Method for forming a cladding layer with an integral channel

Abstract

Procedure, comprehensive: Immersion of a preform (10) into a layer (12) of powdered material (14), wherein the preform defines a desired shape of a cavity (60, 62, 64, 78) to be formed in a layer (42) of superalloy material; Melting the powdered material around the preform without melting the preform itself; and Cooling and resolidifying the molten material around the preform to form the layer of material, the preform defining the shape of the cavity within it. characterized by that the material (14) is a superalloy material, that the preform (10) is a ceramic preform, wherein, during melting by laser heating to facilitate wetting of the preform, at least one of the following steps is performed: slowing down a movement speed of the laser in the area of ​​the preform, changing an angle of the laser in the area of ​​the preform, adjusting convective effects in the area of ​​the preform, adjusting surface tension effects in the area of ​​the preform, rotating the preform and moving the preform.

Description

[0001] The invention relates generally to additive manufacturing and in particular to the formation of a material layer with an internal cavity or an internal channel with fine detail and, in one embodiment, to the formation of a superalloy cladding layer containing a precision-detailed cooling channel, using a cladding operation with a high deposition rate.

[0002] Additive manufacturing is generally considered the process of building three-dimensional components through multi-layer processing, with each layer representing a section of the component. The three-dimensional component can be manufactured using energy sources with sufficiently high power to melt a powdered material or alloy used in the component. For example, high-power laser beams are commonly used in such a way that the laser sinters or melts the powdered metal or alloy layer by layer. These processes include selective laser sintering (SLS), selective laser melting (SLM), direct metal laser sintering (DMLS), laser engineered net shape (LENS), and others. These processes build the component by processing many tiny layers.However, these processes have disadvantages and limitations. For example, some of the processes are excessively slow and unaffordable if many parts are required or if a part is relatively large.

[0003] High-deposition laser cladding, such as that described in US patent publication number US 2013 / 0140278A1 by Bruck et al. and incorporated here in its entirety by reference, solves the velocity problem. However, many gas turbine engine components used to guide hot gases require cooling channels located near the surface. These cooling channels contain fine detail that has not yet been achieved using the processes mentioned above. Consequently, there is still room for improvement in the technology.

[0004] A generic process is known from DE 100 33 794 C1. Further processes are described in US 2011 / 0 189 440 A1 and US 6 921 014 B2.

[0005] The purpose of the invention is to achieve an improved laser melting process.

[0006] The problem is solved in a generic method by the features of the characterizing part of claim 1. Preferred embodiments are specified in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The invention is explained in the following description with reference to the drawings, which show the following: Fig. Figure 1 schematically illustrates the positioning of a preform in a layer of powdered superalloy material. Fig. Figure 2 schematically illustrates the melting of the superalloy material around the preform without melting the preform itself, and the cooling and resolidification of the superalloy material. Fig. Figure 3 is a close-up view of a deposition process. Fig. Figure 4 schematically shows a layer with over the in Fig. The cooling passages shown in 1-3 are part of the process. Fig. Figure 5 schematically shows a component with the repetition of the in Fig. Cooling passages formed in the process shown in 1-3. Fig. Figure 6 schematically shows a preform with structural surface detail. DETAILED DESCRIPTION OF THE INVENTION

[0008] The inventors propose using a finely detailed preform that does not melt during a high-deposition-rate cladding process to create finely detailed channels (also known as cavities) within a superalloy cladding layer. The channels can be used for cooling, diagnostic, or other purposes, depending on the application. An embodiment of cooling channels is chosen here for discussion. However, the process is applicable to other cavities, such as branch channels, to accommodate instrumentation like a thermocouple. After the cladding process is complete and the cladding layer is formed, the preform can be removed to reveal the channel. Alternatively, the preform can remain in the cladding layer, defining the channel itself.The inventors recognized that a ceramic preform immersed in an alloy melt bath might not be completely wetted, particularly if the preform's surface contains fine structural detail. Accordingly, the preform of the present invention can be coated with a metal or metal alloy compatible with the superalloy material. This metal coating can improve the wetting of the molten superalloy material at the preform's geometry, thereby preserving the fine detail of the preform surface in the subsequently cooled cladding layer.

[0009] Fig. Figure 1 schematically illustrates the positioning of a preform 10 in a layer 12 of powdered superalloy material 14, arranged on a substrate 16 (or process bed). A layer 18 of powdered flux 20 can be placed on top of the layer 12 of powdered superalloy material 14. Alternatively, the powdered superalloy material 14 and the powdered flux 20 can be mixed together. In another alternative embodiment, an inert protective gas or a vacuum can be used instead of (or in addition to) the powdered flux 20 to avoid atmospheric reactions during processing. The preform 10 can be made of any material that does not melt during the cladding operation. The preform 10 can be solid (e.g., a thread) or can have a shape that defines a passage through it (e.g., a tube or foam with associated porosity).The size and shape of the preform correspond to the geometric detail of the desired openings or cavities in the final part. Examples of preform materials include ceramics such as aluminum oxide and zirconium oxide. Aluminum oxide rods (filaments) with a diameter of only 0.28 mm are currently available. Zirconium oxide rods (filaments) with a diameter of only 1.6 mm are currently available, for example, from Ortech Advanced Ceramics in Sacramento, CA, USA. Both aluminum oxide and mullite (3Al₂O₃ 2SiO₂) are available in tube form, for example, from Coorstek of Golden Co., USA.

[0010] Optionally, an outer surface 30 of the preform 10 can be coated with a coating 32 (e.g., a metal coating) to facilitate wetting during the laser cladding operation. Suitable materials for the preform 10 include aluminum oxide, beryllium oxide, sapphire, zirconium oxide, silicon oxide, magnesium oxide, boron nitride, aluminum nitride, silicon nitride, silicon carbide, aluminum silicates (including mullite), magnesium silicates, and any other suitable ceramic. Suitable coating materials include molybdenum-manganese, tungsten-manganese, moly-tungsten-manganese, titanium, hafnium, zirconium, chromium, and niobium. Any combination of the above preform materials and coating materials can be used.

[0011] In one embodiment, an aluminum oxide, beryllium oxide, or sapphire preform 10 can be coated with any molybdenum-manganese, tungsten-manganese, or moly-tungsten-manganese alloy. The preform 10 can be coated using one of several known processes, including brushing, screen printing, spraying, dipping, plating, sputtering, and needle application. Typically, the coating 32 can have a thickness of twenty-five micrometers, with a tolerance of ten micrometers. If the coating 32 is a plating, it can have a thickness of two to ten micrometers. Accordingly, in some cases, a plating can be applied directly to the preform 10 without an intermediate coating to achieve wetting. Optionally, a second coating 34 can be applied to a surface 36 of the coating 32 to further facilitate wetting.The second coating 34 can comprise a metal or alloy compatible with the powdered superalloy material 14, which is applied during a plating process, in which case the second coating 34 is a plating. For example, nickel can be used for the second coating 34 for a nickel-based powdered superalloy material. Again, the plating, and thus the second coating 34, can have a thickness of two to ten micrometers. An optional final step in the metallization of the preform 10 can include heat treatment. In one embodiment, an aluminum oxide preform 10 is coated with molybdenum-manganese plated with nickel.

[0012] In an alternative embodiment, a zirconium oxide preform 10 can be coated with titanium (commercially available from Forschungszentrum Jülich in Jülich, Germany) via physical vapor deposition. Other materials suitable for the deposition of zirconium oxide (via physical vapor deposition) include hafnium, zirconium, chromium, and niobium.

[0013] The coating 32 and the optional second coating 34 improve the wetting of the molten superalloy material onto the preform during the cladding operation. The coating 32 and the optional second coating 34 may or may not be consumed during the cladding operation. If it is consumed, the molten superalloy material will conform directly to the outer surface 30 of the preform 10. If it is not consumed, the molten superalloy material will conform to the outer surface 36 of the coating 32 if only the coating 32 is present, or to an outer surface 38 of the second coating 34 if the second coating 34 is present.Since a shape of the outer surface 30 of the preform 10 defines a shape of the surface 36 of the coating 32 as well as a shape of the outer surface 38 of the second coating 34, the molten superalloy material still conforms to the shape of the outer surface 30 of the preform 10. Solidification of the molten superalloy material around the details preserves the details in the cladding layer.

[0014] If the coating 32 and / or the second coating 34 are consumed during the cladding operation, it will not have a detrimental effect on the cladding layer because the elements present in the coating 32 and in the second coating 34 are preferably already present in the relevant alloys (e.g. nickel-based superalloys) and the added amount of material would be so small that it would not have a significant effect on the cladding layer composition or mechanical or physical properties.

[0015] Fig. Figure 2 schematically illustrates the melting of the powdered superalloy material 14 around the preform 10 without melting the preform 10 itself. The melting can be accomplished in any manner known to those skilled in the art. In one embodiment, a laser beam 40 selectively heats the powdered superalloy material 14 to create a melt pool of molten superalloy material. The molten superalloy material cools and solidifies to form a cladding layer 42 covered by a layer of slag 44. The preforms 10 remain intact within the cladding layer 42.

[0016] Fig. Figure 3 is a close-up of the melting process. As the laser beam 40 moves in a direction of motion 50, it melts the powdered superalloy material 14 and the flux material 20 to form the melt pool 52 covered by the slag 44. Upon reaching a preform 10, the moving melt pool 52 surrounds the preform 10, retaining every detail present in the preform 10, while the molten superalloy material solidifies around the preform. If the coating 32 remains after the preform 10 is removed, the cooling channel is defined by an internal surface 54 of the coating 32. If the coating 32 is consumed, the cooling channel is defined by an internal surface of the cladding layer 42 after the preform 10 is removed.

[0017] Conventional laser heating generally positions the laser beam 40 above the preform 10 during the heating process. Consequently, powdered superalloy material 14 in a shaded area 56 (e.g., shaded from direct laser impact) beneath the preform 10 may not be directly heated by the laser beam 40. To ensure that the powdered superalloy material 14 in the shaded area 56 melts and that the molten superalloy material reaches a bottom surface 58 of the preform 10, the laser beam 40 can slow its velocity near the preform 10. Increasing the heat transfer into the melt pool 52 at the preform 10 can enhance the conductive heat transfer to the powdered superalloy material 14 in the shaded area 56. Preform materials with high thermal conductivity, such as aluminum oxide, can further enhance the heating to the shaded area 56.This can promote greater heating and melting of the powdered superalloy material 14 in the shaded area 56. Subsequent mixing of such material with the remainder of the melt pool 52 results from a temperature gradient (Rayleigh-Bénard convection) as well as a surface tension gradient (Marangoni convection). Movement of the melt, which promotes wetting by such convective effects, can be supplemented by mechanical movement. For example, the preform itself could be vibrated or rotated to increase wetting. The laser beam 40 can also be angled differently as it passes over the preform 10 (e.g.,(in the preform) in such a way that the laser beam 40 partially or completely reaches the shadowed area 56, which the laser beam 54 would not reach if the orientation of the laser beam 40 used in the remainder of the laser processing were not altered. The improved wetting provided by the coating 32 and / or the second coating 34 will also facilitate the movement of the molten material along the underside surface of the preform 10. Individual or combined effects of slowed laser movement, an angled laser, a conductive preform, convective effects, surface tension effects, and mechanical movements can improve the molten superalloy material completely surrounding the preform 10 and conforming to the shape of the outer surface 30 of the preform 10.The individual or combined effects can be used when the laser beam 40 is located at the preform 10 (i.e. close enough to the preform 10 to have an effect on the shadowed area 56).

[0018] Fig. Figure 4 shows the cladding layer 42 with the slag layer 44 removed. This cladding layer 42 can be a repair to a component or a layer of a new component. Three cooling channels 60, 62, and 64 are visible. In one embodiment, the preform 10 was removed, and a first cooling channel 60 is defined by the inner surface 66 of the cladding layer 42. This can occur if there was no coating 32 or second coating 34 on the preform 10 or if it was consumed during the cladding operation. In this case, the molten material conformed to the outer surface 30 of the preform 10. The preform 10 can be removed by mechanical, chemical, or other means known to those skilled in the art. For example, the preform can be broken and shattered using ultrasonic energy and reduced to powder, which is then rinsed away using a fluid such as compressed air or a cleaning agent.Preforms made of foam or pressed powder structure can be relatively fragile to facilitate removal. If the preform 10 has a hollow shape, such as a tube, foam, etc., it can be broken, shattered, and removed by thermal shock. For example, liquid nitrogen can be forced through the preform 10, causing it to break, allowing for removal then or afterward. Alternatively or additionally, if the preform 10 is hollow, it can be broken, shattered, and removed by mechanical shock (e.g., ultrasound).

[0019] In one embodiment, the preform 10 was removed and a second cooling channel 62 is defined by the inner surface 54 of the coating 32. This can occur if the preform 10 has the coating 32 and optionally the second coating 34, and the coating 32 is removed during the cladding operation. Fig. 3 is not consumed (whether the second coating 34 is consumed or not).

[0020] In one embodiment, the preform 10 remains in place, and a third cooling channel 64 is defined by an inner surface 68 of the preform 10, which is, for example, a hollow tube or a foam. If the preform 10 is a foam that remains in place, the associated porosity of the foam can enhance the cooling effect of the cooling channel 64. A hollow preform 10 may also be coated and optionally clad.

[0021] Fig. Figure 5 schematically shows a component 70 with, by repeating the in Fig. The cooling channels produced during an additive manufacturing process are shown in Figures 1-3 of the cladding process. Each iteration of the process forms a separate cladding layer 42. The component 70 can contain one or more cladding layers 42, or it can consist entirely of cladding layers 42. The component can be machined between the formation of the cladding layers 42 and / or after all cladding layers 42 have been applied. In the illustrated embodiment, several cladding layers 42 contain individual cooling channels, but each cladding layer 42 does not necessarily need to have its own cooling channel.

[0022] Each cladding layer 42 can have a specific type or types of cooling channels, and these cooling channels can have any orientation, size, and cross-sectional shape. A first cladding layer 72 contains cooling channels 60 defined by the inner surface 66 of the cladding layer 42 and oriented in one direction. A second cladding layer 74 contains cooling channels 64 defined by an inner surface 68 of the preform 10 and oriented in a different direction. A third cladding layer 76 contains a cooling channel 78 with a different polygonal shape oriented in yet another unique direction. A fourth cladding layer 80 has no cooling channel. Embodiments within the scope of this disclosure can connect cooling channels from one cladding layer 42 to another cladding layer 42.The connection can be provided by subsequent machining, or connecting passages can be formed as part of the cladding operation by using a preform including a vertically extending leg. In this way, cooling passages could extend laterally (within a given cladding layer 42) as well as vertically from one cladding layer 42 to another. Although connected channels for cooling have been described, channels for other purposes could be included. For example, a channel terminating at an important diagnostic location could be provided by a tubular preform with a matching end. After partial completion, instruments such as a thermocouple can be inserted through the tubular preform or into the channel formed by the preform.

[0023] Fig.Figure 6 schematically shows a preform 10 with details in the outer surface 30 that are reproduced in the cooling channels subsequently formed. Examples of such details include a raised or recessed rib 80 (as known from Kakac et al., "Heat Transfer Enhancement of Heat Exchangers"), raised or recessed release strips 82, raised or recessed angles 84, and raised or recessed pits 86, or any other feature known to those skilled in the art, arranged on the inner or outer surface of the preform. These details can, for example, increase the heat transfer to a cooling fluid in the cooling channel and / or regulate the flow rate of the cooling fluid flowing through the cooling channel.

[0024] Geometries other than wires / threads and tubes can be used for preform 10. Flat plates, for example, can be used in semiconductor applications. Single and double curved plates can be used, for example, in body armor applications. Valves with precisely dimensioned holes can be formed, for example, for components that measure blood. Cups and specialized contours can be used, for example, in orthopedic implants. These non-limiting examples represent only a few of the possible applications for the process disclosed herein.

[0025] From the above, it is evident that the inventors have developed a new and innovative method for forming a material layer containing an internal cavity with a highly detailed internal surface geometry, using a high-speed cladding process with a preform at a relatively high temperature. This process has achieved a level of detail previously unattainable with such a method and can be used in an additive manufacturing process to produce parts faster than ever before. This therefore represents a significant technological advancement.

[0026] Although various embodiments of the present invention have been shown and described herein, it is obvious that such embodiments are presented only as examples. Numerous variations, modifications, and substitutions can be made without departing from the present invention. Accordingly, the invention is to be limited only by the concept and scope of protection of the appended claims.

Claims

[1] Procedure, encompassing: Immersion of a preform (10) into a layer (12) of powdered material (14), wherein the preform defines a desired shape of a cavity (60, 62, 64, 78) to be formed in a layer (42) of superalloy material; Melting the powdered material around the preform without melting the preform itself; and Cooling and resolidifying the molten material around the preform to form the layer of material, the preform defining the shape of the cavity within it. characterized by , that the material (14) is a superalloy material, that the preform (10) is a ceramic preform, wherein, during melting by laser heating to facilitate wetting of the preform, at least one of the following steps is performed: slowing down a movement speed of the laser in the area of ​​the preform, changing an angle of the laser in the area of ​​the preform, adjusting convective effects in the area of ​​the preform, adjusting surface tension effects in the area of ​​the preform, rotating the preform and moving the preform. [2] Method according to claim 1, wherein the preform comprises a hollow ceramic tube. [3] Method according to claim 2, further comprising removing the hollow ceramic tube via a mechanical or thermal shock process. [4] Method according to any one of claims 1 to 3, further comprising coating an outer surface of the ceramic preform prior to the immersion and melting step to facilitate wetting of the preform by the molten superalloy material. [5] Method according to claim 4, wherein the outer surface of the preform is coated with at least one material from the group consisting of molybdenum-manganese, titanium, tungsten-manganese, moly-tungsten-manganese, hafnium, chromium, zirconium and niobium. [6] The method of claim 5, further comprising the plating of the coating prior to the immersion and melting step, wherein both the coating and the plating facilitate the wetting of the preform by the molten superalloy material. [7] Method according to any one of claims 1 to 6, wherein the preform comprises a raised or recessed surface feature (80, 82, 84, 86) on an outer or inner surface, wherein the method further comprises coating any raised or recessed surface feature on the outer surface, wherein a coating material is effective in facilitating the wetting of the surface feature with the molten superalloy material during the melting step. [8] Component comprising a plurality of layers formed during an additive manufacturing process, wherein one layer of the plurality is formed by the method according to any one of claims 1 to 7.

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