Healing of polycrystalline layers

Abstract

Additive manufacturing of single crystalline materials generate a polycrystalline layer or grains, which can be reduced or eliminated by treatment with Al or optionally Pt. Reduction of the polycrystalline layer can be performed without mechanical or chemical removal of the polycrystalline material. A workpiece form by this process can include a single crystalline substrate; an interdiffusion zone over the substrate; and a thermal barrier coat over the interdiffusion zone, and the interdiffusion zone diffuses the polycrystalline layer such that there is no need for post-processing needed to remove the polycrystalline layer.

Description

HEALING OF POLYCRYSTALLINE LAYERSThis application claims priority of U.S. Provisional Application 63 / 539,929, entitled “HEALING OF POLYCRYSTALLINE LAYERS,” filed September 22, 2023, the entire contents of which are incorporated by reference.TECHNICAL FIELD

[0001] Embodiments are generally related to the healing of polycrystalline (PX) layers generated during the additive manufacturing of objects formed from superalloys or steel.BACKGROUND

[0002] The production of high strength and thermally resistant single crystalline (SX) workpieces, such as turbine blades for aerospace applications, has traditionally been performed using the Bridgman process. The Bridgman technique involves slow cooling of a molten material by moving its container from a hot zone into a cold one. To facilitate the crystal growth, the end of the container where a crystal starts to grow may be elongated, and a seed crystal can be placed at that end. The presence of the seed crystal requires precise temperature control at the interface, and in many cases crystal growth is done without a seed crystal. In the original Bridgman technique, the cold zone is the outside of the furnace, and thus the temperature gradient is not well defined.

[0003] The Bridgman technique uses a “hot” and “cold” zone to create a temperature difference within a furnace as shown in FIG. 1. The hot zone 10 is kept at a temperature above the melting point of the material 20. With superalloys, the metal is molten in a separate crucible (not shown). Once the metal is at the correct temperature, and the mold 30 is at the correct temperature, the molten metal is poured into the mold. The mold has a predefined shape which is the desired shape of the end-use component. The precursor material is a melt in the hot zone 10 and translated into the cold zone 50 by motion. The material solidifies i40 as it moves through the temperature gradient in the furnace. The Bridgman method can be performed in vertical configurations.

[0004] A modified Bridgman method, known as the Bridgman-Stockbarger technique, has two well controlled temperature zones, which is achieved by employing two separate furnaces with a baffle in-between. Some variants of the Bridgman and Bridgman- Stockbarger techniques include rotation of the container and horizontal arrangement of the furnace / s. The important considerations during the crystal growth are the mold material, temperature of the hot zone, temperature gradient, and cooling rate. The container should have minimal reactivity with the sample and withstand the temperature and ambient environment during the growth.

[0005] In recent years there has been a great deal of interest in manufacturing SX parts such as turbine blades utilizing additive manufacturing (AM), a modified form of 3-D printing. A diagram of the additive manufacturing process is shown in FIG. 2.

[0006] In FIG. 2 a powder feeder 110 deposits powder 112 to produce a powder layer 105 in a powder bed 108. The powder layer that is deposited first can lie directly on the powder bed or on a substrate that may be placed in the powder bed before the powder layers are deposited. A beam scanner 101 can move a beam source 102 or steer an energy beam 1 11 that is produced by the beam source. The energy beam may be a laser beam, an electron beam, etc. The energy beam 111 produces a melt pool 104 where the energy beam 1 1 1 melts some of the powder in the powder bed 108. The melt pool 104 has a melt pool depth 103. The melt pool depth 103 is illustrated as being large enough to also melt some of the patterned layer 106 directly underneath the powder layer 105. The beam scanner moves the melt pool 104 in a path through the topmost powder layer to selectively melt some of the powder and thereby produce a patterned layer. The powder layer that is deposited first becomes the bottom patterned layer 107. A 3D object is printed by iteratively depositing a powder layer and using the energy beam to melt a pattern into that powder layer, thereby producing a patterned layer.

[0007] FIG. 3 is a high level conceptual diagram that illustrates a scan pattern 200 with a melt pool 104 and a hatch distance 203, according to some aspects. The scan pattern 200 can include a large number of scan lines 201 that may be parallel to one another as shown in FIG. 3. The hatch distance 203 is the distance between the scan lines 201. The hatchdirection is the direction from a previous scan line to a subsequent scan line in the scan pattern. The hatch direction 204 can be perpendicular to the scan lines 201. The beam scanner moves the melt pool 104 along the scan pattern. For simplicity, the melt pool is shown as a circle where the energy beam 11 1 meets the powder layer and melts the powder at that location. In practice, the melt pool is much longer because the energy beam melts material in a pattern and melted material remains melted for a short period of time.

[0008] That is, laser powder bed fusion AM of metals such as steel and nickel superalloys is conducted in a protective chamber with dynamic inert gas, e.g., argon or nitrogen, flow to avoid oxidation or gas dissolution and to remove weld byproducts such as soot and spatter. To melt specific locations, a laser beam or electron beam is scanned on top of the powder bed with different focal size and power. The absorption of laser beam leads to melting of the powder in the ith layer and also some remelting of the (i-1 )th solid layer. The dynamics of melting and the melt-pool shapes are dictated by the scan strategy in the x-y plane. As the building progresses in the z-direction with pre-determined geometrical cross-sections, one may observe the evolution of porosity, cracks, solidification grain structures, solid-state transformations, and plastic deformations. In turn, all the above physical phenomena lead to spatial variations of microstructure and properties. Moreover, there may not be a uniform single crystallinity of the resulting workpiece and polycrystalline granules or even polycrystalline border layers may be present.

[0009] Accordingly, there is a need in the art for additive manufacturing of single crystalline metal products with a reduced amount of defects including polycrystalline defects.BRIEF SUMMARY

[0010] The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole.

[0011] It is, therefore, one aspect of the disclosed embodiments to minimize or eliminate the polycrystalline shell that is a byproduct of the additive manufacture of single crystalline (SX) metallic components.

[0012] In the disclosure, a workpiece formed by additive manufacturing can include a single crystalline substrate and an interdiffusion zone (IDZ) over the substrate, the interdiffusion zone comprising the same material as the single crystalline substrate plus an amount of at least one of Al or Pt.

[0013] The interdiffusion zone is about 1 to 200 pm in thickness or 1 to 20 pm in thickness. The interdiffusion zone can include a [3 phase (body-centered cubic). The workpiece may include a thermal barrier coat formed from a ceramic. The thermal barrier coat may be a ceramic comprising yttria-stabilized zirconia. The thermal barrier coat may be a ceramic comprising yttria-stabilized zirconia containing about 4-7 % by weight yttria. The substrate may be a nickel alloy

[0014] In the disclosure, a process to manufacture a workpiece may include forming a single crystal substrate by additive manufacturing, and treating the polycrystalline layer with at least one of Al or Pt to form an interdiffusion zone.

[0015] The treating the polycrystalline layer may be performed by vapor phase aluminide to form a nickel aluminide comprising at least one of NisAI, Ni Al or NiAh. the treating the polycrystalline layer is performed by vapor phase aluminide to yield a thickness of the interdiffusion zone of about 1 to 200 pm or about 1 to 20 pm. The interdiffusion zone may include a p phase.

[0016] In the disclosure, the single crystalline substrate if formed by successive steps of: depositing a powder coating of metal, and melting the powder coating. The polycrystalline layer may not be reduced by mechanical abrading or chemical treatment. Alternatively, the polycrystalline layer may not be reduced by mechanical abrading or chemical treatmentbefore or after treating the polycrystalline layer with at least one of Al or Pt.

[0017] The process of the disclosure may further include forming a thermal bonding coat over the interdiffusion zone, the thermal bonding coat comprising at least one material selected from titania, zirconia, alumina, porcelain, porcelainite, pyrochlores, garnets, monazite, perovskites or lanthanum magnesium hexa-aluminate.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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 embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein.

[0019] FIG. 1 depicts formation of a single crystal workpiece by the Bridgman process.

[0020] FIG. 2 depicts the formation of a single crystal workpiece by additive manufacturing.

[0021] FIG. 3 is a conceptual diagram that illustrates a scan pattern with a melt pool

[0022] FIG. 4 is a graph of creep rupture of Rene alloys.

[0023] FIG. 5 shows electron photomicrographs of a single crystalline workpiece.

[0024] FIG. 6 shows an electron photomicrograph of a single crystalline workpiece with a polycrystalline layer.

[0025] FIG. 7 shows an expected cross sectional electron photomicrograph of a workpiece according to the disclosure.DETAILED DESCRIPTION

[0026] The particular values and configurations discussed in the following non-limiting examples can be varied and are cited merely to illustrate one or more embodiments and are not intended to limit the scope thereof.

[0027] Example embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments are shown. The embodiments disclosed herein can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the embodiments to those skilled in the art. Like numbers refer to like elements throughout.

[0028] The terminology used herein is for the purpose of describing particular embodiments 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 indicates otherwise. 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.

[0029] 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 embodiment” as used herein does not necessarily refer to the same embodiment and the phrase “in another embodiment” as used herein does not necessarily refer to a different embodiment. It is intended, for example, that claimed subject matter include combinations of example embodiments in whole or in part.

[0030] 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.

[0031] It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, kit, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

[0032] It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

[0033] 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.

[0034] 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.

[0035] 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 orterms in any combination, unless otherwise apparent from the context.

[0036] All of the compositions and / or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and / or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the invention. 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 invention as defined by the appended claims.

[0037] It is, therefore, one aspect of the disclosed embodiments to minimize or eliminate the polycrystalline shell that is a byproduct of the additive manufacture (AM) of single crystalline (SX) metallic components.

[0038] Among the materials used in AM are the single-crystal nickel superalloys, due to their high temperature performance and tendency to form heat resistant phases when treated with Al or optionally Pt. Of the nickel superalloys, the p crystal structure is typically body-centered cubic (BCC) austenitic. Examples of such alloys are Hastelloy, Inconel, Waspaloy, Rene alloys, Incoloy, MP98T, TMS alloys, and CMSX single crystal alloys.

[0039] Conventional nickel superalloys are typified by the Rene alloys such as Rene N5 or Rene 125. A typical formulation of these types of alloys is set forth in Table 1 .Table 1. Typical Alloy Compositions.

[0040] Among the Hastelloys, Hastelloy C22 has a composition (wt%) of 56% Ni, 22% Cr and 13% Mo, with additions of iron, tungsten, and cobalt. Hastelloy C-276 has a composition (wt%) of 57% Ni, 15-17% Mo, 14.5-16.5% Cr, 4-7% Fe, 3-4,5% W, 1 $ max Mn, 2.5% max Co, 0.35% max V and 0.08% max Si. Among the Inconels, Inconel 600 has 72% Ni, 14-17% Cr, 6-10$ Fe and 1% Mn with traces of Cu, Si, C and S.

[0041] During the AM process, the ith layer can be melted by either an electron beam or a laser beam following deposition of the powder of the ith layer. If an electron beam is used for melting, the ith layer, the median particle size of the nickel alloy ranges from about 40 to 105 pm. If a laser beam is used to melt the ith layer, the median particle size can range from about 15 to 55 pm. The i-1 th layer serves as a seed crystal to render the ith layer an SX layer.

[0042] The body-centered cubic |3 phase or face-centered cubic y’ phase is formed from Nis(AI,Ti). With Ti not being present to an appreciable degree, the y’ phase is formed from NiaAL The properties of the alloy are highly dependent on the p or y’ phase. FIG. 4 is a graph showing creep rupture of Rene-type alloys as a function of the volume fraction of y’ phase. As can be seen, the creep rupture life reaches a maximum at about 60% to 70% y’ phase. As the y’ phase increases or decreases from this maximum, even a 10% increase or decrease in y’ phase will result in a reduction of creep rupture life of an order of magnitude on the logarithmic scale. The y' phase is largely responsible for the elevated-temperature strength of the material and its incredible resistance to creep deformation.

[0043] The process of creating single crystal (SX) metal materials by additive manufacturing may create a polycrystalline (PX) shell. The PX shell is not desired and requires removal to continue to process the single crystal. FIG. 5 shows electron photomicrographs of a single SX nickel alloy formed by additive manufacturing, which has been post-processed to remove or reduce the PX shell. The PX domain (vertical line on theelectron photomicrographs at the right) has been mechanically or chemically reduced before the Thermal Barrier Coating (TBC) is applied.

[0044] The residual PX shell can be seen in the electron photomicrograph shown in FIG. 6. As can be seen, a PX shell layer is formed at both edges of the body of the workpiece, this PX shell being an unwanted artifact of the fusing process using an electron beam or a laser beam. The PX shell has a width of about 0 mm to 2 mm (up to 2000 pm) or about 0.1 mm to 2 mm (100 pm to 2000 pm), and can be in the range of about 1 mm to 2 mm (1000 pm to 2000 pm). The faint striations in the SX center are deformations arising from the AM layering process.

[0045] Processing of the workpiece can include a range of techniques. These techniques are, but are not restricted to, Vapor Phase Aluminide (VPA), Platinum Aluminide (PtAI), Thermal Barrier Coating (TBC), Chemical Vapor Deposition (CVD) aluminizing, other CVD processes, hydrogen reduction of vapor-phase mixtures of NiCh and AICIs, electron-beam physical vapor deposition (EB-PVD), sputtering (of Al, Ni-rich alloy, or other materials), molecular-beam epitaxy (MBE), thermal annealing, laser annealing, mechanical polishing, chemical polishing, passivation (i.e., anodizing), acid etching, etc., which are utilized to increase the temperature capabilities of materials.

[0046] For example, following the VPA or PtAI processing the resulting IDZ has a thickness of about 1 to 200 pm in thickness, and can be 0 to 20 pm or 1 to 20 pm. This reduced thickness eliminates the need to remove the PX layer by mechanical or chemical methods, thus removing this step before further processing.

[0047] VPA or Above-the-Pack is a process where components are placed in a heated inert atmosphere, surrounded by CrAI donor material. The donor material does not contact the parts directly. During thermal processing, the aluminum in the donor material and halide activator vaporize in the presence of a carrier gas and condense onto the target parts. It then further diffuses into the substrate and combines with nickel, forming a nickel aluminide (NisAI, Ni Al or Ni Als). The resulting coating contains both a diffused and additive layer. In hot service, a durable oxide scale is formed, which protects the component from further oxidation. This VPA process can also be used to coat the internal passages of parts, such as turbine blades. Additionally, VPA can be combined with platinum plating to form platinum aluminides or with a change in donor material can be used for Vapor Phase Chromizing(VPC), both for hot corrosion resistance.

[0048] VPA is a cost-effective solution to increase hot oxidation and corrosion resistance on superalloys. It is relatively thin at an approximately 25 pm to 80 pm, and is capable of coating internal passages. VPA can be combined with other thermal barrier coating processes to further enhance protection, and can be used on a wide variety of superalloys. An additional advantage of VPA is the formation of a £ phase that is resistant to high temperatures. The [3 phase can be for example formed from Ni (Al, Ti) which have an ordered BCC structure.

[0049] A micrograph of the coating application process shows an Interdiffusion Zone (IDZ) between the TBC coating and substrate. The result of the additional processing of the workpiece is shown in FIG. 6, where the PX shell ranges from 0 mm up to 2 mm..

[0050] In the disclosure, the PX shell thickness is effectively reduced directly by VPA. The PX shell becomes part of the bond coat and IDZ and thus does not need to be post processed for removal resulting in a more economic process. That is, the PX shell created from the additive process is a “bondcoat” for the VPA / PtAI process application. However, additional processes can be performed to further reduce the PX shell thickness.

[0051] During thermal processing, the aluminum in the donor material and halide activator vaporize in the presence of a carrier gas and condense onto the target parts. It then further diffuses into the substrate and combines with nickel, forming a nickel aluminide. The resulting coating contains both a diffused and additive layer. In hot service, a durable oxide scale is formed, which protects the component from further oxidation. This VPA process can also be used to coat the internal passages of parts, such as turbine blades. Additionally, VPA can be combined with platinum plating to form platinum aluminides or with a change in donor material can be used for Vapor Phase Chromizing (VPC), both for hot corrosion resistance.

[0052] In the VPA process, Components are batch processed within large circular cans surrounded by donor material and an activator. The donor material is held in separate baskets and does not contact components directly. These cans are then loaded into a retort and placed in a furnace. Inert gas is passed through both the cans and the retort while heating to a temperature suitable to vaporize donor material. Donor vapor condenses on target parts and diffuses into substrate material. Parts are subsequently vacuum heat treated to enhance properties further.

[0053] The crack closure mechanism of the disclosure utilizes AM for single crystal creation. The polycrystalline (PX) shell or edge grains are created as part of these processes. The PX shell thickness is controlled to be thin enough to directly apply VPA or PtAI

[0054] In the disclosure, the PX shell thickness is directly controlled during AM by VPA so that the remaining PX shell incorporates directly into the IDZ, thus eliminating or reducing the need to otherwise remove the PX shell completely.

[0055] Optionally other methods may be used to reduce the PX shell thickness either before or after the VPA step. These methods can include mechanical abrading of the PX layer or a chemical treatment to dissolve a portion of the PX layer.

[0056] The workpiece is optionally capped with a Thermal Bonding or Barrier Coat (TBC), which is usually a ceramic.

[0057] Further processing of the workpiece my include Vapor Phase Aluminide (VPA), Platinum Aluminide (PtAI), and Thermal Barrier Coating (TBC), which are utilized to increase the temperature capabilities of materials. A micrograph of the coating application process results in an Interdiffusion Zone (IDZ) between the coating and substrate. The expected result of the additional processing of the workpiece is shown in the electron photomicrograph in FIG. 7.

[0058] In the cross sectional view of FIG. 7 the top bond coat is about 22 to 55 pm thick. The IDZ between the substrate and the bond coat is about 20 pm thick. This thickness range of 20 pm or less (down to 1 pm) permits the direct processing of the PX material via VPA or PtAI to yield an IDZ.

[0059] The structure is optionally capped with a Thermal Bonding Coat or Thermal Barrier Coat (TBC), as can be seen in FIG. 7, which is usually a ceramic adapted to perform well in aggressive thermal environments and to deal with thermal expansion stresses during heating and cooling, adequate porosity is needed, as well as appropriate matching of thermal expansion coefficients with the metal surface that the TBC is coating. Phase stability is required to prevent significant volume changes (which occur during phase changes), which would cause the coating to crack or spall. In air-breathing engines, oxidation resistance is necessary, as well as decent mechanical properties for rotating / moving parts or parts in contact.

[0060] In TBC, Effective thermal barrier materials should demonstrate such properties aslow thermal diffusivity, phase stability and thermal shock resistance during thermal cycling, strong adherence to the substrate, and shielding against oxidation and corrosion for both the metallic bond coat and the substrate. In general, titania, zirconia, alumina, porcelain, porcelainite, pyrochlores (A23+B24+O?), garnets (Y3AlxFe5-xOi2), monazite (LaPCU), perovskites (ABO3), lanthanum magnesium hexa-aluminate (LaMgAnO ), etc. (even diamond), have all been measured to have low thermal conductivity and can therefore be considered as potential TBC materials.

[0061] Yttria partially stabilized zirconia (YSZ) is a ceramic material seen in a wide-range of TBC applications, owing to its exceptional overall properties (e.g., relatively low thermal conductivity, high dielectric constant, excessive fracture toughness, and chemical inertness at high temperatures). Notably, YSZ has greater resistance to thermal shock than do other ceramic topcoats. The yttria stabilizer in the YSZ coating helps preserve the tetragonal phase of zirconia at room temperature, which suffers a monoclinic phase change under applied external stress. This phase change causes a volumetric expansion and, thus, a buildup of compressive stresses in the vicinity of cracks, thereby promoting transformation toughening by crack propagation. Typically about 4 to 7% yttria is present.

[0062] At peak operating conditions found in gas-turbine engines with temperatures in excess of 700 °C, oxidation of the bond-coat leads to the formation of a thermally-grown oxide (TGO) layer. Formation of the TGO layer is inevitable for many high-temperature applications, so thermal barrier coatings are often designed so that the TGO layer grows slowly and uniformly. Such a TGO will have a structure that has a low diffusivity for oxygen, so that further growth is controlled by diffusion of metal from the bond-coat rather than the diffusion of oxygen from the top-coat.

[0063] This technology is not restricted to conventional powder AM processes. It can also be used in directional solidifications (DS), powder bed fusion (PBF), electron beam melting (EBM), laser powder bed fusion (L-PBF), directed energy distribution (DED) and selective laser melting (SLM). These technologies can be used for the production of components for high pressure turbines (HPT) and low pressure turbines (LPT).

[0064] Thermal barrier coatings typically include four layers: the metal substrate, metallic bond coat, thermally-grown oxide (TGO), and ceramic topcoat. The ceramic topcoat is typically composed of yttria-stabilized zirconia (YSZ), which has very low thermal conductivitywhile remaining stable at the nominal operating temperatures typically seen in TBC applications. This ceramic layer creates the largest thermal gradient of the TBC and keeps the lower layers at a lower temperature than the surface.

[0065] All of the compositions and / or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and / or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the invention. 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 invention as defined by the appended claims.

Claims

CLAIMSWhat is claimed is:1 . A workpiece formed by additive manufacturing, comprising: a single crystalline substrate; and an interdiffusion zone over the substrate, the interdiffusion zone comprising a same material as the single crystalline substrate plus an amount of at least one of Al or Pt.

2. The workpiece of claim 1 , wherein the interdiffusion zone is about 1 to 200 pm in thickness.

3. The workpiece of claim 1 , wherein the interdiffusion zone is about 1 to 20 pm in thickness.

4. The workpiece of claim 1 , wherein the interdiffusion zone includes a p phase.

5. The workpiece of claim 1 , further comprising a thermal barrier coat formed from a ceramic.

6. The workpiece of claim 1 , further comprising a thermal barrier coat formed from a ceramic comprising yttria-stabilized zirconia.

7. The workpiece of claim 6, wherein the yttria-stabilized zirconia contains about 4 to 7 % by weight yttria.

8. The workpiece of claim 1 , wherein the substrate comprises a nickel alloy.

9. A process for manufacturing a workpiece, comprising: forming a single crystalline substrate by additive manufacturing, the single crystalline substrate having a polycrystalline layer; and treating the polycrystalline layer with at least one of Al or Pt to form an interdiffusion zone.

10. The process of claim 9, wherein the treating the polycrystalline layer is performed by vapor phase aluminide.1 1 . The process of claim 9, wherein the treating the polycrystalline layer is performed by vapor phase aluminide to form a nickel aluminide comprising at least one of NisAI, Ni Al or NiAls.

12. The process of claim 9, wherein the treating the polycrystalline layer is performed by vapor phase aluminide to yield a thickness of the interdiffusion zone of about 1 to 200 pm.

13. The process of claim 9, wherein the treating the polycrystalline layer is performed by vapor phase aluminide to yield a thickness of the interdiffusion zone of about 1 to 20 pm.

14. The process of claim 9, wherein the interdiffusion zone includes a [3 phase.

15. The process of claim 9, wherein the single crystalline substrate if formed by successive steps of: depositing a powder coating of metal; and melting the powder coating.

16. The process of claim 9, wherein the polycrystalline layer is not reduced by mechanical abrading.

17. The process of claim 9, wherein the polycrystalline layer is not reduced by chemical treatment.

18. The process of claim 9, wherein the polycrystalline layer is treated by mechanical abrading or chemical treatment before or after treating the polycrystalline layer with at least one of Al or Pt.

19. The process of claim 9, further comprising:forming a thermal bonding coat over the interdiffusion zone.

20. The process of claim 9, further comprising: forming a thermal bonding coat over the interdiffusion zone, the thermal bonding coat comprising at least one material selected from the group consisting of titania, zirconia, alumina, porcelain, porcelainite, pyrochlores, garnets, monazite, perovskites and lanthanum magnesium hexa-aluminate.

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