Molybdenum and molybdenum-based structures by electron beam additive manufacturing, in particular for the manufacture of structures for nuclear components

Abstract

A methodology and manufacturing process for manufacturing components, more particularly molybdenum or molybdenum-based alloy components, particularly of complex nuclear component geometries, by electron beam deposition modeling. Input parameters are provided to control electron beam deposition modeling equipment, such as an electron beam melter. The input parameters relate to various process steps including build setup, initial heat treatment, initial layering of powder, pre-solidification heat treatment, solidification, post-solidification heat treatment, layer indexing, and post-build heat treatment. The methodology and manufacturing process allow for the manufacture of molybdenum components having a purity of ≧99.0% and a density of ≧99.75%. Metallographic analysis cross-sections of the manufactured molybdenum components are porosity-free and crack-free.

Description

[Technical field]

[0001] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This invention was made with Government support under DOE Cooperative Agreement Number DE-NE0008744 awarded by the Department of Energy and CRADA No. NFE-19-07627 between BWXT Nuclear Energy, Inc. and UT-Battelle, LLC, the management and operation contractor for Oak Ridge National Laboratory to the U.S. Department of Energy. The Government has certain rights in this invention.

[0002] FIELD OF THE DISCLOSURE This disclosure relates generally to manufacturing methods by electron beam additive manufacturing, and more particularly, methods for manufacturing pure molybdenum and molybdenum-based structures, including structures for nuclear components, by electron beam additive manufacturing are disclosed. [Background technology]

[0003] In the following discussion, reference is made to certain structures and / or methods. However, the following reference should not be construed as an admission that these structures and / or methods constitute prior art. Applicant expressly reserves the right to show that such structures and / or methods do not qualify as prior art against the present invention.

[0004] Advanced reactor concepts, such as the GEN IV Very High Temperature Reactor (VHTR) and the GEN IV Extreme High Temperature Reactor (UHTR), continue to be investigated. Advanced manufacturing processes are being investigated to support such advanced reactor concepts. For example, one advanced manufacturing process of interest is additive manufacturing using electron beam melting technology. Advanced manufacturing processes for complex nuclear component geometries are of particular interest.

[0005] In addition, for nuclear applications, the manufacture of nuclear components having compositions that are molybdenum or molybdenum-based alloys is of interest due to the high melting point of molybdenum, for example, it can be used as a structural material for fuel elements that can contribute to improving the safety of nuclear reactors.

[0006] However, methods and manufacturing processes have not been developed to successfully manufacture nuclear components, and more particularly molybdenum or molybdenum-based alloy nuclear components, by electron beam deposition modeling. Thus, many aspects and parameters associated with advanced manufacturing processes of specific materials by specific manufacturing processes are unknown and remain barriers to the implementation of advanced manufacturing processes in this technology area. Summary of the Invention [Problem to be solved by the invention]

[0007] The present disclosure provides methods and manufacturing processes for manufacturing nuclear components, more particularly molybdenum or molybdenum-based alloy nuclear components, particularly complex nuclear component geometries, by electron beam deposition modeling, which may include input parameters for controlling electron beam deposition modeling equipment, such as electron beam melters. Variables and inputs associated with various process steps are disclosed, including build setup, initial heat treatment, initial powder layering, pre-solidification heat treatment, solidification, post-solidification heat treatment, layer indexing, and post-build heat treatment. [Means for solving the problem]

[0008] In one embodiment of a method for manufacturing a component by electron beam fused deposition modeling, the method includes a build setup step including seating a starter plate on a powder layer in a reaction zone of a vacuum chamber of an electron beam fused deposition modeling machine, the powder layer including a first powder; an initial heat treatment step including positioning the starter plate at a plate offset distance, heating the starter plate to a first temperature, holding the starter plate at the first temperature, and sintering a portion of the powder layer on which the starter plate is seated; and a step of sintering the starter plate with a base layer of the first powder. The method includes covering at least a portion of the build surface of the plate; a pre-solidification step including a first heating step in which the base layer is heated to a first pre-heat temperature and a second heating step in which the base layer is heated to a second pre-heat temperature, the second pre-heat temperature being higher than the first pre-heat temperature, the first pre-heat temperature agglomerating the first powder of the base layer and the second pre-heat temperature densifying a portion of the agglomerated first powder; a solidification step including sintering a current layer of the component from the densified portion of the agglomerated first powder; and a post-build step including a cooling step.

[0009] In some embodiments, one or both of the starter plate and powder (used in the electron beam fusion deposition modeling process) have a composition consisting of molybdenum having a purity of 99.0% or greater, such as 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, or 99.9% purity, or alternatively 99.3% or greater, or 99.5% or greater. The use of a starter plate with a composition aligned with the composition of the additive manufacturing powder was followed to minimize and / or avoid intermetallic layers that would occur if a molybdenum-based additive manufacturing powder were deposited onto a non-molybdenum-based starter plate, such as a stainless steel or titanium starter plate.

[0010] In some embodiments, the method can produce nuclear components of molybdenum or molybdenum based alloys, particularly having a density of 99.75% or greater, such as 99.75%, 99.76%, 99.77%, 99.78%, 99.79%, 99.80%, 99.81%, 99.82%, 99.83%, 99.84%, 99.85%, 99.86%, 99.87%, 99.88%, 99.89%, 99.90%, 99.91%, 99.92%, 99.93%, 99.94%, 99.95%, 99.96%, 99.97%, 99.98%, 99.99%, or 100% density. In some embodiments, the nuclear components have complex geometries, such as fuel cladding components with thin walls (≦1 mm thick, or as thin as 500 microns), twisted internal flow channels, and walls with variable thickness.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS The foregoing summary, as well as the following detailed description of the embodiments, can be better understood when read in conjunction with the appended drawings, in which: It is to be understood that the illustrated embodiments are not limited to the precise arrangements and instrumentalities shown. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of an electron beam melter showing the internal arrangement of various components. [Diagram 2] 1 is a flow chart describing basic steps in one embodiment of a method for manufacturing a component by electron beam additive manufacturing. [Diagram 3] FIG. 1 is a top view of the reaction zone, showing diagrammatically the powder bed, the densified powder, and the layer of the component being produced. [Figure 4A] 1 is an image of an exemplary molybdenum structure produced by electron beam additive manufacturing. [Figure 4B] 1 is an image of an exemplary molybdenum structure produced by electron beam additive manufacturing. [Diagram 5] 4B is a near-infrared (NIR) image of the exemplary molybdenum structure shown in FIG. 4A taken during an electron beam additive manufacturing process. [Figure 6A] 1 is a metallographic image of a first cross section (XY plane) of an exemplary molybdenum structure produced by electron beam additive manufacturing. [Figure 6B] 1 is a metallographic image of a second cross section (YZ plane) of an exemplary molybdenum structure produced by electron beam additive manufacturing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] In some instances, the dimensions of the respective components have been appropriately adjusted for clarity. For ease of viewing, in some instances, only some of the named features of the figures are labeled with reference numerals.

[0014] Electron beam melting (EBM) technology is a powder bed fusion (PBF) additive manufacturing (AM) technology that utilizes a highly powdered electron beam to selectively sinter and melt metal powder layer by layer, ultimately creating a fully dense three-dimensional part. FIG. 1 is a schematic diagram of an electron beam melting machine (EBM machine) showing the internal arrangement of various components. The EBM machine 100 includes an electron beam generating section 105, an electron beam focusing section 110, and a deposition section 115. Generally, the electron beam generating section 105, the electron beam focusing section 110, and the deposition section 115 are assembled together such that an electron beam 120 from the electron beam generating section 105 propagates through the electron beam focusing section 110 to a reaction zone 125 in the deposition section 115.

[0015] The electron beam generating portion 105 is typically in the form of an electron beam column 130 that includes an electron beam source 135 (such as a filament) that, when powdered, generates the electron beam 120. Other subassemblies associated with the electron beam column include vacuum controls and a display system (not shown).

[0016] Electron beam focusing portion 110 contains structures for focusing, deflecting, and directing electron beam 120 , including an astigmatic lens 140 , a focusing lens 145 , and a deflection lens 150 .

[0017] The deposition section 115 includes one or more powder sources 155, such as reservoirs or hoppers, connected by conduits 160 to supply powder to a build tank 165. Within the build tank 165 is a translatable build platform 170 (typically translatable vertically as indicated by arrow V) and a powder layer 175. A starter plate 180 is placed within the powder layer 175, and as the build platform 170 translates and more powder is added to the powder layer 175 from the powder source 155, the starter plate 180 (and components accumulated on the starter plate 180) becomes embedded within the powder of the powder layer 175. A translatable arm 185, or similar device such as a rake or doctor blade (typically translatable horizontally as indicated by arrow H), supplies powder to the build tank and helps distribute and level each additional layer of powder during the subsequent additive manufacturing process. The reaction zone 125 is typically that portion of the powder layer 175 that interacts with the incident electron beam 120 to additively manufacture a current layer of components that are built up on a starting plate 180. The deposition portion 115 is typically contained within a vacuum chamber 190 or other structure to allow for atmospheric control in the reaction zone 125. A heat shield 195 is positioned between the path of the incident electron beam 120 and the powder source 155.

[0018] A controller (not shown) provides operational communication and control to the various components of the EBM machine to deposit material, such as metal, onto starting plate 180 on a layer-by-layer basis to produce an object of almost any shape or geometry using digital model data, e.g., a 3D model or a computer-aided design (CAD) model or another electronic data source, such as an additive manufacturing file (AMF) file or a stereolithography profile (STL) file.

[0019] An exemplary EBM machine is the Arcam EBM, marketed by GE Additive Company.

[0020] An EBM machine can be used to manufacture the components. In an exemplary embodiment, a manufacturing method uses an electron beam fusion additive manufacturing equipment, such as an EBM machine, to additively manufacture nuclear components. Figure 2 is a flow diagram describing basic steps in one embodiment of a method for manufacturing components by electron beam additive manufacturing using an EBM machine. The illustrated method S200 has various process steps including a build setup step S210, an initial heat treatment step S220, an initial powder layer establishment step S230, a pre-solidification heat treatment step S240, a solidification step S250, a post-solidification heat treatment step S260, and a post-build heat treatment step S290.

[0021] The illustrated process steps of method S200 also include a series of subsequent build-up steps of layers via additive manufacturing to produce the component. For example, for each layer, after the post-solidification heat treatment step S260 and before the post-build heat treatment step S290, the method S200 includes a step of indexing to the next layer S270 and a step of replenishing the powder layer S280, followed by the process steps of pre-solidification heat treatment step S240, solidification step S250, and post-solidification heat treatment step S260. The indexing step S270, replenishing step S280, pre-solidification heat treatment step S240, solidification step S250, and post-solidification heat treatment step S260 are repeated multiple times until the component is in its final form. The number of times these steps are repeated depends on the size of the component being manufactured and the thickness of each deposited layer, but exemplary numbers of times these steps are repeated include 2 to 10,000 times, with each deposited layer having a thickness ranging up to 80 microns, or 40 to 70 microns, or 45 to 55 microns, or about 50 microns (i.e., 50±1.5 microns). In a process with a subsequent build-up of layers, a post-build heat treatment step S290 occurs after completing the post-solidification heat treatment step S260 for the final layer.

[0022] The build setup step S210 prepares the EBM machine for operation. In an exemplary embodiment, the EBM machine was adapted to manufacture components having compositions disclosed herein using a starting plate 180 that substantially matches or matches the composition of the material to be deposited. For example, in a manufactured component having a composition consisting of molybdenum, the composition of the starting plate 180 also consists of molybdenum, and in a manufactured component having a composition consisting essentially of molybdenum, the composition of the starting plate 180 also consists essentially of molybdenum or a molybdenum-based alloy. Similarly, in a manufactured component having a composition consisting of a molybdenum-based alloy, the composition of the starting plate 180 also consists of a molybdenum-based alloy, and in a manufactured component having a composition consisting essentially of a molybdenum-based alloy, the composition of the starting plate 180 also consists essentially of a molybdenum-based alloy. In each of these cases, the composition of the material to be deposited and the purity levels of the composition of the starting plate may differ as long as these purity levels are within the ranges disclosed herein, e.g., 99.0% or greater. In an alternative embodiment, the composition of the starting plate is a molybdenum tungsten alloy or a molybdenum rhenium alloy, e.g., Mo 2 W or Mo 2 Without being bound by theory, the use of a starter plate with a composition aligned with the composition of the additive manufacturing powder was observed to minimize and / or avoid intermetallic layers that would occur if a molybdenum (or molybdenum-based) additive manufacturing powder were deposited onto a non-molybdenum (or non-molybdenum-based) starter plate, such as a stainless steel or titanium starter plate.

[0023] In an exemplary embodiment, the EBM machine is adapted to produce components having the compositions disclosed herein by increasing the thermal insulation of the start plate 180 such that the heat transfer from the start plate 180 to the surrounding environment is reduced compared to conventional EBM machines. Typically, EBM machines are designed such that the start plate sits on pins placed on the bottom surface of the build tank or on the inner surface of the translatable build platform, i.e., on the surface of the translatable build platform that faces the volume where the powder layer will be generated during operation. In contrast, in the exemplary embodiment disclosed herein, the start plate 180 sits directly on the layer of powder. Typically, the powder has the same composition as the powder used to produce the components. This layer of powder occupies the space between the start plate 180 and, for example, the inner surface of the translatable build platform 175. In an exemplary embodiment, this layer of powder has a thickness of 5 to 20 millimeters (mm), alternatively 7 to 15 mm, alternatively 8 to 12 mm, alternatively 10 mm. Also, typically, the powder of the powder layer has a thickness of less than or equal to 100 microns (d 90 ≦100μm) or d between 85 and 90 microns 90 Particle size, equal to or greater than 40 microns (d 10 ≥ 40 μm) or d between 45 and 50 microns 10 Particle size, and 70 microns (d 50 = 70 μm), or d between 65 and 75 microns or 68 and 72 microns 50 In some embodiments, the powders in the powder layer have the same composition and the same particle size, i.e., the same d 90 Particle size, d 10 Particle size and d 50 The particle size is the same as the powder in the feedstock used in additive manufacturing processes.

[0024] When starting plate 180 is seated on the powder bed, starting plate 180 is also positioned to be located within reaction zone 125. In an exemplary embodiment, starting plate 180 is positioned within the reaction zone such that the dimensions of the part to be produced are within the operating range of the electron beam.

[0025] The initial heat treatment step S220 prepares the starting plate for deposition of an initial layer by the EBM machine. For example, the initial heat treatment step S220 can include heating the starting plate to a particular temperature and maintaining that temperature for a period of time to sinter the powder underneath the starting plate so that if it accumulates on top of the powder layer, it forms a solid base underneath the starting plate.

[0026] In an exemplary embodiment, the initial heat treatment step S220 includes positioning the starting plate at a plate offset distance, which is an initial plate height adjustment to offset thermal expansion of the starting plate during starting plate heating. The plate offset distance depends on the material of the starting plate and the temperature to which the starting plate is heated.

[0027] In an exemplary embodiment, the initial heat treatment step S220 includes heating the starting plate to a first temperature. Heating to the first temperature allows the starting plate to thermally equilibrate for subsequent deposition of layers to form the component. The first temperature can range from 1030° C. to 1080° C., depending on the operating conditions of the electron beam and the expected temperature during deposition. The temperature of the starting plate 180 is monitored by a thermocouple in contact with the starting plate 180. In an exemplary embodiment, the electron beam 120 impinges on the starting plate 180 to heat the starting plate 180 to the first temperature.

[0028] In an exemplary embodiment, the initial heat treatment step S220 includes holding the starting plate at a first temperature to sinter a portion of the powder layer upon which the starting plate sits, i.e., a layer of powder occupying the space between starting plate 180 and, for example, an inner surface of translatable build platform 175. The hold time is sufficient to sinter the portion of the powder layer upon which the starting plate sits, such that the sintered powder provides a stable base for subsequent deposition of layers to form the component.

[0029] For example, the initial heat treatment step S220 may include rastering the electron beam 120 across the surface of the starting plate 180 until a thermocouple attached to the starting plate indicates a temperature between 1000° C. and 1300° C. for a period of 20 to 40 minutes, such as 1040° C. for a period of 30 minutes.

[0030] Table 1 below shows values ​​for parameters applicable to an exemplary embodiment of the initial heat treatment step S220 when using a starting plate 180 having a composition consisting of ≧99% purity molybdenum in the form of a disc having a diameter of 110 mm and a thickness of 8 to 12 mm, or 10 mm.

[0031] [Table 1]

[0032] The step S230 of establishing an initial powder layer takes powder supplied from the powder source 155 and establishes a base layer on the starting plate 180. The supplied powder covers at least a portion of the build surface of the starting plate 180 with a base layer of the first powder, and in the alternative, the supplied powder covers the entire build surface of the starting plate 180 with a base layer of the first powder. The build surface is the surface of the starting plate 180 on which deposition of layers to form a component occurs.

[0033] The base layer can be established by any suitable means. In an exemplary embodiment, powder from a powder source 155 is positioned near the powder layer, and a translatable arm 185, or a similar device such as a rake or doctor blade, is translated (typically horizontally) across the surface of the powder layer to distribute the supplied powder in a layer across the top surface of the powder layer, thus creating the base layer. This base layer has a thickness corresponding to the distance between the top layer of the existing powder layer and the lower surface of the translatable arm 185. In an exemplary embodiment, the base layer has a thickness in the range of 40 to 70 microns, or 45 to 55 microns, or about 50 microns (i.e., 50±1.5 microns).

[0034] In some embodiments, the powders in the base layer (and subsequent build layers) have the same composition and the same particle size, i.e., the same d 90 Particle size, d 10 Particle size and d 50 The particle size is the same as the powder in the powder layer below starting plate 180.

[0035] A pre-solidification heat treatment step S240 occurs at each layer and contributes to maintaining the build at a specific temperature and slightly sintering each new powder layer before solidification in order to minimize or prevent static charge build-up and particle shedding from the powder layer (a phenomenon known as "smoking"). In an exemplary embodiment, the pre-solidification heat treatment step S240 is a two-step heating process. In a first heating step, the powder layer (or the base layer of a subsequent build layer) is heated to a first pre-heat temperature to agglomerate the powder of the powder layer. In a second heating step, the base layer or a portion of the base layer is heated to a second pre-heat temperature (the second pre-heat temperature is higher than the first pre-heat temperature) to densify a portion of the agglomerated first powder. The area of ​​the densified portion of the agglomerated first powder has a boundary that surrounds the area where the current layer of the component will be formed. In some embodiments, the boundary of the area of ​​the densified portion of the agglomerated first powder can have a shape that corresponds to the shape of the current layer of the component to be formed. For example, the current layer of the component being formed has the shape of a circle, and then the boundary of the region of the densified portion of the agglomerated first powder also forms a circle having a larger diameter so as to be offset from the circumference of the circle of the current layer of the component being formed. By way of example, Figure 3 is a top view of a reaction zone, showing the current layer of the component being formed at 300, and diagrammatically the region of the densified and agglomerated first powder at 305 with boundary 310 and powder layer 315.

[0036] Table 2 below provides values ​​for parameters applicable to an exemplary embodiment of the heating step of the pre-consolidation heat treatment process when using a starting plate 180 having a composition consisting of ≧99% purity molybdenum in the form of a disk having a diameter of 110 mm and a thickness of 8 to 12 mm, or 10 mm, and a powder having a composition of 99.97 wt% Mo, 0.010 wt% O, 0.0030 wt% C, 0.015 wt% W, 0.0010 wt% Si, and 0.0005 wt% equal S, N, and Fe. The average grain size is 65.13±12.66 μm with a grain size distribution of D10, D50, and D9 equal to 49.61 μm, 63.89 μm, and 81.95 μm, respectively. The heating step of the pre-solidification heat treatment process can be done in two separate steps, a first step "Preheat I" and a second step "Preheat II". In Table 2, the parameters listed under Preheat I & II (Common) are common to both Preheat I and Preheat II steps, while the parameters listed under Preheat I and Preheat II are specific to the identified step, i.e., either the Preheat I step or the Preheat II step. With reference to FIG. 3, Preheat I is applicable to the area of ​​the powder layer 315 and Preheat II is applicable to the area of ​​the densified and agglomerated first powder 305.

[0037] [Table 2]

[0038] The above parameters in Table 2 can be adjusted by the user to provide heat input to the system to effect successful melting.

[0039] The solidification step S250 involves sintering a current layer of the component from the densified portion of the agglomerated first powder. For each layer, the solidification step is a self-contained electron beam melting operation that solidifies the new layer of powder onto the previously formed layer through electron beam melting. Of the various parameters associated with the solidification step, it has been determined that the melting parameters associated with energy density, energy input, and geometric accuracy have the greatest material impact on the process. Thus, an exemplary embodiment of the solidification step S250 includes parameters for focus offset, beam current, velocity function, current compensation, and tipping point function.

[0040] The beam focus offset (FO), measured in mA, controls the focus of the electron beam so that the focal point is at, on, or below the build surface and has a significant effect on the energy input. A focus offset value of 0 mA describes the current applied to the focus coils in the beam column that results in the most focused beam at the build surface. Exemplary values ​​for the focus offset parameter are 20 to 30. Other values ​​of the focus offset parameter may be used as long as such values ​​provide sufficient energy to create a melt pool and therefore a solid part.

[0041] The beam current, measured in milliamps (mA), provides the energy source for melting the metal powder. Exemplary values ​​for the beam current parameter are 2 mA to 30 mA. Generally, currents outside of this range will melt the part with too little energy or create a melt pool that is too large for the geometry being created.

[0042] The velocity function controls the relationship between beam velocity and beam current. It is designed to maintain a constant melt pool. Generally, the higher the value for the velocity function, the higher the beam velocity for a similar beam current. Exemplary values ​​for the velocity function parameter are 2 to 10, or 2 to 8, or 3 to 8. For molybdenum having a purity of 99.0% or greater, an exemplary velocity function is 5.

[0043] Current compensation is a mathematical model that modifies the hatch melt beam current as a function of the length being melted (line scan length). This function modifies the beam current to compensate for large and small areas within the same 2D slice of the part. Exemplary values ​​of the current compensation parameter are set such that the ratio of the reference scan line to beam current is as high as 1.35 and as low as 0.5. Generally, values ​​of the current compensation parameter below this range create issues with longer build times and the amount of energy being produced, while values ​​of the current compensation parameter above this range create issues with variable line spacing of adjacent melt pools.

[0044] The tipping point function is a mathematical model that changes the beam's travel speed when it changes direction and moves away from the edge of the part. The tipping point function is used to prevent overheating at the edge of the part, which can negatively affect the build quality. Exemplary values ​​of the tipping point function parameters are set with a pre-exponential factor of 0.5 to 1.3 and an exponential factor I of 0.0002 to 0.001. Generally, tipping point function values ​​that lead to too much energy going into the system lead to corners that are not geometrically correct or expand on premature layers, while tipping point function values ​​that lead to too little energy going into the system lead to corners not making contact with the underlying layer.

[0045] Table 3 below shows values ​​for parameters applicable to an exemplary embodiment of the consolidation step when using a starting plate 180 having a composition consisting of ≧99% purity molybdenum in the form of a disk having a diameter of 110 mm and a thickness of 8 to 12 mm, or 10 mm, and a powder having a composition of 99.97 wt% Mo, 0.010 wt% O, 0.0030 wt% C, 0.015 wt% W, 0.0010 wt% Si, and 0.0005 wt% equal S, N, and Fe. The average grain size is 65.13±12.66 μm with a grain size distribution of D10, D50, and D9 equal to 49.61 μm, 63.89 μm, and 81.95 μm, respectively.

[0046] [Table 3]

[0047] [Table 4]

[0048] The above parameters in Tables 3 and 4 can be adjusted by the user to provide heat input to the system to effect successful melting.

[0049] In addition, the raster direction during the solidification step can include an angular rotation designed to eliminate combinatorial stresses due to repeated thermal rises in localized regions of the component being fabricated. For example, the repeatability of electron beam rasterization patterns using 90 degree rotations can result in geometry-dependent expansion and build failures, especially in linear applications. Thus, in some embodiments, angular rotations to reduce repeatability can be used. For example, a non-90 degree angular rotation can be selected that repeats on a much less frequent basis. For example, angular rotation values ​​based on prime numbers repeat only once every 360 layers. In other embodiments, angular rotation values ​​based on integer multiples of prime numbers can be used. For example, a 66 degree angular rotation (a multiple of 6 times the prime number 11) repeats every 60 layers.

[0050] In another embodiment relating to thin-walled objects, a pattern can be used that deposits material to the thin-wall along the wall direction, i.e., in a direction that matches the orientation (within 10 degrees) along the length of the wall (as opposed to transversely to the wall direction, i.e., thickness direction).

[0051] Current compensation (i CCAdditional information regarding the tipping point function can be found in Sames, William (2015), “Additive Manufacturing of Inconel 718 using Electron Beam Melting: Processing, Post-Processing, & Mechanical Properties,” Doctoral dissertation, Texas A & M University. https: / / hdl.handle.net / 1969.1 / 155230, the entire contents of which are incorporated herein by reference. Additional information regarding the tipping point function can be found in Frederick, Curtis Lee, “Control Of Grain Structure In Selective-Electron Beam Melting Of Nickel-Based Superalloys.” PhD dissertation, University of Tennessee, 2018, https: / / trace.tennessee.edu / utk_graddiss / 4952, the entire contents of which are incorporated herein by reference.

[0052] The post-solidification heat treatment step S260 provides thermal management to maintain a specific temperature level during the entire build process, and more specifically, a consistent thermal environment during the deposition of successive layers of material. Due to the varying amount of melting in each layer, the post-solidification heat treatment step S260 may include a combination of periods of heating, periods of cooling, or one or more periods of heating and one or more periods of cooling, such that an overall thermal balance is maintained. The post-solidification heat treatment step S260 returns the powder layer to the temperature achieved during the pre-solidification step S240. For example, the post-solidification heat treatment step S260 includes heating both the agglomerated powder layer and the fully solidified regions utilizing the same parameters utilized by the second step Preheat II in the pre-solidification step S240, such that the temperature of the powder layer achieved as a result of performing the pre-solidification step S240 is achieved in the result of the post-solidification step S260.

[0053] The post-heat step occurs after the solidification step. The post-heat step behaves similarly to the pre-heat stage that occurs after melting, except that the same area of ​​the powder layer is heated with the same parameters used in pre-heat II. The post-heat time is determined based on the heat already input from the previous pre-heat and solidification steps.

[0054] After the post-solidification heat treatment step S260, the method S200 either proceeds to continue building up the component through the process of depositing subsequent layers of material, or proceeds to post-build steps that include a cooling step.

[0055] When proceeding to continue to grow the component, method S200 includes processes to deposit one or more subsequent layers of material. For example, after the post-solidification heat treatment step S260, method S200 includes an indexing step S270 and a refilling step S280, followed by a pre-solidification heat treatment step S240, a solidification step S250, and a post-solidification heat treatment step S260. The indexing step S270, the refilling step S280, the pre-solidification heat treatment step S240, the solidification step S250, and the post-solidification heat treatment step S260 can be repeated multiple times until the component is in its final form.

[0056] In an indexing step S270, the position of the starting plate 180 is moved a distance corresponding to the thickness of the subsequent layer. In an exemplary indexing step, the position of the starting plate 180 is moved a distance of 40 to 70 microns, alternatively 45 to 55 microns, or approximately 50 microns (i.e., 50±1.5 microns). Then, in a refill step S280, the current layer of the component is covered with a layer of feedstock powder, such as by the action of a translatable arm 185, or a similar device such as a rake or doctor blade (typically translatable horizontally as indicated by arrow H), which supplies powder to the build tank and helps distribute and level the coating layer.

[0057] Upon completion of the build of the component in the EBM machine additive manufacturing process, the method S200 proceeds to a post-build heat treatment step S290. Either prior to or as an initial part of the post-build heat treatment step S290, the heat input to the component is removed. This can be accomplished, for example, by shutting off the electron beam 120. With the heat input removed, the post-build heat treatment step S290 proceeds to a cooling step. In one embodiment, the cooling step includes maintaining the vacuum atmosphere in the vacuum chamber 190 at atmospheric pressure for 20±2 minutes, followed by backfilling the vacuum chamber 190 with an inert gas, and then cooling the open-air, environment to ambient temperature. In another embodiment, the cooling step includes cooling the component under inert gas to a temperature of <100° C., followed by opening the chamber and allowing the open-air, environment to cool to ambient temperature. An exemplary inert gas suitable for use in either embodiment is helium gas. In both embodiments, the details of the cooling step are designed to cool the completed component slowly and evenly to reduce the effects of thermal cracking.

[0058] All values ​​of parameters disclosed in the above discussion and tables are based on LaB 6 It is based on an Arcam EBM Spectra H with a quartz cathode.

[0059] One or more or all of the above parameters may be pre-programmed into a build package that can be used as instructions for operating the electron beam fused deposition modeling equipment. Alternatively, one or more or all of the above parameters may be edited directly through the user interface of the electron beam fused deposition modeling equipment, such as through a "theme editor" feature or equivalent.

[0060] Further, the geometric details of the component can be inputted into the EBM machine in an input step. An exemplary input step includes inputting the component geometry into a controller of an electron beam fusion deposition modeling machine. The component geometry can be on a layer-by-layer basis or on a whole component basis. In an exemplary embodiment, the component geometry is embodied in a computer-aided design (CAD) model or an additive manufacturing file (AMF) file or a stereolithography profile (STL) file.

[0061] 4A and 4B are images of exemplary molybdenum structures produced by electron beam additive manufacturing. The molybdenum structures are rectangular prisms and are shown seated on a pure molybdenum plate. The molybdenum structures shown are built up layer-by-layer in the Z-axis direction (i.e., perpendicular to the surface of the starting plate) using the methods disclosed herein. FIG. 4B is a magnified image of four samples from FIG. 4A, the four samples being labeled 4, 5, 7, and 8. Sample 4 is also shown in FIG. 4A.

[0062] Figure 5 is a near infrared (NIR) image of the exemplary molybdenum structure shown in Figure 4A taken during an electron beam additive manufacturing process. This NIR image shows that non-destructive evaluation can occur during the EBM machine additive manufacturing process to monitor for structural defects, such as voids in the component that are building up. Such in-situ non-destructive evaluation can be used for quality control purposes.

[0063] 6A and 6B are metallographic images of a first cross section (XY plane) (FIG. 6A) and a second cross section (YZ plane) (FIG. 6B) of an exemplary molybdenum structure produced by electron beam additive manufacturing. The exemplary molybdenum structure corresponds to Sample 4 of FIGS. 4A and 4B. The metallographic images of FIGS. 6A and 6B are at 100X magnification. As can be seen from FIGS. 6A and 6B, the metallographic cross section is crack-free. FIG. 6B is crack-free, while FIG. 6A includes a single crack (seen along the right edge of FIG. 6A) having a length of 1.5 mm, meaning that the total crack length in FIG. 6A is 1.5 mm. As used herein, crack-free means that the metallographic cross section of the component viewed at 100X magnification includes internal cracks having a total crack length of less than 4 mm, or less than 3 mm, or less than 2 mm (where total crack length = sum of lengths of all visible cracks). In some embodiments, no cracks means that a metallographic cross-section of the component viewed at 100X magnification does not contain internal cracks. In this context, the cracks relevant to this evaluation may be one or more of metallurgical cracks, i.e., cracking at grain boundaries, and incomplete fusion defects, i.e., defects caused by localized insufficient energy input that leads to the powder not being completely melted.

[0064] Also, as can be seen in Figures 6A and 6B, the metallographic cross section is void-free and crack-free. Both Figures 6A and 6B are pore-free. As used herein, void-free means that (i) the metallographic cross section of the component viewed at 100X magnification does not contain any visible pores, and (ii) the sample has a density within 0.10 percent of the theoretical density for the material when density measurements are made using helium pycnometry. For example, molybdenum, which has a theoretical density of 99.84% and a measured density of 99.75% or greater, is within 0.10 percent of the theoretical density.

[0065] Material characterization tests were performed on Sample 4. The composition of Sample 4 is listed in Table 5.

[0066] [Table 5]

[0067] In some embodiments, the component has a composition consisting of molybdenum or a molybdenum-based alloy with a purity level (of molybdenum or molybdenum-based alloy) of 99.0% or greater, or 99.3% or greater, or 99.5% or greater, such as 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, 99.91%, 99.92%, 99.93%, 99.94%, 99.95%, 99.96%, 99.97%, or 99.98% purity. In some embodiments, the component has a composition consisting essentially of molybdenum or a molybdenum-based alloy. In embodiments where the composition consists essentially of molybdenum or a molybdenum-based alloy having a purity level (of molybdenum or molybdenum-based alloy) of 99.0% or greater, or 99.3% or greater, or 99.5% or greater, such as 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, 99.91%, 99.92%, 99.93%, 99.94%, 99.95%, 99.96%, 99.97%, or 99.98% purity, other materials (including other metals or metal alloys) may be present in the component, so long as the component has a composition consisting essentially of molybdenum or a molybdenum-based alloy. In some embodiments, the other materials are limited only to the purity level and are not intentionally added to the composition.

[0068] In some embodiments of components manufactured by the disclosed EBM machine additive manufacturing process having a composition consisting or consisting essentially of molybdenum or a molybdenum-based alloy, the component is full density. As used herein, full density has a density of 99.75% or greater, such as 99.80% or 99.85% or 99.00% or 99.95% or 99.98% or 99.99% or 100% density of metal powder, as calculated based on the volume determined by pycnometry using a gas pycnometer and He gas, and according to the ASTM B923-21 Standard Test Method for Metal Powder Skeletal Density by Helium or Nitrogen Pycnometry.

[0069] For example, the density of sample 4 was 10.2045 g / cm3 by gas pycnometer and He gas pycnometer measurement. 3 (0.0071g / cm 3 The pycnometer was determined to have a reading of 0.0015 cm for the volume for three successive cycles. 3 Repeated cycles were performed on the samples until the mass was within a set standard deviation of 10.2045 g / cm. The weight of the sample was determined by use of a graduated analytical balance with a measurement error of 0.0001 g and used with the volume determined by the pycnometer to determine the density. 3 The determined density of sample 4 is 10.22 g / cm for pure molybdenum. 3 Based on the theoretical density, sample 4 has a density of 99.84%.

[0070] Although particular embodiments have been mentioned, it will be apparent that other embodiments and modifications may be devised by those skilled in the art without departing from the spirit and scope thereof, and it is intended that the appended claims be construed to include all such embodiments and equivalent modifications. [Explanation of symbols]

[0071] 100 EBM machine 105 Electron beam generating section 110 Electron beam focus unit 115 Deposition part 120 Electron Beam 125 Reaction Zone 130 Electron Beam Column 135 Electron Beam Source 140 Astigmatic Lens 145 Focus Lens 150 deflector lens 155 Powder Source 160 Conduit 165 Build Tank 170 Build Platform 175 Powder layer 180 Starting Plate 185 Arm 190 Vacuum Chamber 195 Heat Shield

Claims

1. A method for manufacturing a component by electron beam melting and deposition manufacturing, comprising: A build setup step including seating a starting plate on a powder layer within a reaction zone of a vacuum chamber of an electron beam melting and deposition manufacturing machine, wherein the starting plate has a composition consisting of molybdenum having a purity of 99.0% or more, and the powder layer includes a first powder having a composition consisting of molybdenum having a purity of 99.0% or more; An initial heat treatment step of positioning the starting plate at a plate offset distance based on the thermal expansion of the starting plate during the initial heat treatment step, heating the starting plate to a first temperature sufficient to sinter the powder layer and being 1040 °C or higher and 1350 °C or lower, holding the starting plate at the first temperature, and sintering a part of the powder layer on which the starting plate is seated; Covering at least a part of the build surface of the starting plate with a base layer of the first powder; A pre-solidification step including a first heating step of heating the base layer to a first preheating temperature and a second heating step of heating the base layer to a second preheating temperature, wherein the second preheating temperature is higher than the first preheating temperature, the first preheating temperature agglomerates the first powder of the base layer, and the second preheating temperature densifies a part of the agglomerated first powder; A solidification step including sintering a current layer of the component from the densified part of the agglomerated first powder, wherein the rasterization pattern used for sintering during the solidification step is non-90 degrees and includes angular rotation based on a prime number or a multiple of an integer of a prime number; A post-build step including a cooling step.

2. After the solidification step and before the post-build step, The method according to claim 1, further comprising a post-solidification step including returning the powder layer to the second preheating temperature.

3. After the post-solidification step and before the post-build step, An indexing step including moving the position of the starting plate by a distance corresponding to the thickness of a subsequent layer; A replenishment step in which the current layer of the component is covered with a layer of the first powder; The method according to claim 2, further comprising performing the pre-solidification step and the solidification step.

4. The method according to claim 3, wherein the post-curing step, the indexing step, the replenishment step, the pre-curing step, and the curing step are repeated a plurality of times until the component reaches its final form.

5. The method according to any one of claims 1 to 4, wherein the plate offset distance is 0.1 mm or more and 0.3 mm or less.

6. The method according to any one of claims 1 to 4, wherein the region of the densified portion of the first powder formed into a mass has a boundary surrounding the region where the layer of the component is formed.

7. The method according to any one of claims 1 to 4, wherein the component has a composition consisting of molybdenum having a purity equal to or greater than 99.0% and a density equal to or greater than 99.75%.

8. The method according to claim 7, wherein the component is crack-free.

9. The method according to claim 7, wherein the component has no gaps.

10. The method according to claim 7, wherein the component is crack-free and has no gaps.

11. The plate offset distance is 0.1 mm or more and 0.3 mm or less, the region of the densified portion of the first powder formed into a mass has a boundary surrounding the region where the layer of the component is formed, and the component has a composition consisting of molybdenum having a purity equal to or greater than 99.0% and a density equal to or greater than 99.75%. The method according to any one of claims 1 to 4.

12. The cooling step includes removing the heat input to the component, and maintaining the vacuum atmosphere in the vacuum chamber at atmospheric pressure for 20 ± 2 minutes, followed by backfilling the vacuum chamber with an inert gas, or (b) cooling the component to 100°C under an inert gas. The method according to any one of claims 1 to 4.

13. The method according to claim 12, wherein the inert gas is helium.

14. The method according to any one of claims 1 to 4, further comprising a geometry input step including inputting the geometry of the component into a controller of the electron beam melting deposition manufacturing machine.

15. The method according to claim 14, wherein the geometry of the component is a layer-by-base geometry.

16. The method according to claim 15, wherein the geometry of the component is embodied in a computer-aided design (CAD) model or a stereolithography (STL) file or an additive manufacturing file (AMF) file.

17. The method according to any one of claims 1 to 4, wherein the base layer has a thickness of 40 to 70 microns.

18. The method according to claim 17, wherein the thickness of the base layer is 45 to 55 microns.

19. The first heating step of the pre-curing step includes a first plurality of parameters including a current of 20 mA to 40 mA, a maximum number of sweeps of 300, a number of sweeps at a maximum current of 50, a beam speed of 20,000 mm / s, a focus offset of 375 mA, and a line offset of 1 mm. The method according to any one of claims 1 to 4, wherein the second heating step of the pre-curing step includes a second plurality of parameters including a current of 40 mA to 45 mA, a maximum number of sweeps of 30, a number of sweeps at a maximum current of 1, a beam speed of 16,100 mm / s, a focus offset of 375 mA, and a line offset of 1 mm.

20. The curing step includes a third plurality of parameters including a focus offset, a beam current, a velocity function, a current compensation, and a transition point function. The focus offset is from 5 mA to 30 mA. The beam current is from 2 mA to 30 mA. Due to the value of the current compensation, the ratio of the reference scan line to the beam current is from 0.5 to 1.

35. The transition point function is as follows: 【Number 1】 is defined by where the pre-exponential factor (PEF) is from 0.5 to 1.3 and the exponential factor 1 (EF 1) is from 0.0002 to 0.

001. The method according to claim 19.

21. The method according to claim 19, further comprising a geometry input step including inputting the geometry of the component into a controller of the electron beam melting additive manufacturing machine, wherein the geometry of the component is a layer-by-base geometry.

22. The plate offset distance is 0.1 mm or more and 0.3 mm or less. The region of the densified portion of the first powder formed into the blocks has a boundary surrounding the region where the layer of the component is formed. The method according to claim 19, wherein the component has a composition consisting of molybdenum having a purity equal to or greater than 99.0% and a density equal to or greater than 99.75%.

23. The method according to claim 19, wherein the component is a nuclear component.

24. A component for a nuclear reactor manufactured by the method according to claim 23.

25. The method according to any one of claims 1 to 4, wherein the component is a nuclear component.

26. A component for a nuclear reactor manufactured by the method according to any one of claims 1 to 4.

Images