the left-right motion of the recoater head 904 (i.e.,translation along the Y-axis). The gantry driver 912 may be coupled to a gantry (not shown) and may be configured to effectuate forward-backward motion of the recoater head 904 (i.e., translation along the X-axis (where the X-axis is perpendicular to the plane of the figure)) by moving the gantry in the forward-backward directions. Worm gears and / or tracks that enable the forward-backward motion of the gantry, and the gantry itself, are omitted from FIG. 9 to avoid cluttering the drawing.

[0110] FIG. 9 depicts the apparatus 900 within a vacuum chamber 914 within an electron beam melting (EBM) 3D printer 916. An electron beam gun 918 is depicted above a powder bed 920. However, the apparatus 900 is not limited to placement within a vacuum chamber 914 and is not limited to placement within a vacuum chamber 914 of an EBM 3D printer 916. For example, the apparatus 900 may be utilized with a laser (which would replace the electron beam gun 918) outside of a vacuum chamber 914 in connection with a laser powder bed fusion (L-PBF) 3D printer (not shown).

[0111] FIG. 9 also depicts a controller 922 employing one or more processors (generally represented by processor 924) according to some aspects of the disclosure. Examples of processor 924 include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. In various examples, the processor 924 may be configured to perform any one or more of the functions described herein. That is, the one or more processors (generally represented by processor 924), as utilized in the controller 922, may be configured to, individually or collectively, implement any one or more of the methods, processes, or aspects described and illustrated, for example, in FIGs. 5, 9, 8, 4, 5, and / or 6.

[0112] In this example, the controller 922 may be implemented with a bus architecture, represented generally by the bus 926. The bus 926 may include any number of interconnecting buses and bridges depending on the specific application of the controller 922 and the overall design constraints. The bus 926 communicatively couples together various circuits, including one or more processors (represented generally by the processor 924) and one or more memories (represented generally by a memory I computer-readable medium 928). The bus 926 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, whichare well known to persons having ordinary skill in the art, and, therefore, will not be described any further.

[0113] A bus interface 930 provides an interface between the bus 926, the gantry driver 912, the recoater head 904, and the tool actuator 906. The bus interface 930 may provide an interface between the bus 926 and a user interface 932 (e.g., keypad, display, touch screen, speaker, microphone, control features, vibration circuit / device, etc.). Of course, such a user interface 932 is optional and may be omitted in some examples.

[0114] One or more processors, represented individually and collectively by processor 924, may be responsible for managing the bus 926 and general processing, including the execution of software stored in / on the memory I computer-readable medium 928. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. The software (e.g., instructions), when executed by the processor 924, causes the controller 922 via the gantry driver 912, the recoater head 904, the tool actuator 906, and the tool 908 to perform the various processes and functions described herein for any particular apparatus.

[0115] The memory I computer-readable medium 928 may be a non-transitory computer-readable medium and may be referred to as a computer-readable storage medium or a non-transitory computer-readable medium. The non-transitory computer- readable medium may store computer-executable code (e.g., processor-executable code). The computer executable code may include code for causing a computer (e.g., a processor) to implement one or more of the functions described herein. A non-transitory computer-readable medium includes, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., a compact disc (CD) or a digital versatile disc (DVD)), a smart card, a flash memory device (e.g., a card, a stick, or a key drive), a random access memory (RAM), a read only memory (ROM), a programmable ROM (PROM), an erasable PROM (EPROM), an electrically erasable PROM (EEPROM), a register, a removable disk, and any other suitable medium for storing software and / or instructions that may be accessed and read by a computer. The memory / computer-readable medium 928 may reside in the controller 922, external tothe controller 922, or distributed across multiple entities, including the controller 922. The memory I computer-readable medium 928 may be embodied in a computer program product or article of manufacture. By way of example, a computer program product or article of manufacture may include a computer-readable medium in packaging materials. Persons having ordinary skill in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system. The memory I computer-readable medium 928 may also be used to store data that is manipulated by the processor 924 when executing software (instructions 929).

[0116] According to one example, the controller 922 may be configured to perform an electron beam melting process (e.g., in the vacuum chamber 914 of the electron beam melting 3D printer 916), use the recoater head 904 to spread and level a layer of unmelted metal powder, optionally sinter the layer of unmelted metal powder, and melt a shape corresponding to a layer (e.g., a slice) of what will become the (finished) 3D printed part. At the end of each melting process or the end of a predetermined number of melting processes (or layers), before recoating the just-processed layer with a new layer of unmelted metal powder, the controller may be configured to use a displacement member (or suction or air-powered device) coupled directly to the recoater head 907 or coupled indirectly via the tool actuator 906 to displace (or remove) the unmelted metal powder (or sintered metal powder) from around the edge of the part to a predetermined depth. Subsequent to the displacement (or removal) of the unmelted metal powder (or sintered metal powder) from around the edge of the part, the controller may be configured to remelt the edge to a predetermined depth. With unmelted metal powder displaced (or removed) from the edge of the part, any polycrystalline shell that may have formed during the first melt is re-melted and takes on the orientation of a single crystal at the core of the part. Once complete, the controller may be configured to return to the process of recoating and leveling, optionally sintering, and melting a next shape corresponding to a next layer of the 3D printed part or a predetermined plurality of layers of the 3D printed part of what will become the (finished) 3D printed part. It is noted that more metal powder than usual may be needed to “refill” the areas around the edge of the part where unmelted metal powder was displaced or removed.

[0117] In greater detail, the controller 922 (or one or more processors configured to, individually or collectively, based at least in part on information stored in one or morememories) may be configured to spread, utilizing the recoater head 904, a layer of unmelted metal powder on the powder bed 920, melt, utilizing an electron beam emitted by the electron beam gun 918, a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part. The controller 922 may be further configured to repeat the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder. The controller 922 may be further configured to remove, utilizing the tool 908 coupled to the tool actuator 906 coupled to the recoater head 904 (or coupled to another movable platform controlled by the controller 922) metal powder adjacent to a first edge of the shape, re-melt, utilizing the electron beam gun 918, the first edge of the shape, and repeat the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers, or all, or substantially all, or some predetermined number, or some predetermined percentage of the layers of the additively manufactured 3D printed part are printed.

[0118] In some examples, the melting and re-melting may be performed by a laser in place of the electron beam gun 918. In some examples, the displacing, utilizing the tool, of the metal powder adjacent to the first edge of the shape may be a removal to a predetermined depth relative to a presently printed uppermost surface of the 3D printed part. In some examples, the tool is at least one of: a suction device, a combined suction and gas jet device, a displacement member such as a rod, or a cylinder, a rotating spindle, an auger, or a spiral shaft. The preceding list is exemplary and non-limiting.

[0119] In some examples, the controller 922 may be further configured to spread the layer of unmelted metal powder on the powder bed utilizing the recoater head 904 and position the tool 908 adjacent to the first edge of the shape utilizing the tool actuator 906 coupled to the recoater head 904.

[0120] In some examples, the additively manufactured 3D printed part (e.g., a first edge of the shape of the layer of the additively manufactured 3D printed part), prior to the remelting, includes: a first portion of single crystal metal, central to the shape and approaching the first edge from within the shape. The first portion of the single crystal metal having been nucleated upon a surface of a preexisting single crystal metal. The additively manufactured 3D printed part (e.g., a first edge of the shape of the layer of the additively manufactured 3D printed part), prior to the re-melting, also includes a second portion of polycrystalline metal, proximal to the shape and approaching the first edge fromoutside the shape. The second portion of polycrystalline metal having been nucleated upon the unmelted metal powder rather than on the surface of the preexisting single crystal metal. The first edge corresponds to a projection of a final outer wall of the 3D printed part on the layer of the unmelted metal powder. In some examples, the first edge (prior to re-melting) surrounds the additively manufactured 3D printed part, or the shape (at least on its sides), and includes at least one of: single crystal metal, or polycrystalline metal.

[0121] In other words, in some examples, the additively manufactured 3D printed part, prior to the re-melting, includes a preexisting single crystal metal core, a single crystal metal zone surrounding the preexisting single crystal metal core, the single crystal metal zone formed in an outward direction relative to the preexisting single crystal metal core and formed via nucleation upon the preexisting single crystal metal core, and a polycrystalline metal zone surrounding the single crystal metal zone, the polycrystalline metal zone formed in an inward direction toward the single crystal metal zone and formed via nucleation upon the unmelted metal powder, where the first edge corresponds to a projection of a final outer wall (e.g., a net dimension) of the additively manufactured 3D printed part on the layer of the unmelted metal powder. In this example, the first edge (prior to re-melting) surrounds the additively manufactured 3D printed part (at least on its sides) and includes at least one of: single crystal metal, or polycrystalline metal.

[0122] In some examples, re-melting the first edge forms a second edge that is devoid of polycrystalline metal. In other words, prior to re-melting, the edge (where the edge is referred to herein as the first edge prior to re-melting) included polycrystalline metal; after re-melting, the edge (where the edge is referred to herein as the second edge after remelting) is devoid of the polycrystalline metal. Accordingly, the same edge that prior to remelting included polycrystalline metal is devoid of polycrystalline metal after re-melting. The polycrystalline metal was converted to single crystal metal as a result of the remelting.

[0123] FIG. 10 is a flow chart illustrating an example process 1000 (e.g., a method) of metal 3D printing utilizing additive manufacturing and an electron beam melting process in accordance with some aspects of the disclosure. As described below, some or all illustrated features may be omitted in a particular implementation within the scope of the present disclosure, and some illustrated features may not be required for the implementation of all examples. In some examples, the process 1000 may be carried outby the apparatus comprising the system 901 , as shown and described in connection with FIG. 9. In some examples, the process 1000 may be carried out by any suitable apparatus or means for carrying out the functions or algorithm described below.

[0124] At block 1002, the apparatus may be configured to spread a layer of unmelted metal powder on a powder bed. In one aspect, the spreading the layer of unmelted metal powder on the powder bed may be performed utilizing a recoater head, and positioning the tool adjacent to the first edge of the shape may be performed utilizing a tool actuator coupled to the recoater head. For example, the recoater head 904 of the apparatus, as shown and described in connection with FIG. 9, may provide a means for spreading a layer of unmelted metal powder on a powder bed.

[0125] At block 1004, the apparatus may be configured to melt a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part. In one aspect, the melting and the re-melting may be performed with an electron beam. In another aspect, the melting and the re-melting may be performed with an electron beam. In one example, the shape, the additively manufactured 3D printed part, prior to the re-melting, includes: a first portion of single crystal metal, central to the shape and approaching, from within the shape, the first edge, the first portion having been nucleated upon a preexisting surface of the single crystal metal, and a second portion of the polycrystalline metal, proximal to the shape and approaching, from outside the shape, the first edge, the second portion having been nucleated upon the unmelted metal powder rather than on the preexisting surface of the single crystal metal, and the first edge corresponds to a projection of a final outer wall of the 3D printed part on the layer of the unmelted metal powder. According to some aspects, the first edge surrounds the additively manufactured 3D printed part and includes at least one of: single crystal metal, or polycrystalline metal. According to such aspects, re-melting the first edge forms a second edge that is devoid of polycrystalline metal. For example, the electron beam gun 918 of the apparatus, as shown and described in connection with FIG. 9, may provide a means for melting a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of the additively manufactured 3D printed part.

[0126] At block 1006, the apparatus may be configured to repeat the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder. For example, the controller 922 orthe processor 924 may provide a means for repeating the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder.

[0127] At block 1008, the apparatus may be configured to displace, utilizing a tool, the unmelted metal powder adjacent to a first edge of the shape. According to one aspect, the displacing, utilizing the tool, of the metal powder adjacent to the first edge of the shape may be performed to a predetermined depth relative to a presently printed uppermost surface of the 3D printed part. According to some aspects, the tool may be at least one of: a suction device, a combined suction and gas jet device, a displacement member such as a rod or a cylinder, a rotating spindle, an auger, or a spiral shaft. The preceding list is exemplary and non-limiting. For example, the tool 908 and the tool actuator 906 may provide a means for displacing, utilizing a tool, metal powder adjacent to a first edge of the shape.

[0128] At block 1010, the apparatus may be configured to re-melt the first edge of the shape. That is, the first edge was previously melted, for example at block 1004, and is now re-melted at block 1010. Re-melting the first edge forms a second edge that is devoid of polycrystalline metal. In other words, the re-melting has converted the polycrystalline metal in the edge into single crystal metal. In other words, the apparatus may be configured to re-melt polycrystalline metal in the edge and convert the polycrystalline metal into single crystal metal in the re-melted edge. For example, the electron beam gun 918 as shown and described in connection with FIG. 9, may provide a means for remelting the first edge of the shape.

[0129] At block 1012, the apparatus may be configured to repeat the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers, or all, or substantially all, or some predetermined number, or some predetermined percentage of the layers of the additively manufactured 3D printed part are printed. For example, the controller 922 or the processor 924 as shown and described in connection with FIG. 9, may provide a means for causing the apparatus to repeat the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers, or all, or substantially all, or some predetermined number, or some predetermined percentage of the layers of the additively manufactured 3D printed part are printed.

[0130] FIG. 1 1 is a flow chart illustrating an example process 1100 (e.g., a method) of metal 3D printing utilizing additive manufacturing and an electron beam melting processin accordance with some aspects of the disclosure. As described below, some or all illustrated features may be omitted in a particular implementation within the scope of the present disclosure, and some illustrated features may not be required for implementation of all examples. In some examples, the process 1 100 may be carried out by an apparatus having a controller, a memory coupled to the controller, a multi-axis tilt and rotation platform coupled to the controller, and a heat source coupled to the controller. The multiaxis tilt and rotation platform may be configured to securely receive a part manufactured using an additive manufacturing electron beam melting process, the part having a single crystal core and an outer polycrystalline shell. The apparatus may be further configured to translate the part along an X-axis, a Y-axis, and a Z-axis and rotate the part around the X-axis, the Y-axis, and the Z-axis. The apparatus may be further configured to orient the part to expose the outer polycrystalline shell to the heat source. In some examples, the process 1 100 may be carried out by any suitable apparatus or means for carrying out the functions or algorithm described below.

[0131] At block 1102, the apparatus may securely receive a part manufactured using an additive manufacturing electron beam melting process, the part having a single crystal core and an outer polycrystalline shell.

[0132] At block 1 104, the apparatus may remove unmelted metal powder from the outer polycrystalline shell.

[0133] At block 1 106, the apparatus may apply heat to the outer polycrystalline shell to re-melt the outer polycrystalline shell, the re-melting converting the polycrystalline shell into a single crystal having a same orientation as the single crystal core.

[0134] FIG. 12 illustrates one example of a process 1200 (e.g., a method), alongside a cross-section of a first body 1202 (which is a solid body) and a cross-section of second body 1204 (which includes internal spaces defined by internal side walls of the second body 1204) (e.g., internal channels, passages, etc.) according to some aspects of the disclosure. The first body 1202 and the second body 1204 are shown before 1212 PX removal and after 1214 PX removal. According to some aspects, a PX shell may be removed in situ by a combination of machining, and / or removing or displacing metal powder, and / or remelting to convert the PX to SX. According to some aspects, the PX shell of a body (e.g., first body 1202, second body 1204, a 3D printed object) may be removed in situ by a process of remelting to convert PX to SX (e.g., using the heat source used to fabricate each layer or another heat source) and / or ex situ by a process ofmelting / remelting to convert PX to SX (e.g., using the heat source used to melt each layer or another heat source) after the part is printed. The preceding processes are exemplary and non-limiting. At block 1206, a layer, N, may be printed. See, for example, the first body 1202 and the second body 1204 before 1212 PX removal. At block 1208, a system (e.g., the system 901 , as shown and described in connection with FIG. 9) may perform an in situ process of PX removal. As a result, only SX remains at block 1210 after 1214 PX removal at block 1208. Aspects described and exemplified herein may yield the SX result observed at block 1210 at both the exterior of the first body 1202 and the exterior and interior (e.g., within the internal spaces defined by internal side walls) of the second body 1204.

[0135] Of course, in the above examples, the circuitry included in the processor 924 of FIG. 9 is merely provided as an example. Other means for carrying out the described processes or functions may be included within various aspects of the present disclosure, including but not limited to the instructions 929 stored in / on the memory I computer- readable medium 928 of FIG. 9 or any other suitable apparatus or means described in any one of FIGs. 1 , 2, 3, 4, 9, and / or 12 utilizing, for example, the processes and / or algorithms described herein in relation to any one of FIGs. 5, 6, 7, 8, 10, 1 1 , and / or 12.

[0136] Several aspects of 3D printing systems have been presented with reference to exemplary implementations. As those persons having ordinary skill in the art will readily appreciate, various aspects described throughout this disclosure may be extended to other 3D printing systems.

[0137] The following provides an overview of aspects of the present disclosure.

[0138] Aspect 1 : A method of additively manufacturing a three-dimensional (3D) printed part, comprising: spreading a layer of an unmelted metal powder on a powder bed; melting a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of the additively manufactured 3D printed part; repeating the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder; displacing, utilizing a tool, the unmelted metal powder adjacent to a first edge of the shape; re-melting the first edge of the shape; and repeating the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers of the additively manufactured 3D printed part are printed.

[0139] Aspect 2: The method of aspect 1 , further comprising: performing the melting and the re-melting with an electron beam.

[0140] Aspect 3: The method of aspect 1 or aspect 2, further comprising: displacing, utilizing the tool, the unmelted metal powder adjacent to the first edge to a predetermined depth relative to a presently printed uppermost surface of the additively manufactured 3D printed part.

[0141] Aspect 4: The method of any of aspects 1 through 3, wherein the tool is at least one of: a suction device, a combined suction and gas jet device, a displacement member, a cylinder, a rotating spindle, an auger, or a spiral shaft.

[0142] Aspect 5: The method of any of aspects 1 through 4, further comprising: spreading the layer of the unmelted metal powder on the powder bed utilizing a recoater head; and displacing, utilizing the tool, the unmelted metal powder adjacent to the first edge of the shape comprises: positioning the tool adjacent to the first edge of the shape utilizing a tool actuator coupled to the recoater head.

[0143] Aspect 6: The method of any of aspects 1 through 5, wherein the additively manufactured 3D printed part, prior to the re-melting, includes: a preexisting single crystal metal core; a single crystal metal zone surrounding the preexisting single crystal metal core, the single crystal metal zone formed in an outward direction relative to the preexisting single crystal metal core and formed via nucleation upon the preexisting single crystal metal core; and a polycrystalline metal zone surrounding the single crystal metal zone, the polycrystalline metal zone formed in an inward direction toward the single crystal metal zone and formed via nucleation upon the unmelted metal powder, wherein the first edge corresponds to a projection of a final outer wall of the additively manufactured 3D printed part on the layer of the unmelted metal powder.

[0144] Aspect 7: The method of aspect 6, wherein the first edge surrounds the additively manufactured 3D printed part and includes at least one of: single crystal metal, or polycrystalline metal.

[0145] Aspect 8: The method of any of aspects 1 through 7, wherein the re-melting the first edge forms a second edge that is devoid of polycrystalline metal.

[0146] Aspect 9: An apparatus, comprising: means for spreading a layer of an unmelted metal powder on a powder bed; means for melting a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part; means for repeating the spreadingand the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder; means for displacing the unmelted metal powder adjacent to a first edge of the shape; means for re-melting the first edge of the shape; and means for repeating the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers of the additively manufactured 3D printed part are printed.

[0147] Aspect 10: The apparatus of aspect 9, wherein the means for displacing the unmelted metal powder adjacent to the first edge displaces the unmelted metal powder to a predetermined depth relative to a presently printed uppermost surface of the additively manufactured 3D printed part.

[0148] Aspect 11 : The apparatus of aspect 9 or aspect 10, wherein the means for displacing is at least one of: a suction device, a combined suction and gas jet device, a displacement member, a cylinder, a spindle, an auger, or a spiral shaft.

[0149] Aspect 12: The apparatus of any of aspects 9 through 1 1 , wherein: the means for spreading is a recoater head; and the means for displacing is positioned adjacent to the first edge of the shape utilizing the tool actuator coupled to the recoater head.

[0150] Aspect 13: The apparatus of any of aspects 9 through 11 , wherein the additively manufactured 3D printed part, prior to the re-melting, includes: a preexisting single crystal metal core; a single crystal metal zone surrounding the preexisting single crystal metal core, the single crystal metal zone formed in an outward direction relative to the preexisting single crystal metal core and formed via nucleation upon the preexisting single crystal metal core; and a polycrystalline metal zone surrounding the single crystal metal zone, the polycrystalline metal zone formed in an inward direction toward the single crystal metal zone and formed via nucleation upon the unmelted metal powder, wherein the first edge corresponds to a projection of a final outer wall of the additively manufactured 3D printed part on the layer of the unmelted metal powder.

[0151] Aspect 14: The apparatus of aspect 13, wherein the first edge surrounds the additively manufactured 3D printed part and includes at least one of: single crystal metal, or polycrystalline metal.

[0152] Aspect 15: The apparatus of any of aspects 9 through 14, wherein the re-melting the first edge forms a second edge that is devoid of polycrystalline metal.

[0153] Aspect 16: A non-transitory computer-readable medium storing instructions that when executed by a processing circuit cause the processing circuit to cause an apparatusand / or tool to: spread a layer of an unmelted metal powder on a powder bed; melt a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part; repeat the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder; displace, utilizing a tool, the unmelted metal powder adjacent to a first edge of the shape; re-melt the first edge of the shape; and repeat the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers of the additively manufactured 3D printed part are printed.

[0154] Aspect 17: The non-transitory computer-readable medium of aspect 16, further storing instructions that when executed by the processing circuit cause the processing circuit to cause the apparatus to displace, utilizing the tool, the unmelted metal powder adjacent to the first edge to a predetermined depth relative to a presently printed uppermost surface of the additively manufactured 3D printed part.

[0155] Aspect 18: The non-transitory computer-readable medium of aspect 16 or aspect 17, wherein the tool is at least one of: a suction device, a combined suction and gas jet device, a displacement member, a cylinder, a spindle, an auger, or a spiral shaft.

[0156] Aspect 19: An apparatus, comprising: a powder bed; an electron beam gun focused on the powder bed; a recoater head configured to recoat the powder bed with a layer of an unmelted metal powder; a tool actuator coupled to the recoater head; a tool coupled to the tool actuator, wherein the apparatus is configured to: spread, utilizing the recoater head, the layer of the unmelted metal powder on the powder bed; melt, utilizing the electron beam gun, a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part; repeat the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder; displace, utilizing the tool coupled to the tool actuator coupled to the recoater head, the unmelted metal powder adjacent to a first edge of the shape; remelt, utilizing the electron beam gun, the first edge of the shape; and repeat the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers of the additively manufactured 3D printed part are printed.

[0157] Aspect 20: The apparatus of aspect 19, wherein the apparatus is further configured to: displace, utilizing the tool, the unmelted metal powder adjacent to the firstedge to a predetermined depth relative to a presently printed uppermost surface of the additively manufactured 3D printed part.

[0158] Aspect 21 : The apparatus of aspect 19 or aspect 20, wherein the tool is at least one of: a suction device, a combined suction and gas jet device, a displacement member, a cylinder, a spindle, an auger, a spiral shaft.

[0159] Aspect 22: The apparatus of any of aspects 19 through 21 , further comprising: spreading the layer of the unmelted metal powder on the powder bed utilizing the recoater head; and displacing, utilizing the tool, the unmelted metal powder adjacent to the first edge of the shape comprises: positioning the tool adjacent to the first edge of the shape utilizing the tool actuator coupled to the recoater head.

[0160] Aspect 23: The apparatus of any of aspects 19 through 22, wherein the additively manufactured 3D printed part, prior to the re-melting, includes: a preexisting single crystal metal core; a single crystal metal zone surrounding the preexisting single crystal metal core, the single crystal metal zone formed in an outward direction relative to the preexisting single crystal metal core and formed via nucleation upon the preexisting single crystal metal core; and a polycrystalline metal zone surrounding the single crystal metal zone, the polycrystalline metal zone formed in an inward direction toward the single crystal metal zone and formed via nucleation upon the unmelted metal powder, wherein the first edge corresponds to a projection of a final outer wall of the additively manufactured 3D printed part on the layer of the unmelted metal powder.

[0161] Aspect 24: The apparatus of aspect 23, wherein the first edge surrounds the additively manufactured 3D printed part and includes at least one of: single crystal metal, or the polycrystalline metal.

[0162] Aspect 25: The apparatus of any of aspects 19 through 24, wherein the remelting the first edge forms a second edge that is devoid of polycrystalline metal.

[0163] Aspect 26: A system, comprising: one or more processors; one or more memories coupled to the one or more processors; a powder bed; an electron beam gun focused on the powder bed and coupled to the one or more processors; a recoater head coupled to the one or more processors; a tool actuator coupled to the recoater head and the one or more processors; a tool coupled to the tool actuator, the one or more processors being configured to, individually or collectively, based at least in part on information stored in the one or more memories: spread, utilizing the recoater head, a layer of an unmelted metal powder on the powder bed; melt, utilizing an electron beamemitted by the electron beam gun, a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part; repeat the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder; displace, utilizing the tool coupled to the tool actuator coupled to the recoater head, the unmelted metal powder adjacent to a first edge of the shape; re-melt, utilizing the electron beam gun, the first edge of the shape; and repeat the spreading, the melting, the repeating, the displacing, and the re-melting until the plurality of layers of the additively manufactured 3D printed part are printed.

[0164] Aspect 27: The system of aspect 26, wherein the one or more processors are further configured to, individually or collectively, based at least in part on information stored in the one or more memories: displace, utilizing the tool, the unmelted metal powder adjacent to the first edge to a predetermined depth relative to a presently printed uppermost surface of the additively manufactured 3D printed part.

[0165] Aspect 28: The system of aspect 26 or aspect 27, wherein the tool is at least one of: a suction device, a combined suction and gas jet device, a displacement member, a cylinder, a spindle, an auger, a spiral shaft.

[0166] Aspect 29: The system of any of aspects 26 through 28, wherein the additively manufactured 3D printed part, prior to the re-melting, includes: a preexisting single crystal metal core, a single crystal metal zone surrounding the preexisting single crystal metal core, the single crystal metal zone formed in an outward direction relative to the preexisting single crystal metal core and formed via nucleation upon the preexisting single crystal metal core, and a polycrystalline metal zone surrounding the single crystal metal zone, the polycrystalline metal zone formed in an inward direction toward the single crystal metal zone and formed via nucleation upon the unmelted metal powder, wherein the first edge corresponds to a projection of a final outer wall of the additively manufactured 3D printed part on the layer of the unmelted metal powder.

[0167] Aspect 30: The system of aspect 29, wherein the first edge surrounds the additively manufactured 3D printed part and includes at least one of: single crystal metal, or the polycrystalline metal.

[0168] Aspect 31 : The system of any of aspects 26 through 30, wherein the re-melting the first edge forms a second edge that is devoid of polycrystalline metal.

[0169] Aspect 32: A method of additively manufacturing a three-dimensional (3D) printed part, comprising: fabricating, using an electron beam melting additive manufacturing process, the 3D printed part; removing the unmelted metal powder from exterior surfaces of the 3D printed part; and converting polycrystalline metal encasing the 3D printed part to single crystal metal.

[0170] Aspect 33: The method of aspect 32, further comprising: converting the polycrystalline metal encasing the 3D printed part to the single crystal metal by re-melting the polycrystalline metal to a depth corresponding to a surface of a single crystal metal core of the 3D printed part.

[0171] Aspect 34: The method of aspect 33, wherein the re-melting is accomplished using at least one of: a laser, and electron beam, a flame, or an induction heater.

[0172] Aspect 35: A method of converting an outer polycrystalline shell of an additively manufactured three-dimensional (3D) printed part into a single crystal, comprising: securely receiving the additively manufactured 3D printed part, the part additively manufactured using an electron beam melting process, the part having a single crystal core and the outer polycrystalline shell; removing unmelted metal powder from the outer polycrystalline shell; and applying heat to the outer polycrystalline shell to re-melt the outer polycrystalline shell, the re-melting converting the outer polycrystalline shell into the single crystal having a same orientation as the single crystal core.

[0173] One or more of the components, steps, features, and / or functions illustrated in FIGs. 1 -12 may be rearranged and / or combined into a single component, step, feature, or function or embodied in several components, steps, or functions. Additional elements, components, steps, and / or functions may also be added without departing from novel features disclosed herein. The apparatus, devices, and / or components illustrated in FIGs. 1 -12 may be configured to perform one or more of the methods, features, or steps described herein. The novel algorithms described herein may also be efficiently implemented in software and / or embedded in hardware.

[0174] It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based on design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The method claims present elements of the various steps in a sample order and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein.

[0175] The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein but are to be accorded the full scope consistent with the language of the claims, wherein the reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more” or “at least one.” Unless specifically stated otherwise, the term “some” refers to one or more.

[0176] Various modifications to the examples described in this disclosure may be readily apparent to persons having ordinary skill in the art, and the generic principles defined herein may be applied to other examples without departing from the spirit or scope of this disclosure. Thus, the claims are not intended to be limited to the examples shown herein but are to be accorded the widest scope consistent with this disclosure, the principles, and the novel features disclosed herein.

[0177] Additionally, various features that are described in this specification in the context of separate examples can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple examples separately or in any suitable subcombination. As such, although features may be described above as acting in particular combinations, and even initially claimed as such, one or more features from a claimed combination can, in some cases, be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0178] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order or that all illustrated operations be performed to achieve desirable results. Further, the drawings may schematically depict one or more example processes in the form of a flowchart or flow diagram. However, other operations that are not depicted can be incorporated into the schematically illustrated example processes. For example, one or more additional operations can be performed before, after, simultaneously, or between any of the illustrated operations. In some circumstances, multitasking and parallel processing may be advantageous.

Claims

CLAIMSWhat is claimed is:1 . A method of additively manufacturing a three-dimensional (3D) printed part, comprising: spreading a layer of an unmelted metal powder on a powder bed; melting a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of the additively manufactured 3D printed part; repeating the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder; displacing, utilizing a tool, the unmelted metal powder adjacent to a first edge of the shape; re-melting the first edge of the shape; and repeating the spreading, the melting, the repeating, the displacing, and the remelting until the plurality of layers of the additively manufactured 3D printed part are printed.

2. The method of claim 1 , further comprising: displacing, utilizing the tool, the unmelted metal powder adjacent to the first edge to a predetermined depth relative to a presently printed uppermost surface of the additively manufactured 3D printed part.

3. The method of claim 1 , wherein the tool is at least one of: a suction device, a combined suction and gas jet device, a displacement member, a rotating spindle, an auger, or a spiral shaft.

4. The method of claim 1 , further comprising: spreading the layer of the unmelted metal powder on the powder bed utilizing a recoater head; and displacing, utilizing the tool, the unmelted metal powder adjacent to the first edge of the shape comprises:positioning the tool adjacent to the first edge of the shape utilizing a tool actuator coupled to the recoater head.

5. The method of claim 1 , wherein the additively manufactured 3D printed part, prior to the re-melting, includes: a preexisting single crystal metal core; a single crystal metal zone surrounding the preexisting single crystal metal core, the single crystal metal zone formed in an outward direction relative to the preexisting single crystal metal core and formed via nucleation upon the preexisting single crystal metal core; and a polycrystalline metal zone surrounding the single crystal metal zone, the polycrystalline metal zone formed in an inward direction toward the single crystal metal zone and formed via nucleation upon the unmelted metal powder, wherein the first edge corresponds to a projection of a final outer wall of the additively manufactured 3D printed part on the layer of the unmelted metal powder.

6. The method of claim 5, wherein the first edge surrounds the additively manufactured 3D printed part and includes at least one of: single crystal metal, or polycrystalline metal.

7. The method of claim 1 , wherein the re-melting the first edge forms a second edge that is devoid of polycrystalline metal.

8. An apparatus, comprising: a powder bed; an electron beam gun focused on the powder bed; a recoater head configured to recoat the powder bed with a layer of an unmelted metal powder; a tool actuator coupled to the recoater head; a tool coupled to the tool actuator, wherein the apparatus is configured to: spread, utilizing the recoater head, the layer of the unmelted metal powder on the powder bed;melt, utilizing the electron beam gun, a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part; repeat the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder; displace, utilizing the tool coupled to the tool actuator coupled to the recoater head, the unmelted metal powder adjacent to a first edge of the shape; re-melt, utilizing the electron beam gun, the first edge of the shape; and repeat the spreading, the melting, the repeating, the displacing, and the remelting until the plurality of layers of the additively manufactured 3D printed part are printed.

9. The apparatus of claim 8, wherein the apparatus is further configured to: displace, utilizing the tool, the unmelted metal powder adjacent to the first edge to a predetermined depth relative to a presently printed uppermost surface of the additively manufactured 3D printed part.

10. The apparatus of claim 8, wherein the tool is at least one of: a suction device, a combined suction and gas jet device, a displacement member, a spindle, an auger, a spiral shaft.1 1 . The apparatus of claim 8, further comprising: spreading the layer of the unmelted metal powder on the powder bed utilizing the recoater head; and displacing, utilizing the tool, the unmelted metal powder adjacent to the first edge of the shape comprises: positioning the tool adjacent to the first edge of the shape utilizing the tool actuator coupled to the recoater head.

12. The apparatus of claim 8, wherein the additively manufactured 3D printed part, prior to the re-melting, includes: a preexisting single crystal metal core; a single crystal metal zone surrounding the preexisting single crystal metal core, the single crystal metal zone formed in an outward direction relative to the preexisting single crystal metal core and formed via nucleation upon the preexisting single crystal metal core; and a polycrystalline metal zone surrounding the single crystal metal zone, the polycrystalline metal zone formed in an inward direction toward the single crystal metal zone and formed via nucleation upon the unmelted metal powder, wherein the first edge corresponds to a projection of a final outer wall of the additively manufactured 3D printed part on the layer of the unmelted metal powder.

13. The apparatus of claim 12, wherein the first edge surrounds the additively manufactured 3D printed part and includes at least one of: single crystal metal, or polycrystalline metal.

14. The apparatus of claim 8, wherein the re-melting the first edge forms a second edge that is devoid of polycrystalline metal.

15. A system, comprising: one or more processors; one or more memories coupled to the one or more processors; a powder bed; an electron beam gun focused on the powder bed and coupled to the one or more processors; a recoater head coupled to the one or more processors; a tool actuator coupled to the recoater head and the one or more processors; a tool coupled to the tool actuator, the one or more processors being configured to, individually or collectively, based at least in part on information stored in the one or more memories: spread, utilizing the recoater head, a layer of an unmelted metal powder on the powder bed;melt, utilizing an electron beam emitted by the electron beam gun, a portion of the layer of the unmelted metal powder into a shape of a cross-section of a corresponding layer of a plurality of layers of an additively manufactured 3D printed part; repeat the spreading and the melting of at least one of: a next layer of the unmelted metal powder, or a predetermined plurality of next layers of the unmelted metal powder; displace, utilizing the tool coupled to the tool actuator coupled to the recoater head, the unmelted metal powder adjacent to a first edge of the shape; re-melt, utilizing the electron beam gun, the first edge of the shape; and repeat the spreading, the melting, the repeating, the displacing, and the remelting until the plurality of layers of the additively manufactured 3D printed part are printed.

16. The system of claim 15, wherein the one or more processors are further configured to, individually or collectively, based at least in part on information stored in the one or more memories: displace, utilizing the tool, the unmelted metal powder adjacent to the first edge to a predetermined depth relative to a presently printed uppermost surface of the additively manufactured 3D printed part.

17. The system of claim 15, wherein the tool is at least one of: a suction device, a combined suction and gas jet device, a displacement member, a spindle, an auger, a spiral shaft.

18. The system of claim 15, wherein the additively manufactured 3D printed part, prior to the re-melting, includes: a preexisting single crystal metal core; a single crystal metal zone surrounding the preexisting single crystal metal core, the single crystal metal zone formed in an outward direction relative to the preexisting single crystal metal core and formed via nucleation upon the preexisting single crystal metal core; and a polycrystalline metal zone surrounding the single crystal metal zone, thepolycrystalline metal zone formed in an inward direction toward the single crystal metal zone and formed via nucleation upon the unmelted metal powder, wherein the first edge corresponds to a projection of a final outer wall of the additively manufactured 3D printed part on the layer of the unmelted metal powder.

19. The system of claim 18, wherein the first edge surrounds the additively manufactured 3D printed part and includes at least one of: single crystal metal, or polycrystalline metal.

20. The system of claim 15, wherein the re-melting the first edge forms a second edge that is devoid of polycrystalline metal.

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