Patent Application
20190247921
The present disclosure generally relates to methods of manufacturing components using metal alloys. More particularly, the present disclosure relates to additively manufactured turbine components using binder jet printing with nickel-chromium-tungsten-molybdenum alloys.
Gas turbine engine components operating at high temperatures rely on applied protective coatings such as aluminides as a first line of defense against oxidation. However, where the protective coating is worn off, eroded or otherwise breeched, it is highly desirable that the exposed parent metal itself possess sufficient oxidation resistance for durability. Nickel-Chromium-Tungsten-Molybdenum (Ni—Cr—W—Mo) alloys such as Haynes 230® provide excellent oxidation resistance at high temperatures and are used in engine applications with high temperature environments such as combustors.
Accordingly, it is desirable to provide improved methods for manufacturing components from Ni—Cr—W—Mo alloys. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings.
According to various embodiments, exemplary methods for manufacturing an article include providing a three-dimensional computer model of the article and providing a metal alloy in powdered form. The metal alloy is a nickel-chromium-tungsten-molybdenum alloy. The powdered form includes a grain size range of about 5 to about 22 microns and a d50 grain size average of about 10 to about 13 microns. The exemplary methods further include, at a binder jet printing apparatus, supplying the metal alloy and loading the three-dimensional model, and, using the binder jet printing apparatus, manufacturing the article in accordance with the loaded three-dimensional model in a layer-by-layer manner with the supplied metal alloy. A liquid binder is applied at each layer, and each layer has a thickness of about 10 to about 150 microns. Still further, the exemplary methods include performing one or more post-print processes selected from the group of: curing, powder removal, de-binding, sintering, hot isostatic pressing (HIP), and heat treating. The methods avoid remelting of the metal alloy and avoid metal alloy cooling rates of greater than about 100° F. per minute. For example, the exemplary methods avoid the use of directed energy beam additive manufacturing processes such as electron beam melting (EBM) and direct metal laser fusion (DMLF).
This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
The exemplary embodiments will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the inventive subject matter or the application and uses of the inventive subject matter. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.
It has been found that fabricating Ni—Cr—W—Mo alloys with additive manufacturing technology has not been successful thus far using directed energy methods such as direct metal laser sintering (DMLS) or electron beam melting (EBM), apparently due to the rapid thermal gradients and chemistry of the alloy.
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The present disclosure utilizes binder jet printing (BJP) technology to produce near-net shape components directly from Ni—Cr—W—Mo alloys that cannot be easily welded. Using BJP technology enables the component to be formed layer by layer without the application of heat, thus avoiding many of the deficiencies in the prior art utilizing directed energy method, which result in rapid thermal gradients and associated deformation and cracking. The BJP process involves building or printing components layer by layer derived from an original 3D or CAD file. The BJP process employed in the present disclosure uses two materials: a Ni—Cr—W—Mo metal powder based material and a binder. The binder is applied as a liquid and functions as an adhesive between two metal powder layers. The printer passes over the build surface and deposits the binder on relevant build areas based on information from the original 3D or CAD file. The printing process is repeated layer by layer until the component is formed in accordance with the original 3D or CAD file.
Because printing and binding of the metal powder occur at room temperatures, there are no rapid thermal gradients like those common when utilizing laser based or electron beam based powder bed fusion methods. Also, because the embodiments disclosed herein do not utilize melting during building, components can be produced with very fine geometric detail and tolerances. Furthermore, the present disclosure enables the production of complex geometries in a single operation without tooling and enables detailed near-net geometric features that prior art processing methods cannot produce. In particular, the present disclosure utilizes powders that are relatively small in grain size, such as a grain size range of about 5 to about 22 microns and a d50 grain size average of about 10 to about 13 microns, which results in finer detail in the finished printed component.
Furthermore, unlike prior art DMLS or EBM methods, the presently-described methods utilize no directed energy beams to create a component from Ni—Cr—W—Mo alloys. Rather, the exemplary methods utilize a binder jet printing free-form additive manufacturing process to deposit a binder and the metal powder across the surface of the build plane to build a component by applying one layer of powder and one layer of binder per pass. Thus, the rapid solidification rates that result in cracking are avoided. In addition, distortion from powder bed process temperatures are eliminated, and support structures to minimize build cracking from thermal gradients are no longer needed. This results in more economical builds and in more robust builds over the prior art methods. Furthermore, the present disclosure enables parts to be formed closer to near-net where appropriate, which eliminates expensive machining costs associated with prior art post-build processes.
Exemplary methods for manufacturing an article include providing a metal alloy in powdered form. The metal alloy is a nickel-chromium-tungsten-molybdenum alloy. Such alloys have the properties of good high-temperature strength, resistance to oxidizing environments up to 2100° F. (1149° C.) for prolonged exposures, resistance to nitriding environments, and good long-term thermal stability. Furthermore, such alloys include lower thermal expansion characteristics than most high-temperature alloys, and a pronounced resistance to grain coarsening with prolonged exposure to high temperatures.
Ni—Cr—W—Mo alloys in accordance with some embodiments of the present disclosure may be characterized by the following composition (TABLE 1), in weight-%:
Ni—Cr—W—Mo alloys in accordance with other embodiments of the present disclosure may be characterized by the following composition (TABLE 2), in weight-%:
The powdered form of the Ni—Cr—W—Mo alloy is produced by combining the various constituents (metals and other elements) of the alloy into a mixture, melting the mixture, and atomizing the melted mixture to form a powder, a process which is well-known in the art. The powdered form suitable for use in accordance with embodiments of the present disclosure may be characterized by a grain size range of about 5 to about 22 microns and a d50 grain size average of about 10 to about 13 microns, such as a grain size of about 10 to about 17 microns and a d50 grain size average of about 11 to about 12 microns. Powders that are characterized by this relatively small in grain size enable finer detail in the finished printed component. It should also be noted that the present disclosure desirably may utilize an alloy with very low silicon content, such as less than about 0.2% by weight, because casting and welding are not employed, and silicon is necessary for improved fluidity in casting and welding.
The BJP process involves building or printing components layer by layer derived from an original 3D or CAD file. The BJP process employed in the present disclosure uses two materials: a Ni—Cr—W—Mo metal powder based material and a binder. The binder is applied as a liquid and functions as an adhesive between two metal powder layers. The printer passes over the build surface and deposits the binder on relevant build areas based on information from the original 3D or CAD file. The printing process is repeated layer by layer until the component is formed in accordance with the original 3D or CAD file.
In operation, the binder jet printing apparatus 200 operates in the following manner: First, the powder material 201 is spread over the build platform 204 using the roller 205. Next, the print head 203 deposits the binder adhesive 202 on top of the powder 201 where required. Next, the build platform 204 is lowered by the article's (206) layer thickness, which may be from about 10 to about 150 microns, such as from about 10 to about 100 microns, and for example from about 10 to about 50 microns. Next, another layer of powder 201 is spread over the previous layer. The article 206 is formed where the powder 201 is bound to the liquid binder 202. The unbound powder 201 remains in position surrounding the article 206. The process is repeated until the entire article 206 has been made.
Binder jet printing utilizes no directed energy beams to create the article 206 from Ni—Cr—W—Mo alloys. Thus, the rapid solidification rates that result in microfissuring and cracking are avoided. In addition, distortion from powder bed process temperatures are eliminated, and support structures to minimize build cracking from thermal gradients are not needed. Binder jet printing is performed at room temperature. Moreover, binder jet printing does not require the use of a shielding gas, and accordingly there is reduced risk of gas entrapment in the finished article 206. Still further, there is no remelting of the article 206 after it has been manufactured.
According to various embodiments, exemplary methods for manufacturing an article include providing a three-dimensional computer model of the article. The exemplary methods further include, at the binder jet printing apparatus 200, supplying the Ni—Cr—W—Mo metal alloy and loading the three-dimensional model, and, using the binder jet printing apparatus, manufacturing the article in accordance with the loaded three-dimensional model in a layer-by-layer manner with the supplied metal alloy, as described above. Still further, the exemplary methods include performing one or more post-print processes selected from the group of: curing, powder removal, de-binding, sintering, hot isostatic pressing (HIP), and heat treating.
Method 300 continues at step 303 with the fabrication of the article at the binder jet printing apparatus, as described above. After fabrication, a curing process 304 is employed to cure the article, which may be performed at an elevated temperature over a period of time. Method 300 then continues at step 305 wherein the cured article is cleaned and/or has any excess powder removed. Thereafter, a de-binding process 306 may be employed to remove the residual binder from the article. The nature of de-binding depends on the type of binder employed, but may generally involve the use of subjecting the article to elevated temperatures, such as at least about 200° F., and/or reduced pressures.
Method 300 continues at step 307 where the article is sintered. Sintering involves the use of elevated temperatures, such as at least about 2000° F., to coalesce the powdered material into a solid mass, but without liquefaction. Sintering ensures adequate densification of the article. After sintering, the article may be inspected at step 308 to ensure that the solidified mass meets the appropriate design specifications and tolerances. As is conventional with turbine engine components, the article may thereafter be subjected to hot-isostatic pressing (HIP) at step 309 to remove any internal defects of faults, and/or further heat treated at step 310 as necessary to achieve an appropriate material phase constituency of the article.
Method 300 thereafter proceeds to any applicable post-build operations at step 311, such as machining the article to final specifications. The completed article may thereafter be inspected at step 312. If the inspection reveals no defects, the article may be shipped at step 313 to an appropriate facility for assembling a gas turbine engine (or other system), as per its intended use. It is therefore noted that none of the method steps of method 300 employ the use of directed energy additive manufacturing processes, such as DMLS or EMB. As such, the method avoids remelting of the metal alloy and avoids metal alloy cooling rates of greater than about 100° F. per minute.
Accordingly, the present disclosure has provided methods that utilize binder jet printing technology to produce near-net shape components directly from Ni—Cr—W—Mo alloys that cannot be easily welded. Thus, the rapid solidification rates that appear to result in cracking are avoided. In addition, distortion from powder bed process temperatures is eliminated, and support structures to minimize build cracking from thermal gradients are no longer needed. This results in more economical builds and in more robust builds. Furthermore, the present disclosure has provided methods that enable parts to be formed closer to near-net where appropriate, which eliminates expensive machining costs associated with prior art post-build processes.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the disclosure as set forth in the appended claims and the legal equivalents thereof.
