Patent Application
20140079583
Disclosed herein are titanium-tungsten alloys and composites. Also disclosed is a method of making such alloys and composites using nanopowders of tungsten and optionally comprising slow-diffusing beta stabilizers, such as but not limited to V, Nb, Mo, and Ta.
While Ti alloys strengthened by W are generally desirable because they are strong wear resistant alloys, such alloys are difficult, if not impossible, to prepare by typical techniques. For example, in a casting process, W generally completely dissolves in the molten Ti during the melting step. As the resulting ingot solidifies beta-rich large, elongated islands form between the dendrites of the solidified casting. These resulting defects lead to poor mechanical properties in the final product.
Until the present disclosure, the preparation of Ti—W by powder metallurgy (PIM), was not commercially viable because of the high melting point and slow diffusivity associated with W that causes it to remain segregated as discrete or undissolved particles. Ti—W alloys are mentioned in the literature for use as sputtering targets and in thin film applications; however, these alloys are tungsten (W) based with typically 10% or less Ti.
Literature that does describe Ti based alloys comprising W describes W being added to form a particulate dispersion. For example, M. Frary, S. M. Abkowitz, and D. C. Dunand, “Microstructure and Mechanical Properties of Ti/W and Ti-6Al-4V/W Composites Fabricated by Powder-Metallurgy,” Materials Science and Engineering A344 (2003) 103-112, which is herein incorporated by reference, shows that partially diffused W dispersions in Ti powder (Commercially Pure “CP” Ti) and Ti-based alloys (Ti-6Al-4V) increases strength with an acceptable loss in ductility. The alloys described in Frary et al. comprise 3 μm to 10 μm tungsten powders that are too large to completely diffuse.
The present disclosure avoids the aforementioned problems by using tungsten nanopowder. As used herein, nanopowder is defined as powders less than 1 micron, such as powders ranging from about 8 angstroms (the detection limit of electron microscopy) to less than 1 micron. The Inventors have discovered that the use of W nanopowder in the preparation of Ti—W alloys allows the W to completely diffuse into the Ti matrix during a typical P/M sintering cycle.
In one embodiment, completely diffused W nanopowder forms an alpha/beta or all beta microstructure, or as alpha/beta or all beta microstructure containing a dispersion described as “beta phase islands.” Beta phase islands are a microscopic beta rich structure dispersed throughout an alpha, alpha/beta or all-beta microstructure. These dispersions result in Ti/W alloys with properties that are superior to a dispersion of partially diffused W particulates produced using Ti powder 3 μm or larger. In fact, the commercially pure (CP) Ti with 10% W containing dispersions of beta phase islands can have properties superior to Ti-6Al-4V. In addition, the Ti-6Al-4V with 10% W can have annealed properties equivalent to the highly alloyed all-beta alloys that require solution treatment and aging to fully develop their properties (e.g. Ti-13V-11Cr-3Al).
In accordance with the present disclosure, W nanopowder can be blended with CP (commercially pure) Ti powder and, in the case of an alloy, blended with Ti powder, other elemental powders or with master alloy powders, which is defined as the mixture of starting metal powders used to form the resulting alloy by powder metallurgy processing. The powder blend is compacted, sintered and may or may not be hot isostatic pressed. The product may be subjected to additional processing, such as, forging, casting, or extrusion.
A casting billet may also be prepared in the manner described above and then cast to shape. Ti—W master alloy additions can also be prepared by the methods disclosed in this invention. These master alloy additions can be used in casting of Ti—W or may be made into master alloy powder by attrition for use in P/M processing.
The total diffusion of W, as disclosed herein, results in an alpha/beta phase microstructure in CP titanium typical of commercial alpha/beta alloys. In alpha/beta alloys the total diffusion of W results in a near beta or all beta microstructure. The Ti—W alloys also have properties that are superior to conventional Ti-6Al-4V. Further the Ti—W alpha/beta and all-beta alloys can be solution treated and aged in much the same way as conventional heat treatable Ti alloys.
Disclosed herein is a method of making an alloy having a uniform dispersion of beta phase islands within a Ti matrix. According to this aspect, this uniform dispersion of beta phase islands can be controlled within the Ti matrix by adjusting the P/M sintering time and/or by manipulating the W powder size to a range from 8 angstroms to less then 3 μm, such as less than 1 μm. The beta phase island dispersion results in improved room and elevated temperature properties.
In another aspect of the disclosure, the above-described method based on tungsten (W) can be used with other beta stabilizers, such as but not limited to V, Nb, Mo, and Ta. In this embodiment, the powder size of the particular beta stabilizer is related to the beta stabilizer's diffusivity at the sintering temperature of Ti.
The creation of a uniform dispersion of beta phase is dependent on, among other things, the size of the beta stabilizer powder. In one embodiment, the beta stabilizer powder is less then 3 μm, such as less than 1 μm. The powder size used according to the present disclosure is also related to the beta stabilizer's diffusivity at the sintering temperature. In addition, the powder size range can depend on the desired matrix microstructure (i.e. alpha/beta or all beta), the size and number of beta phase islands and the desired amount of partially diffused beta stabilizer (residual undiffused particulate) with the beta phase islands, such as at the center of the beta phase islands.
Partially dissolved particles of the beta-stabilizing addition, such as partially dissolved particles of W, V, Nb, Mo, or Ta, may be present within, such as at the center of, the beta phase islands and may contribute to the strengthening mechanism.
The properties of Ti metal matrix composites containing particulate reinforcement of titanium carbide (TiC), titanium boride (TiB) or titanium diboride (TiB2) can also be enhanced by W nanopowder additions or the addition of sub-sieve sized powder of other beta stabilizers.
The accompanying micrograph that is incorporated in and constitutes a part of this specification, illustrates one embodiment of the invention and together with the description, serve to explain the principles of the disclosure.
One aspect of the present disclosure is directed to a composition of a titanium based alloy comprising a titanium material and tungsten in an amount ranging from 0.5% to 40% by weight. In one embodiment, the W powder addition used to make the alloy has an average diameter of less then 3 μm in size, such as less than 1 μm, and ranging from 8 angstroms to less then 1 μm as measured by the Fisher sub-screen size method, electron microscopy and/or photon correlation spectroscopy.
The titanium in the Ti/W alloy described herein may comprise CP Ti powder or a Ti alloy, such as Ti-6Al-4V.
The composition may comprise an alternative or additional slow diffusing beta stabilizer chosen from but not limited to V, Nb, Mo, and Ta. Such stabilizers will lead to an alloy containing dispersions of beta phase islands or an all beta structure with dispersions of partially dissolved beta stabilizer. In one embodiment, the beta phase islands contain undiffused particulate beta stabilizer at the core of the islands.
As described in the prior art, “beta flecks”, are generally a form of beta phase islands that are well-known as a defect. See, for example, “Powder Metallurgy of Titanium Alloys,” by Froes and Smugeresky, The Metallurgical Society of AIME, Warrendale, Pa. 1980; ASM Online Handbook, “Wrought Titanium and Titanium Alloys—Wrought Titanium Processing,”; “Processing of Titanium and Titanium Alloys—Secondary Fabrication,” Y. G. Zhou, J. L. Tang, H. Q. Yu, and W. D. Zeng, “Effects of Beta Fleck on the Properties of Ti-10V-2Fe-3Al Alloy,” Titanium 1992 Science and Technology, The Minerals, Metals and Materials Society, Warrendale, Pa. 1992, Vol 1, pp513-521; and http://mse-p012.eng.ohio-state.edu/fraser/mse663/AlphaBeta JCW.pdf, “Properties and Applications of α+β Ti Alloys, which are all incorporated herein by reference.
The occurrence of beta fleck defects is generally unpredictable, and usually results in poor properties, and thus may lead to the premature failure of a component. Contrary to the teachings of the prior art, the present disclosure provides for the creation of uniform dispersions of beta phase islands that can improve the mechanical properties of Ti and its alloys. The beta fleck defect occurs in alpha-beta and near beta alloys where segregation of alloying elements results in localized regions depleted in alpha stabilizers (e.g. aluminum) or with an excess of beta stabilizers (e.g. molybdenum). These regions then transform to the beta phase resulting in beta flecks. Contamination of powder or castings by tramp particles of a beta stabilizer, such as W, can also result in beta flecks.
The present disclosure teaches that controlled dispersions of the so-called “beta fleck”, herein termed “beta phase islands”, can be beneficial and improve the properties of titanium and its alloys.
In another embodiment, the alloy has a microstructure that comprises all-alpha phase, alpha/beta phases and all beta phase, or all-alpha phase and alpha/beta phases comprising a dispersion of beta phase islands. The beta phase islands optionally include partially diffused beta stabilizer within the beta phase islands, such as at the center of the beta phase islands.
Also described herein is a powder metallurgical method of making the above-described composition. This method comprises:
After powder metallurgical processing as described above the part may be further processed by techniques including, but not limited to casting, forging, and extrusion.
In one embodiment, the alloy described herein may be used in implantable medical devices, such as orthopedic implants, including spinal implants, disc prostheses, nucleus prostheses, bone fixation devices, bone plates, spinal rods, rod connectors, knees, and hip prostheses, dental implants, implantable tubes, wires, and electrical leads. In other embodiments, the alloy may be used in drug delivery devices, including stents.
The alloy disclosed herein may also be formed into a product, such as a billet for further processing. In other embodiment, the product may be an automotive component such as valves, conrods, and piston pins.
The product may also comprise an armored vehicle component such as tank track center guides and undercarriage parts.
In another embodiment, the product may comprise a tool or die material for metal casting.
The product may also be an aircraft component such as a turbine rotor, and a leading edge of a helicopter rotor blade.
All amounts, percentages, and ranges expressed herein are approximate.
The present invention is further illuminated by the following non-limiting example, which is intended to be purely exemplary of the invention.
A powder metallurgy technique was used to produce a tungsten containing titanium alloy. Using this method, beta phase island dispersions were created in CP Ti and in Ti-6Al-4V with 10% by weight W. In this example, nanopowder 30 to 45 nanometers (0.003 to 0.004 μm) in size with a specific surface area of between 7 to 10 m2/g was blended with CP Ti powder and processed as described above. These W nanopowders were also blended with CP Ti and master alloy powders to form the Ti-6Al-4V composition shown in Table 1.
The W nanopowder was taken into solution in the Ti matrix on sintering the compacted blend, forming an alpha/beta structure with a uniform beta phase island dispersion.
Table 1 shows that 10% W nano-sized powder addition substantially improved the strength of CP Ti resulting in twice the strength of CP Ti, as well as a higher strength then Ti-6Al-4V with roughly equivalent ductility. In the Ti-6Al-4V containing composition, the W nanopowder addition resulted in a 30% improvement in strength while maintaining satisfactory ductility.
Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.
This application claims the benefit of domestic priority to U.S. Provisional Patent Application Ser. No. 60/563,009, filed Apr. 19, 2004, which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60563009 | Apr 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11108865 | Apr 2005 | US |
| Child | 13850488 | US |
