Patent Application
20090293672
The present disclosure relates to improved articles including cemented hard particles and methods of making such articles.
Materials composed of cemented hard particles are technologically and commercially important. Cemented hard particles include a discontinuous dispersed phase of hard metallic (i.e., metal-containing) and/or ceramic particles embedded in a continuous metallic binder phase. Many such materials possess unique combinations of abrasion and wear resistance, strength, and fracture toughness.
Terms used herein have the following meanings. “Strength” is the stress at which a material ruptures or fails. “Fracture toughness” is the ability of a material to absorb energy and deform plastically before fracturing. “Toughness” is proportional to the area under the stress-strain curve from the origin to the breaking point. See McGraw Hill Dictionary of Scientific and Technical Terms (5th ed. 1994). “Wear resistance” is the ability of a material to withstand damage to its surface. “Wear” generally involves progressive loss of material due to a relative motion between a material and a contacting surface or substance. See Metals Handbook Desk Edition (2d ed. 1998).
The dispersed hard particle phase typically includes grains of, for example, one or more of a carbide, a nitride, a boride, a silicide, an oxide, and solid solutions of any of these types of compounds. Hard particles commonly used in cemented hard particle materials are metal carbides such as tungsten carbide and, thus, these materials are often referred to generically as “cemented carbides.” The continuous binder phase, which binds or “cements” the hard particles together, generally includes, for example, at least one of cobalt, cobalt alloy, nickel, nickel alloy, iron and iron alloy. Additionally, alloying elements such as, for example, chromium, molybdenum, ruthenium, boron, tungsten, tantalum, titanium, and niobium may be included in the binder phase to enhance particular properties. The various commercially available cemented carbide grades differ in terms of at least one property such as, for example, composition, grain size, or volume fractions of the discontinuous and/or continuous phases.
For certain applications parts formed from cemented hard particles may need to be attached to parts formed of different materials such as, for example, steels, nonferrous metallic alloys, and plastics. Techniques that have been used to attach such parts include metallurgical techniques such as, for example, brazing, welding, and soldering, and mechanical techniques such as, for example, press or shrink fitting, application of epoxy and other adhesives, and mating of mechanical features such as threaded coupling and keyway arrangements.
Problems are encountered when attaching cemented hard particle parts to parts formed of steels or nonferrous alloys using conventional metallurgical or mechanical techniques. The difference in coefficient of thermal expansion (CTE) between cemented carbide materials and most steels (as well as most nonferrous alloys) is significant. For example, the CTE of steel ranges from about 10×10−6 in/in/° K to 15×10−6 in/in/° K, which is about twice the range of about 5×10−6 in/in/° K to 7×10−6 in/in/° K CTE for a cemented carbide. The CTE of certain nonferrous alloys exceeds that of steel, resulting in an even more significant CTE mismatch. If metallurgical bonding techniques such as brazing or welding are employed to attach a cemented carbide part to a steel part, for example, enormous stresses may develop at the interface between the parts during cooling due to differences in rates of part contraction. These stresses often result in the development of cracks at and near the interface of the parts. These defects weaken the bond between the cemented hard particle region and the metal or metallic region, and also the attached regions of the parts themselves.
In general, it is usually not practical to mechanically attach cemented hard particle parts to steel or other metallic parts using threads, keyways or other mechanical features because the fracture toughness of cemented carbides is low relative to steel and other metals and metallic alloys. Moreover, cemented carbides, for example, are highly notch-sensitive and susceptible to premature crack formation at sharp corners. Comers are difficult to avoid including in parts when designing mechanical features such as threads and keyways on the parts. Thus, the cemented hard particle parts can prematurely fracture in the areas incorporating the mechanical features.
The technique described in U.S. Pat. No. 5,359,772 to Carlsson et al. attempts to overcome certain difficulties encountered in forming composite articles having a cemented carbide region attached to a metal region. Carlsson teaches a technique of spin-casting iron onto pre-formed cemented carbide rings. Carlsson asserts that the technique forms a “metallurgical bond” between the iron and the cemented carbide. The composition of the cast iron in Carlsson must be carefully controlled such that a portion of the austenite forms bainite in order to relieve the stresses caused by differential shrinkage between the cemented carbide and the cast iron during cooling from the casting temperature. However, this transition occurs during a heat treating step after the composite is formed, to relieve stress that already exists. Thus, the bond formed between the cast iron and the cemented carbide in the method of Carlsson may already suffer from stress damage. Further, a bonding technique as described in Carlsson has limited utility and will only potentially be effective when using spin casting and cast iron, and would not be effective with other metals or metal alloys.
The difficulties associated with the attachment of cemented hard particle parts to parts of dissimilar materials, and particularly metallic parts, have posed substantial challenges to design engineers and have limited the applications for cemented hard particle parts. As such, there is a need for improved cemented hard particle-metallic and related materials, methods, and designs.
One non-limiting embodiment according to the present disclosure is directed to a composite sintered powder metal article that includes a first region including cemented hard particles and a second region including at least one of a metal and a metallic alloy. The metal or metallic alloy is selected from a steel, nickel, a nickel alloy, titanium, a titanium alloy, molybdenum, a molybdenum alloy, cobalt, a cobalt alloy, tungsten, and a tungsten alloy. The first region is metallurgically bonded to the second region, and the second region has a thickness greater than 100 microns.
Another non-limiting embodiment according to the present disclosure is directed to a method of making a composite sintered powder metal article. The method includes providing a first powder in a first region of a mold, and providing a second powder in a second region of the mold, wherein the second powder contacts the first powder. The first powder includes hard particles and a powdered binder. The second powder includes at least one of a metal powder and a metallic alloy powder selected from a steel powder, a nickel powder, a nickel alloy powder, a molybdenum powder, a molybdenum alloy powder, a titanium powder, a titanium alloy powder, a cobalt powder, a cobalt alloy powder, a tungsten powder, and a tungsten alloy powder. The method further includes consolidating the first powder and the second powder in the mold to provide a green compact. The green compact is sintered to provide a composite sintered powder metal article including a first region metallurgically bonded to a second region. The first region includes a cemented hard particle material formed on sintering the first powder. The second region includes a metal or metallic alloy formed on sintering the second powder.
Features and advantages of the subject matter described herein may be better understood by reference to the accompanying figures in which:
In the present description of non-limiting embodiments and in the claims, other than in the operating examples or where otherwise indicated, all numbers expressing quantities or characteristics of ingredients and products, processing conditions, and the like are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, any numerical parameters set forth in the following description and the attached claims are approximations that may vary depending upon the desired properties one seeks to obtain in the subject matter described in the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.
Certain embodiments according to the present disclosure are directed to composite sintered powder metal articles. A composite article is an object that comprises at least two regions, each region composed of a different material. Composite sintered powder metal articles according to the present disclosure include at least a first region, which includes cemented hard particles, metallurgically bonded to a second region, which includes at least one of a metal and a metallic alloy. Two non-limiting examples of composite articles according to the present disclosure are shown in
As it is known in the art sintered powder metal material is produced by pressing and sintering masses of metallurgical powders. In a conventional press-and-sinter process, a metallurgical powder blend is placed in a void of a mold and compressed to form a “green compact.” The green compact is sintered, which densifies the compact and metallurgically bonds together the individual powder particles. In certain instances, the compact may be consolidated during sintering to full or near-full theoretical density.
In composite articles according to the present disclosure, the cemented hard particles of the first region are a composite including a discontinuous phase of hard particles dispersed in a continuous binder phase. The metal and/or metallic alloy included in the second region is one or more selected from a steel, nickel, a nickel alloy, titanium, a titanium alloy, molybdenum, a molybdenum alloy, cobalt, a cobalt alloy, tungsten, and a tungsten alloy. The two regions are formed from metallurgical powders that are pressed and sintered together. During sintering, a metallurgical bond forms between the first and second regions, for example, at the interface between the cemented hard particles in the first region and the metal and/or metallic alloy in the second region.
The present inventors determined that the metallurgical bond that forms between the first region (including cemented hard particles) and the second region (including at least one of a metal and a metallic alloy) during sintering is surprisingly and unexpectedly strong. In various embodiments produced according to the present disclosure, the metallurgical bond between the first and second regions is free from significant defects, including cracks and brittle secondary phases. Such bond defects commonly are present when conventional techniques are used to bond a cemented hard particle material to a metal or metallic alloy. The metallurgical bond formed according to the present disclosure forms directly between the first and second regions at the microstructural level and is significantly stronger than bonds formed by prior art techniques used to bind together cemented carbides and metal or metallic alloys, such as, for example, the casting technique discussed in U.S. Pat. No. 5,359,772 to Carlsson. The method of Carlsson involving casting a molten iron onto cemented hard particles does not form a strong bond. Molten iron reacts with cemented carbides by chemically reacting with the tungsten carbide particles and forming a brittle phase commonly referred to as eta-phase. The interface is thus weak and brittle. The bond formed by the technique described in Carlsson is limited to the relatively weak bond that can be formed between a relatively low-melting molten cast iron and a pre-formed cemented carbide. Further, this technique only applies to cast iron as it relies on an austenite to bainite transition to relieve stress at the bond area.
The metallurgical bond formed by the present press and sinter technique using the materials recited herein avoids the stresses and cracking experienced with other bonding techniques. The strong bond formed according to the present disclosure effectively counteracts stresses resulting from differences in thermal expansion properties of the bonded materials, such that no cracks form in the interface between the first and second regions of the composite articles. This is believed to be at least partially a result of the nature of the unexpectedly strong metallurgical bond formed by the technique of the present disclosure, and also is a result of the compatibility of the materials discovered in the present technique. It has been discovered that not all metals and metallic alloys can be sintered to cemented hard particles such as cemented carbide.
In certain embodiments according to the present disclosure, the first region comprising cemented hard particles has a thickness greater than 100 microns. Also, in certain embodiments, the first region has a thickness greater than that of a coating.
In certain embodiments according to the present disclosure, the first and second regions each have a thickness greater than 100 microns. In certain other embodiments, each of the first and second regions has a thickness greater than 0.1 centimeters. In still other embodiments, the first and second regions each have a thickness greater than 0.5 centimeters. Certain other embodiments according to the present disclosure include first and second regions having a thickness of greater than 1 centimeter. Still other embodiments comprise first and second regions having a thickness greater than 5 centimeters. Also, in certain embodiments according to the present disclosure, at least the second region or another region of the composite sintered powder metal article has a thickness sufficient for the region to include mechanical attachment features such as, for example, threads or keyways, so that the composite article can be attached to another article via the mechanical attachment features.
The embodiments described herein achieve an unexpectedly and surprisingly strong metallurgical bond between the first region (including cemented hard particles) and the second region (including at least one of metal and a metallic alloy) of the composite article. In certain embodiments according to the present disclosure, the formation of the superior bond between the first and second regions is combined with incorporating advantageous mechanical features, such as threads or keyways, on the second region of the composite to provide a strong and durable composite article that may be used in a variety of applications or adapted for connection to other articles for use in specialized applications.
In other embodiments according to the present disclosure, a metal or metallic alloy of the second region has a thermal conductivity less than a thermal conductivity of the cemented hard particle material of the first region, wherein both thermal conductivities are evaluated at room temperature (20° C.). Without being limited to any specific theory, it is believed that the metal or metallic alloy of the second region must have a thermal conductivity that is less than a thermal conductivity of the cemented hard particle material of the first region in order to form a metallurgical bond between the first and second regions having sufficient strength for certain demanding applications of cemented hard particle materials. In certain embodiments, only metals or metallic alloys having thermal conductivity less than a cemented carbide may be used in the second region. In certain embodiments, the second region or any metal or metallic alloy of the second region has a thermal conductivity less than 100 W/mK. In other embodiments, the second region or any metal or metallic alloy of the second region may have a thermal conductivity less than 90 W/mK.
In certain other embodiments according to the present disclosure, the metal or metallic alloy of the second region of the composite article has a melting point greater than 1200° C. Without being limited to any specific theory, it is believed that the metal or metallic alloy of the second region must have a melting point greater than 1200° C. so as to form a metallurgical bond with the cemented hard particle material of the first region with bond strength sufficient for certain demanding applications of cemented hard particle materials. In other embodiments, the metal or metallic alloy of the second region of the composite article has a melting point greater than 1275° C. In some embodiments, the melting point of the metal or metallic alloy of the second region is greater than a cast iron.
According to the present disclosure, the cemented hard particle material included in the first region must include at least 60 percent by volume dispersed hard particles. If the cemented hard particle material includes less than 60 percent by volume of hard particles, the cemented hard particle material will lack the required combination of abrasion and wear resistance, strength, and fracture toughness needed for applications in which cemented hard particle materials are used. See Kenneth J. A. Brookes, Handbook of Hardmetals and Hard Materials (International Carbide Data, 1992). Accordingly, as used herein, “cemented hard particles” and “cemented hard particle material” refer to a composite material comprising a discontinuous phase of hard particles dispersed in a continuous binder material, and wherein the composite material includes at least 60 volume percent of the hard particle discontinuous phase.
In certain embodiments of the composite article according to the present disclosure, the metal or metallic alloy of the second region may include from 0 up to 50 volume percent of hard particles (based on the volume of the metal or metallic alloy). The presence of certain concentrations of such particles in the metal or metallic alloy may enhance wear resistance of the metal or alloy relative to the same material lacking such hard particles, but without significantly adversely affecting machineability of the metal or metallic alloy. Obviously, the presence of up to 50 volume percent of such particles in the metallic alloy does not result in a cemented hard particle material, as defined herein, for at least the reason that the hard particle volume fraction is significantly less than in a cemented hard particle material. In addition, it has been discovered that in certain composite articles according to the present disclosure, the presence of hard particles in the metal or metallic alloy of the second region may modify the shrinkage characteristics of the region so as to more closely approximate the shrinkage characteristics of the first region. In this way, the CTE of the second region may be adjusted to better ensure compatibility with the CTE of the first region to prevent formation of stresses in the metallurgical bond region that could result in cracking.
Thus, in certain embodiments according to the present disclosure, the metal or metallic alloy of the second region of the composite article includes from 0 up to 50 percent by volume, and preferably no more than 20 to 30 percent by volume hard particles dispersed in the metal or metallic alloy. The minimum amount of hard particles in the metal or metallic alloy region that would affect the wear resistance and/or shrinkage properties of the metal or metallic alloy is believed to be about 2 to 5 percent by volume. Thus, in certain embodiments according to the present disclosure, the metal or metallic alloy of the second region of the composite article includes from 2 to 50 percent by volume, and preferably from 2 to 30 percent by volume hard particles dispersed in the metal or metallic alloy. Other embodiments may include from 5 to 50 percent hard particles, or from 5 to 30 percent by volume hard particles dispersed in the metal or metallic alloy. Still other embodiments may comprise from 2 to 20, or from 5 to 20 percent by volume hard particles dispersed in the metal or metallic alloy. Certain other embodiments may comprise from 20 to 30 percent by volume hard particles by volume dispersed in the metal or metallic alloy.
The hard particles included in the first region and, optionally, the second region may be selected from, for example, the group consisting of a carbide, a nitride, a boride, a silicide, an oxide, and mixtures and solid solutions thereof. In one embodiment, the metal or metallic alloy of the second region includes up to 50 percent by volume of dispersed tungsten carbide particles.
In certain embodiments according to the present disclosure, the dispersed hard particle phase of the cemented hard particle material of the first region may include one or more hard particles selected from a carbide, a nitride, a boride, a silicide, an oxide, and solid solutions thereof. In certain embodiments, the hard particles may include carbide particles of at least one transition metal selected from titanium, chromium, vanadium, zirconium, hafnium, tantalum, molybdenum, niobium, and tungsten. In still other embodiments, the continuous binder phase of the cemented hard particle material of the first region includes at least one of cobalt, a cobalt alloy, nickel, a nickel alloy, iron, and an iron alloy. The binder also may include, for example, one or more elements selected from tungsten, chromium, titanium, tantalum, vanadium, molybdenum, niobium, zirconium, hafnium, and carbon, up to the solubility limits of these elements in the binder. Additionally, the binder may include up to 5 weight percent of one or more elements selected from copper, manganese, silver, aluminum, and ruthenium. One skilled in the art will recognize that any or all of the constituents of the cemented hard particle material may be introduced into the metallurgical powder from which the cemented hard particle material is formed in elemental form, as compounds, and/or as master alloys.
The properties of cemented hard particle materials, such as cemented carbides, depend on parameters including the average hard particle grain size and the weight fraction or volume fraction of the hard particles and/or binder. In general, the hardness and wear resistance increases as the grain size decreases and/or the binder content decreases. On the other hand, fracture toughness increases as the grain size increases and/or the binder content increases. Thus, there is a trade-off between wear resistance and fracture toughness when selecting a cemented hard particle material grade for any application. As wear resistance increases, fracture toughness typically decreases, and vice versa.
Certain other embodiments of the articles of the present disclosure include hard particles comprising carbide particles of at least one transition metal selected from titanium, chromium, vanadium, zirconium, hafnium, tantalum, molybdenum, niobium, and tungsten. In certain other embodiments, the hard particles include tungsten carbide particles. In still other embodiments, the tungsten carbide particles may have an average grain size of from 0.3 to 10 μm.
The hard particles of the cemented hard particle material in the first region preferably comprise from about 60 to about 98 volume percent of the total volume of the cemented hard particle material. The hard particles are dispersed within a matrix of a binder that preferably constitutes from about 2 to about 40 volume percent of the total volume of the cemented hard particle material.
Embodiments of the composite articles according to the present disclosure may also include hybrid cemented carbides such as, for example, any of the hybrid cemented carbides described in copending U.S. patent application Ser. No. 10/735,379, the entire disclosure of which is hereby incorporated herein by reference. For example, an article according to the present disclosure may comprise at least a first region including a hybrid cemented carbide metallurgically bonded to a second region comprising one of a metal and a metallic alloy. Certain other articles may comprise at least a first region including cemented hard particles, a second region including at least one of a metal and a metallic alloy, wherein the first and third regions are metallurgically bonded to the second region, and a third region including a hybrid cemented carbide material.
Generally, a hybrid cemented carbide is a material comprising particles of at least one cemented carbide grade dispersed throughout a second cemented carbide continuous phase, thereby forming a microscopic composite of cemented carbides. The hybrid cemented carbides of application Ser. No. 10/735,379 have low dispersed phase particle contiguity ratios and improved properties relative to certain other hybrid cemented carbides. Preferably, the contiguity ratio of the dispersed phase of a hybrid cemented carbide included in embodiments according to the present disclosure is less than or equal to 0.48. Also, a hybrid cemented carbide included in the embodiments according to the present disclosure preferably comprises a dispersed phase having a hardness greater than a hardness of the continuous phase of the hybrid cemented carbide. For example, in certain embodiments of hybrid cemented carbides included in one or more regions of the composite articles according to the present disclosure, the hardness of the dispersed phase in the hybrid cemented carbide is preferably greater than or equal to 88 Rockwell A Hardness (HRA) and less than or equal to 95 HRA, and the hardness of the continuous phase in the hybrid carbide is greater than or equal to 78 HRA and less than or equal to 91 HRA.
Additional embodiments of the articles according to the present disclosure may include hybrid cemented carbide in one or more regions of the articles wherein a volume fraction of the dispersed cemented carbide phase is less than 50 volume percent of the hybrid cemented carbide, and wherein the contiguity ratio of the dispersed cemented carbide phase is less than or equal to 1.5 times the volume fraction of the dispersed cemented carbide phase in the hybrid cemented carbide.
Certain embodiments of articles according to the present disclosure include a second region comprising at least one of a metal and a metallic alloy wherein the region includes at least one mechanical attachment feature or other mechanical feature. A mechanical attachment feature, as used herein, enables certain articles according to the present disclosure to be connected to certain other articles and function as part of a larger device. Mechanical attachment features may include, for example, threads, slots, keyways, teeth or cogs, steps, bevels, bores, pins, and arms. It has not previously been possible to successfully include such mechanical attachment features on articles formed solely from cemented hard particles for certain demanding applications because of the limited tensile strength and notch sensitivity of cemented hard particle materials. Prior art articles have included a metal or metallic alloy region including one or more mechanical attachment features that were coupled to a cemented hard particle region by means other than co-pressing and sintering. Such prior art articles suffered from a relatively weak bond between the metal or metallic alloy region and the cemented hard particle region, severely limiting the possible applications of the articles.
The process for manufacturing cemented hard particle parts typically comprises blending or mixing powdered ingredients including hard particles and a powdered binder to form a metallurgical powder blend. The metallurgical powder blend may be consolidated or pressed to form a green compact. The green compact is then sintered to form the article or a portion of the article. According to one process, the metallurgical powder blend is consolidated by mechanically or isostatically compressing to form the green compact, typically at pressures between 10,000 and 60,000 psi. In certain cases, the green compact may be pre-sintered at a temperature between about 400° C. and 1200° C. to form a “brown” compact. The green or brown compact is subsequently sintered to autogenously bond together the metallurgical powder particles and further densify the compact. In certain embodiments the powder compact may be sintered in vacuum or in hydrogen. In certain embodiments the compact is over pressure sintered at 300-2000 psi and at a temperature of 1350-1500° C. Subsequent to sintering, the article may be appropriately machined to form the desired shape or other features of the particular geometry of the article.
Embodiments of the present disclosure include methods of making a composite sintered powder metal composite article. One such method includes placing a first metallurgical powder into a first region of a void of a mold, wherein the first powder includes hard particles and a powdered binder. A second metallurgical powder blend is placed into a second region of the void of the mold. The second powder may include at least one of a metal powder and a metal alloy powder selected from the group consisting of a steel powder, a nickel powder, a nickel alloy powder, a molybdenum powder, a molybdenum alloy powder, a titanium powder, a titanium alloy powder, a cobalt powder, a cobalt alloy powder, a tungsten powder, and a tungsten alloy powder. The second powder may contact the first powder, or initially may be separated from the first powder in the mold by a separating means. Depending on the number of cemented hard particle and metal or metal alloy regions desired in the composite article, the mold may be partitioned into additional regions in which additional metallurgical powder blends may be disposed. For example, the mold may be segregated into regions by placing one or more physical partitions in the void of the mold to define the several regions and/or by merely filling regions of the mold with different powders without providing partitions between adjacent powders. The metallurgical powders are chosen to achieve the desired properties of the corresponding regions of the article as described herein. The materials used in the embodiments of the methods of this disclosure may comprise any of the materials discussed herein, but in powdered form, such that they can be pressed and sintered. Once the powders are loaded into the mold, any partitions are removed and the powders within the mold are then consolidated to form a green compact. The powders may be consolidated, for example, by mechanical or isostatic compression. The green compact may then be sintered to provide a composite sintered powder metal article including a cemented hard particle region formed from the first powder and metallurgically bonded to a second region formed from the second metal or metallic alloy powder. For example, sintering may be performed at a temperature suitable to autogenously bond the powder particles and suitably densify the article, such as at temperatures up to 1500° C.
The conventional methods of preparing a sintered powder metal article may be used to provide sintered articles of various shapes and including various geometric features. Such conventional methods will be readily known to those having ordinary skill in the art. Those persons, after considering the present disclosure, may readily adapt the conventional methods to produce composites articles according to the present disclosure.
A further embodiment of a method according to the present disclosure comprises consolidating a first metallurgical powder in a mold forming a first green compact and placing the first green compact in a second mold, wherein the first green compact fills a portion of the second mold. The second mold may be at least partially filled with a second metallurgical powder. The second metallurgical powder and the first green compact may be consolidated to form a second green compact. Finally, the second green compact is sintered to further densify the compact and to form a metallurgical bond between the region of the first metallurgical powder and the region of the second metallurgical powder. If necessary, the first green compact may be presintered up to a temperature of about 1200° C. to provide additional strength to the first green compact. Such embodiments of methods according to the present disclosure provide increased flexibility in design of the different regions of the composite article, for particular applications. The first green compact may be designed in any desired shape from any desired powder metal material according to the embodiments herein. In addition, the process may be repeated as many times as desired, preferably prior to sintering. For example, after consolidating to form the second green compact, the second green compact may be placed in a third mold with a third metallurgical powder and consolidated to form a third green compact. By such a repetitive process, more complex shapes may be formed. Articles including multiple clearly defined regions of differing properties may be formed. For example, a composite article of the present disclosure may include cemented hard particle materials where increased wear resistance properties, for example, are desired, and a metal or metallic alloy in article regions at which it is desired to provide mechanical attachment features.
Certain embodiments of the methods according to the present disclosure are directed to composite sintered powder metal articles. As used herein, a composite article is an object that comprises at least two regions, each region composed of a different material. Composite sintered powder metal articles according to the present disclosure include at least a first region, which includes cemented hard particles, metallurgically bonded to a second region, which includes at least one of a metal and a metallic alloy. Two non-limiting examples of composite articles according to the present disclosure are shown in
In composite articles according to the present disclosure, the cemented hard particles of the first region are a composite including a discontinuous phase of hard particles dispersed in a continuous binder phase. The metal and/or metallic alloy included in the second region is one or more selected from a steel, nickel, a nickel alloy, titanium, a titanium alloy, molybdenum, a molybdenum alloy, cobalt, a cobalt alloy, tungsten, and a tungsten alloy. The two regions are formed from metallurgical powders that are pressed and sintered together. During sintering, a metallurgical bond forms between the first and second regions, for example, at the interface between the cemented hard particles in the first region and the metal or metallic alloy in the second region.
In the embodiments of the methods of the present disclosure, the present inventors determined that the metallurgical bond that forms between the first region (including cemented hard particles) and the second region (including at least one of a metal and a metallic alloy) during sintering is surprisingly and unexpectedly strong. In various embodiments produced according to the present disclosure, the metallurgical bond between the first and second regions is free from significant defects, including cracks. Such bond defects commonly are present when conventional techniques are used to bond a cemented hard particle material to a metal or metallic alloy. The metallurgical bond formed according to the present disclosure forms directly between the first and second regions at the microstructural level and is significantly stronger than bonds formed by prior art techniques used to bind together cemented carbides and metal or metallic alloys, such as the casting technique discussed in U.S. Pat. No. 5,359,772 to Carlsson, which is described above. The metallurgical bond formed by the press and sinter technique using the materials recited herein avoids the stresses and cracking experienced with other bonding techniques. This is believed to be at least partially a result of the nature of the strong metallurgical bond formed by the technique of the present disclosure, and also is a result of the compatibility of the materials used in the present technique. It has been discovered that not all metals and metallic alloys can be sintered to cemented hard particles such as cemented carbide. Also, the strong bond formed according to the present disclosure effectively counteracts stresses resulting from differences in thermal expansion properties of the bonded materials, such that no cracks form in the interface between the first and second regions of the composite articles.
In certain embodiments of the methods according to the present disclosure, the first region comprising cemented hard particles has a thickness greater than 100 microns. Also, in certain embodiments, the first region has a thickness greater than that of a coating.
The embodiments of the methods described herein achieve an unexpectedly and surprisingly strong metallurgical bond between the first region (including cemented hard particles) and the second region (including at least one of metal and a metallic alloy) of the composite article. In certain embodiments of the methods according to the present disclosure, the formation of the superior bond between the first and second regions is combined with the step of incorporating advantageous mechanical features, such as threads or keyways, on the second region of the composite to provide a strong and durable composite article that may be used in a variety of applications or adapted for connection to other articles for use in specialized applications.
In certain embodiments of the methods according to the present disclosure, the first and second regions each have a thickness greater than 100 microns. In certain other embodiments, each of the first and second regions has a thickness greater than 0.1 centimeters. In still other embodiments, the first and second regions each have a thickness greater than 0.5 centimeters. Certain other embodiments according to the present disclosure include first and second regions having a thickness of greater than 1 centimeter. Still other embodiments comprise first and second regions having a thickness greater than 5 centimeters. Also, in certain embodiments of the methods according to the present disclosure, at least the second region or another region of the composite sintered powder metal article has a thickness sufficient for the region to include mechanical attachment features such as, for example, threads or keyways, so that the composite article can be attached to another article via the mechanical attachment features.
In other embodiments according to the methods of the present disclosure, a metal or metallic alloy of the second region has a thermal conductivity less than a thermal conductivity of the cemented hard particle material of the first region, wherein both thermal conductivities are evaluated at room temperature (20° C.). Without being limited to any specific theory, it is believed that the metal or metallic alloy of the second region must have a thermal conductivity that is less than a thermal conductivity of the cemented hard particle material of the first region in order to form a metallurgical bond between the first and second regions having sufficient strength for certain demanding applications of cemented hard particle materials. In certain embodiments, only metals or metallic alloys having thermal conductivity less than a cemented carbide may be used in the second region. In certain embodiments, the second region or any metal or metallic alloy of the second region has a thermal conductivity less than 100 W/mK. In other embodiments, the second region or any metal or metallic alloy of the second region may have a thermal conductivity less than 90 W/mK.
In certain other embodiments of the methods according to the present disclosure, the metal or metallic alloy of the second region of the composite article has a melting point greater than 1200° C. Without being limited to any specific theory, it is believed that the metal or metallic alloy of the second region must have a melting point greater than 1200° C. so as to form a metallurgical bond with the cemented hard particle material of the first region with bond strength sufficient for certain demanding applications of cemented hard particle materials. In other embodiments, the metal or metallic alloy of the second region of the composite article has a melting point greater than 1275° C. In some embodiments, the melting point of the metal or metallic alloy of the second region is greater than a cast iron.
According to the present disclosure, the cemented hard particle material included in the first region must include at least 60 percent by volume dispersed hard particles. If the cemented hard particle material includes less than 60 percent by volume of hard particles, the cemented hard particle material will lack the required combination of abrasion and wear resistance, strength, and fracture toughness needed for applications in which cemented hard particle materials are used. Accordingly, as used herein, “cemented hard particles” and “cemented hard particle material” refer to a composite material comprising a discontinuous phase of hard particles dispersed in a continuous binder material, and wherein the composite material includes at least 60 volume percent of the hard particle discontinuous phase.
In certain embodiments of the methods of making the composite articles according to the present disclosure, the metal or metallic alloy of the second region may include from 0 up to 50 volume percent of hard particles (based on the volume of the metal or metallic alloy). The presence of certain concentrations of such particles in the metal or metallic alloy may enhance wear resistance of the metal or alloy relative to the same material lacking such hard particles, but without significantly adversely affecting machineability of the metal or metallic alloy. Obviously, the presence of up to 50 volume percent of such particles in the metallic alloy does not result in a cemented hard particle material, as defined herein, for at least the reason that the hard particle volume fraction is significantly less than in a cemented hard particle material. In addition, it has been discovered that in certain composite articles according to the present disclosure, the presence of hard particles in the metal or metallic alloy of the second region may modify the shrinkage characteristics of the region so as to more closely approximate the shrinkage characteristics of the first region. In this way, the CTE of the second region may be adjusted to better ensure compatibility with the CTE of the first region to prevent formation of stresses in the metallurgical bond region that could result in cracking.
Thus, in certain embodiments of the methods according to the present disclosure, the metal or metallic alloy of the second region of the composite article includes from 0 up to 50 percent by volume, and preferably no more than 20 to 30 percent by volume, hard particles dispersed in the metal or metallic alloy. The minimum amount of hard particles in the metal or metallic alloy region that would affect the wear resistance and/or shrinkage properties of the metal or metallic alloy is believed to be about 2 to 5 percent by volume. Thus, in certain embodiments according to the present disclosure, the metallic alloy of the second region of the composite article includes from 2 to 50 percent by volume, and preferably from 2 to 30 percent by volume hard particles dispersed in the metal or metallic alloy. Other embodiments may include from 5 to 50 percent hard particles, or from 5 to 30 percent by volume hard particles dispersed in the metal or metallic alloy. Still other embodiments may comprise from 2 to 20, or from 5 to 20 percent by volume hard particles dispersed in the metal or metallic alloy. Certain other embodiments may comprise from 20 to 30 percent by volume hard particles dispersed in the metal or metallic alloy.
The hard particles included in the first region and, optionally, the second region may be selected from, for example, the group consisting of a carbide, a nitride, a boride, a silicide, an oxide, and mixtures and solid solutions thereof. In one embodiment, the metal or metallic alloy of the second region includes up to 50 percent by volume of dispersed tungsten carbide particles.
In certain embodiments of the methods according to the present disclosure, the dispersed hard particle phase of the cemented hard particle material of the first region may include one or more hard particles selected from a carbide, a nitride, a boride, a silicide, an oxide, and solid solutions thereof. In certain embodiments, the hard particles may include carbide particles of at least one transition metal selected from titanium, chromium, vanadium, zirconium, hafnium, tantalum, molybdenum, niobium, and tungsten. In still other embodiments, the continuous binder phase of the cemented hard particle material of the first region includes at least one of cobalt, a cobalt alloy, nickel, a nickel alloy, iron, and an iron alloy. The binder also may include, for example, one or more elements selected from tungsten, chromium, titanium, tantalum, vanadium, molybdenum, niobium, zirconium, hafnium, and carbon, up to the solubility limits of these elements in the binder. Additionally, the binder may include up to 5 weight percent of one of more elements selected from copper, manganese, silver, aluminum, and ruthenium. One skilled in the art will recognize that any or all of the constituents of the cemented hard particle material may be introduced into the metallurgical powder from which the cemented hard particle material is formed in elemental form, as compounds, and/or as master alloys.
The properties of cemented hard particle materials, such as cemented carbides, depend on parameters including the average hard particle grain size and the weight fraction or volume fraction of the hard particles and/or binder. In general, the hardness and wear resistance increases as the grain size decreases and/or the binder content decreases. On the other hand, fracture toughness increases as the grain size increases and/or the binder content increases. Thus, there is a trade-off between wear resistance and fracture toughness when selecting a cemented hard particle material grade for any application. As wear resistance increases, fracture toughness typically decreases, and vice versa.
Certain other embodiments of the methods to make the articles of the present disclosure include hard particles comprising carbide particles of at least one transition metal selected from titanium, chromium, vanadium, zirconium, hafnium, tantalum, molybdenum, niobium, and tungsten. In certain other embodiments, the hard particles include tungsten carbide particles. In still other embodiments, the tungsten carbide particles may have an average grain size of from 0.3 to 10 μm.
The hard particles of the cemented hard particle material in the first region preferably comprise from about 60 to about 98 volume percent of the total volume of the cemented hard particle material. The hard particles are dispersed within a matrix of a binder that preferably constitutes from about 2 to about 40 volume percent of the total volume of the cemented hard particle material.
Embodiments of the methods to make the composite articles according to the present disclosure may also include hybrid cemented carbides such as, for example, any of the hybrid cemented carbides described in copending U.S. patent application Ser. No. 10/735,379, the entire disclosure of which is hereby incorporated herein by reference. For example, an article according to the present disclosure may comprise at least a first region including hybrid cemented carbide metallurgically bonded to a second region comprising one of a metal and a metallic alloy. Certain other articles may comprise at least a first region including cemented hard particles, a second region including at least one of a metal and a metallic alloy, and a third region including a hybrid cemented carbide material, wherein the first and third regions are metallurgically bonded to the second region.
Generally, a hybrid cemented carbide is a material comprising particles of at least one cemented carbide grade dispersed throughout a second cemented carbide continuous phase, thereby forming a microscopic composite of cemented carbides. The hybrid cemented of application Ser. No. 10/735,379 have low dispersed phase particle contiguity ratios and improved properties relative to certain other hybrid cemented carbides. Preferably, the contiguity ratio of the dispersed phase of a hybrid cemented carbide included in embodiments according to the present disclosure is less than or equal to 0.48. Also, a hybrid cemented carbide included in the embodiments according to the present disclosure preferably comprises a dispersed phase having a hardness greater than a hardness of the continuous phase of the hybrid cemented carbide. For example, in certain embodiments of hybrid cemented carbides included in one or more regions of the composite articles according to the present disclosure, the hardness of the dispersed phase in the hybrid cemented carbide is preferably greater than or equal to 88 Rockwell A Hardness (HRA) and less than or equal to 95 HRA, and the hardness of the continuous phase in the hybrid carbide is greater than or equal to 78 HRA and less than or equal to 91 HRA.
Additional embodiments of the methods to make the articles according to the present disclosure may include hybrid cemented carbide in one or more regions of the articles wherein a volume fraction of the dispersed cemented carbide phase is less than 50 volume percent of the hybrid cemented carbide, and wherein the contiguity ratio of the dispersed cemented carbide phase is less than or equal to 1.5 times the volume fraction of the dispersed cemented carbide phase in the hybrid cemented carbide.
Certain embodiments of the methods to make the articles according to the present disclosure include forming a mechanical attachment feature or other mechanical feature on at least the second region comprising at least one of a metal and a metallic alloy. A mechanical attachment feature, as used herein, enables certain articles according to the present disclosure to be connected to certain other articles and function as part of a larger device. Mechanical attachment features may include, for example, threads, slots, keyways, teeth or cogs, steps, bevels, bores, pins, and arms. It has not previously been possible to successfully include such mechanical attachment features on articles formed solely from cemented hard particles for certain demanding applications because of the limited tensile strength and notch sensitivity of cemented hard particle materials. Prior art articles have included a metal or metallic alloy region including one or more mechanical attachment features that were attached by means other than co-pressing and sintering to a cemented hard particle region. Such prior art articles suffered from a relatively weak bond between the metal or metallic alloy region and the cemented hard particle region, severely limiting the possible applications of the articles.
A composite article consisting of a cemented carbide portion and a tungsten alloy portion was fabricated according to the present disclosure using the following method. A layer of cemented carbide powder (FL30™ powder) was disposed in a mold in contact with a layer of tungsten alloy powder (consisting of 70% tungsten, 24% nickel, and 6% copper) and co-pressed to form a single composite green compact consisting of two distinct layers of consolidated powders. The pressing (or consolidation) was performed in a 100 ton hydraulic press employing a pressing pressure of approximately 20,000 psi. The green compact was a cylinder approximately 1.5 inches in diameter and approximately 2 inches long. The cemented carbide layer was approximately 1.0 inches long and the tungsten alloy layer was also approximately 1.0 inches long. Following pressing, the composite compact was sintered at 1400° C. in hydrogen, which minimizes or eliminates oxidation when sintering tungsten alloys. During sintering, the compact's linear shrinkage was approximately 18% along any direction.
Although the foregoing description has necessarily presented only a limited number of embodiments, those of ordinary skill in the relevant art will appreciate that various changes in the subject matter and other details of the examples that have been described and illustrated herein may be made by those skilled in the art, and all such modifications will remain within the principle and scope of the present disclosure as expressed herein and in the appended claims. For example, although the present disclosure has necessarily only presented a limited number of embodiments of rotary burrs constructed according to the present disclosure, it will be understood that the present disclosure and associated claims are not so limited. Those having ordinary skill will readily identify additional rotary burr designs and may design and build additional rotary burrs along the lines and within the spirit of the necessarily limited number of embodiments discussed herein. It is understood, therefore, that the present invention is not limited to the particular embodiments disclosed or incorporated herein, but is intended to cover modifications that are within the principle and scope of the invention, as defined by the claims. It will also be appreciated by those skilled in the art that changes could be made to the embodiments above without departing from the broad inventive concept thereof.
The present application claims priority under 35 U.S.C. §119(e) to co-pending U.S. Provisional Patent Application Ser. No. 61/057,885, filed Jun. 2, 2008.
| Number | Date | Country | |
|---|---|---|---|
| 61057885 | Jun 2008 | US |
