The present invention relates generally to powder metallurgy and, more particularly, to powder mixtures and methods for preparing powder mixtures, which contain ceramic particles uniformly dispersed within superalloy particles and which are well-suited for producing articles having improved performance characteristics under high temperature operating conditions.
High temperature components (that is, components exposed to temperature exceeding about 1000° F. or about 540° C. during operation) are commonly fabricated by powder metallurgy and, specifically, by sintering superalloy powders to produce a solid body, which may then undergo further processing to produce the finished component. Components produced from sintered superalloy powders may have thermal tolerances greatly exceeding those of other metals and alloys. However, components produced by sintering conventionally-known superalloy powders may still have hardness, fatigue resistance, and wear resistance properties that are undesirably limited in certain applications, such as when such powders are used to produce the rings of a rolling element bearing deployed within a high temperature operating environment. While high temperature ceramic materials can be utilized to produce articles having improved hardness and wear resistance under elevated operating temperatures, the toughness and ductility of high temperature ceramic materials tend to be relatively poor. Consequently, such ceramic materials may be undesirably brittle and fracture prone when utilized to produce high temperature bearing rings or other components subject to severe loading conditions during high temperature operation. Furthermore, additional design modifications to the high temperature components may be required if fabricated from relatively brittle ceramic materials.
It would thus be desirable to provide embodiments of a method for producing enhanced superalloy powders or powder mixtures that, when sintered and otherwise processed, yield high temperature articles having excellent hardness and wear resistant properties, while also having relatively high ductility and fracture resistance. It would also be desirable if, in at least some embodiments, the method could further be utilized to prepare enhanced superalloy powder mixtures able to produce high temperature articles having other improved characteristics as compared to articles produced from other, conventionally-known superalloy powders. For example, it would be desirable if embodiments of the method could produce an enhanced superalloy powder mixture having increased strength under high temperature operating conditions when sintered into a chosen article, such as a turbine blade, vane, nozzle, duct, or other high temperature component deployed within a gas turbine engine. Other desirable features and characteristics of embodiments of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying drawings and the foregoing Background.
Embodiments of a method for producing powder mixtures having uniform dispersion of ceramic particles within superalloy particles are provided. In one embodiment, the method includes producing an initial powder mixture comprising ceramic particles mixed with superalloy mother particles having an average diameter larger than the average diameter of the ceramic particles. The initial powder mixture is preferably prepared utilizing a resonant acoustic mixing process, a milling process, or other process capable of producing a powder mixture wherein the ceramic particles are substantially uniformly or evenly dispersed throughout the powder mixture. The initial powder mixture is formed into a consumable solid body. At least a portion of the consumable solid body is gradually melted, while the consumable solid body is rotated at a rate of speed sufficient to cast-off a uniformly dispersed powder mixture in which the ceramic particles are embedded within the superalloy mother particles.
In another embodiment, the method is carried-out utilizing a consumable solid body composed of ceramic particles mixed with superalloy mother particles having an average diameter larger than the average diameter of the ceramic particles. Similar to the embodiment above, the method includes the process or step of gradually melting at least a portion of the consumable solid body, while rotating the consumable solid body at a rate of speed sufficient to cast-off a uniformly dispersed powder mixture in which the ceramic particles are embedded within the superalloy mother particles.
Embodiments of a superalloy powder mixture are also provided. In one embodiment, the superalloy powder mixture include a superalloy powder comprising a plurality of superalloy mother particles. Ceramic particles are distributed throughout the superalloy powder and having an average diameter less than (e.g., at least 100 times less than) that of the superalloy mother particles. At least a majority of the ceramic particles may be embedded within the superalloy mother particles. Additionally, the superalloy powder mixture may consist essentially of at least 85% superalloy powder, by weight, with the remainder particulate ceramic materials in further embodiments.
At least one example of the present invention will hereinafter be described in conjunction with the following figures, wherein like numerals denote like elements, and:
The following Detailed Description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding Background or the following Detailed Description.
As appearing herein, the term “superalloy” is utilized to denote a material containing two or more metals and having an operative thermal tolerance exceeding about 1000° F. or about 540° C. As further appearing herein, the term “nanoparticle” refers a particle having a diameter or other cross-sectional dimension greater than 0.1 nanometer (nm) and less than 1 micron (μm). The term “ceramic” is utilized to refer to an inorganic, non-metallic material, whether amorphous or crystalline, such as an oxide or non-oxide of the type described below. Finally, the descriptor “uniformly dispersed” is utilized in a relative sense to refer to a powder mixture containing superalloy mother particles in which ceramic particles (e.g., ceramic nanoparticles) have been embedded wherein, due to the infiltration of the ceramic particles into the mother particles, the distribution of the ceramic particles throughout the powder mixture is made more uniform or homogenous than would otherwise be the case if the ceramic particles were not embedded into the mother particles: that is, if the below-described dispersion or particle infiltration process were not performed (see, for example, the description set-forth below in conjunction with STEP 34 of exemplary method 20 shown in
As described in the foregoing section entitled “BACKGROUND,” there exists an ongoing need for enhanced superalloy powder or powder mixtures suitable for usage in the production of articles or components having enhanced performance characteristics under high temperature (e.g., >˜1000° F. or >˜540° C.) conditions as compared to components fabricated from other known high temperature materials, such as conventionally-known superalloy powders and ceramic materials. Such enhanced performance characteristics may include, but are not necessarily limited to, improved hardness, fatigue resistance, wear resistance, toughness (fracture resistance), ductility, and/or strength properties under high temperature operating conditions. The enhanced superalloy powder mixtures described herein are consequently well-suited for producing high temperature articles wherein such properties are of particular value. For example, in embodiments wherein the powder mixture is formulated to provide improved hot hardness, fatigue resistance, wear resistance, and toughness, the powder mixture may be particularly well-suited for use in the production of high temperature bearing rings or bushings. As a second example, in embodiments wherein the enhanced superalloy powder mixture is formulated to provide increased strength over an expanded temperature range as compared conventional superalloy powders, the powder mixture may be advantageously employed to produce gas turbine engine components exposed to combustive gas flow during engine operation, such as turbine blades, vanes, ducts, nozzles, and the like.
Embodiments of the enhanced superalloy powder are preferably produced from an initial powder mixture containing one or more pre-existing superalloy powders mixed with one or more types of ceramic particles. It is preferred that the ceramic particles have an average diameter in the nanometer range (the nanometer range between 1 nm and 1 μm, and the preferred ceramic particle sizes falling within this range set-forth below); however, in certain embodiments, the ceramic particles may have an average diameter in the low micron range and, specifically, between 1 μm and 5 μm. In any event, the ceramic particles will have average diameters less than the metallic particles of which the superalloy powder is composed. For this reason, the ceramic particles may be referred to as the “smaller ceramic particles” herein, while the particles of the superalloy powders may be referred to as the “larger superalloy particles” or as “superalloy mother particles.” Additionally, in preferred embodiments wherein the average diameter of the ceramic particles falls within the nanometer range, the ceramic particles may be referred to herein as “ceramic nanoparticles.”
As will be described in detail below, the initial mixture of the pre-existing superalloy powder and the smaller ceramic particles are processed in a manner whereby the ceramic particles are uniformly dispersed throughout the final powder mixture. Notably, by virtue of the below described dispersion process, the ceramic particles become largely or wholly embedded within the larger metallic particles of the superalloy powder. The end result is uniformly dispersed, particle-infiltrated powder mixture, which may be utilized to produce articles having superior hot hardness, fatigue resistance, wear resistance, toughness (fracture resistance), ductility, and/or strength properties under highly elevated temperatures. The enhanced powder mixture produced pursuant the below-described fabrication process may consist essentially of ceramic particles, and preferably ceramic nanoparticles, dispersed throughout the larger superalloy particles; or, instead, may include other constituents (e.g., additional hard wear particles) in certain embodiments.
It is, of course, possible to simply utilize the initial powder mixture (that is, a mixture of a chosen superalloy powder and smaller ceramic particles) to produce high temperature articles by powder metallurgy. However, within the initial powder mixture, the smaller ceramic particles are largely concentrated at the boundaries of the larger superalloy particles or in the free space between the superalloy particles. As a result, the smaller ceramic particles may interfere with proper sintering of the superalloy particles and may themselves conglomerate during processing. Conglomeration of the ceramic particles results in larger particles, which can coarsen the microstructure of the high temperature article resulting in decreased ductility, increased brittleness, and a greater likelihood of fracture when subject to severe loading or vibratory conditions. Such a reduction in ductility may occur even in the absence of ceramic particle conglomeration due to the relatively non-homogenous distribution of the smaller ceramic particles throughout the powder mixture and, specifically, due to the relatively high concentrations of ceramic particles at the interfaces between the superalloy particles. In contrast, by infiltrating the superalloy mother particles with the smaller ceramic particles under process conditions minimizing conglomeration of the smaller ceramic particles, a powder mixture can be produced wherein the ceramic particles are more uniformly dispersed throughout the powder mixture to mitigate, if not wholly overcome, the foregoing limitations.
A non-exhaustive list of ceramic particles that may be contained in the initial powder mixture includes oxides, such as alumina and zirconia; non-oxides, such as carbides, borides, nitrides, and silicides; and combinations thereof. In preferred embodiments, the initial powder mixture contains carbide and/or oxide particles or nanoparticles. The particular type or types of ceramic particles or nanoparticles combined with the pre-existing superalloy powder to yield the initial powder mixture will typically be chosen based upon the desired properties of the high temperature articles to be produced therefrom. In instances wherein the high temperature article is desirably imparted with superior hardness and wear resistance properties, while also having a relatively high toughness (fracture resistance) and ductility, it is preferred that carbide, nitride, and/or boride particles are included within initial powder mixture. Of the foregoing list, it may be especially preferably that carbide particles, such as tungsten carbide or titanium carbide particles, are contained within the initial powder mixture. By comparison, in instances wherein the high temperature article is desirably imparted with an increased strength, it is preferred that oxide (e.g., alumina or zirconia) particles are included within the initial powder mixture. In this latter case, the strength of the high temperature article may be increased under high temperature (e.g., >˜1000° F. or >˜540° C.) operating conditions as compared to simply producing the high temperature article from the superalloy powder itself.
The ratio of ceramic particles to superalloy mother particles contained within the powder mixture will vary amongst different embodiments in relation to the desired properties of the high temperature articles produced from the final (uniformly dispersed) powder mixture. Generally, it may be preferred that the initial powder mixture contains less than about 10%, by weight (wt %), of the ceramic particles. It has been found that, above this upper threshold, undesired conglomeration of the ceramic particles may occur during mixing. At the same time, in instances wherein a hard, wear resistant (e.g., a carbide, nitride, or boride) particle is included within the powder mixture, it will often be desirable to maximize the particle content or “fill rate” within the initial powder mixture without exceeding this upper threshold. Thus, in such cases, it generally may be preferred that the powder mixture contains between about 5 wt % and about 10 wt % of the ceramic particles. Conversely, in instances wherein an oxide particle or nanoparticle is included within the powder mixture for superalloy-strengthen purposes, the ceramic particle content of the initial powder mixture may be considerably lower; e.g., in one embodiment, the powder mixture may contain less than about 2 wt % and, preferably, between about 0.5 wt % and about 1.0 wt % of the oxide particles or nanoparticles. The foregoing examples notwithstanding, the initial powder mixture may contain greater or lesser amounts of ceramic particles of the aforementioned ranges (e.g., greater than 10 wt % ceramic particles) in further embodiments.
The respective shapes of the smaller ceramic particles and larger superalloy mother particles may vary, but are preferably both generally spherical. As indicated above, the superalloy mother particles are considerably larger than the ceramic particles. In preferred embodiments, the ceramic nanoparticles are used, which, by definition, have an average diameter less than 1 μm. In one embodiment, the average diameter of the superalloy mother particles is at least 100 times and may be over 500 times the average diameter of the smaller (e.g., nanometer or low micron range) ceramic particles included within the initial powder mixture. By way of example, the ceramic particles may have an average diameter less than about 5 μm; more preferably, between about 5 and about 500 nm; and, still more preferably, between about 10 and about 100 nm. By comparison, the superalloy mother particles preferably have an average diameter less than about 50 μm and, perhaps, between about 10 and about 50 μm. In certain embodiments, minimizing the size of the superalloy mother particle may advantageously allow the fill rate of the ceramic particles to be favorably increased while avoiding conglomeration of the ceramic particles during the below-described mixing process. In further embodiments, the superalloy and ceramic particle size may be greater than or less than the aforementioned ranges.
The initial powder mixture is ideally produced as a substantially uniform blend of the selected superalloy powder (or powders) and the smaller ceramic particles or nanoparticles. Different mixing techniques can be employed for producing such a substantially uniform powder blend including, but not limited to, ball milling and roll milling. In preferred implementations, a Resonant Acoustic Mixing (“RAM”) process is employed. During such a RAM process, the powders may be loaded into the chamber of a resonant acoustic mixture. When activated, the RAM mixer rapidly oscillates the chamber and the powders contained therein over a selected displacement range and at a selected frequency. Advantageously, such a RAM process can produce a substantially uniform powder mixture in a relatively short period of time (e.g., on the order of minutes) relative to milling processes, which may require much longer mixing periods to produce a comparable mixture (e.g., on the order of days). In certain embodiments, such as when the initial powder mixture has a relatively high ceramic particle content (e.g., a fill rate approaching or exceeding 10 wt %), it may be desirable to place mixing media (e.g., zirconia balls) within the RAM chamber during mixing. Additionally or alternatively, it may be desirable to add a relatively small amount of water or another liquid to transform the powder mixture into a slurry during the mixing process to further decrease the likelihood of ceramic particle conglomeration.
Continuing with exemplary method 20, the initial powder mixture (e.g., powder mixture 24 shown in
Next, at STEP 32 of exemplary method 20 (
Preparation of the uniformly dispersed, particle-infiltrated powder mixture may conclude after STEP 32 (
By virtue of the above-described process, a uniformly dispersed, particle-infiltrated powder mixture has now been produced. In some embodiments, the uniformly dispersed powder mixture may consist essentially of the superalloy powder and ceramic particles. In other embodiments, the uniformly dispersed powder mixture may contain other constituents in powder form, such as hard wear particles added after the above-described particle infiltration process. In some embodiments, the uniformly dispersed powder mixture may contain or consist essentially of at least 85 wt % superalloy powder and between 0.1 and 10 wt % of ceramic particles or nanoparticles. In other embodiments, the uniformly dispersed powder mixture may contain or consist essentially of at least 85 wt % superalloy powder and the remainder particulate ceramic materials, whether present solely in the form of nanoparticles or present in the form of both nanoparticles and larger particles, such as hard wear particles 38 shown in
Referring once again to
Various different high temperature articles or components may be produced from the uniformly dispersed powder mixture during STEP 40 (
The foregoing has thus provided embodiments of a method for producing superalloy powder mixtures suitable for usage in the production of articles or components having enhanced performance characteristics under high temperature operating conditions. The superalloy powder mixtures described herein include ceramic particles, such as ceramic nanoparticles, relatively uniformly dispersed throughout a superalloy powder including within the individual mother particles making-up the superalloy powder. In accordance with further embodiments of the method described herein, the superalloy powder mixture can be processed utilizing conventionally-known metallurgical techniques to produce high temperature articles composed of a superalloy matrix throughout which the smaller ceramic particle, such as ceramic nanoparticles, are distributed.
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 invention in any way. Rather, the foregoing Detailed Description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set-forth in the appended claims.
This application is a divisional of co-pending U.S. patent application Ser. No. 14/036,373, filed Sep. 25, 2013.
Number | Date | Country | |
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Parent | 14036373 | Sep 2013 | US |
Child | 15402442 | US |