Homogeneous titanium tungsten alloys produced by powder metal technology

Abstract

The present disclosure is related to homogeneous alloys comprising titanium and 9% to less than 20% by weight of tungsten, wherein the alloy has a yield strength of at least 120,000 psi and ductility of least 20% elongation; and with further alloying an ultimate tensile strength of at least 200,000 psi and useful ductility of at least 2% elongation; and with the addition of ceramic particulate reinforcements can exhibit an ultimate tensile strength of at least 180,000 psi. Products and metal matrix composites comprising such homogeneous alloys are also disclosed. The metal matrix composites further comprise a discontinuous reinforcement chosen from TiC, TiB2, or TiB, particles or combinations of such particles. Method of making such alloys and composites as well as products made from such alloys and composites are also disclosed.

Description

[0001] This application claims the benefit of priority to provisional application 60 / 772,896, filed Feb. 14, 2006, which is herein incorporated by reference in its entirety.[0002] Disclosed herein are homogeneous titanium-tungsten alloys and metal matrix composites having highly desirable properties. Also disclosed are methods of making such alloys and composites, as well as products comprising such alloys and composites. [0003] Titanium metal has typically been alloyed with other metallic elements to increase the tensile strength over the pure metal. Early commercial titanium alloying elements Fe, Mn, and Cr improved strength but drastically lowered the ductility. Good ductility is desired in the typical component both to be formable (malleable) enough to produce the final shape by metalworking and to possess sufficient fracture resistance to deformation for use in the end-use application. [0004] With the development of the Ti-6Al-4V alloy (U.S. Pat. No. 2,906,654), which is herein...

AI Technical Summary

Benefits of technology

[0005] For many metal working processes such as sheet bending, cold drawing and the manufacture of foil and thin wall tubing (e.g. aircraft hydraulic tubing), even Ti-6Al-4V becomes difficult to fabricate. In this case, commercially pure (CP) titanium a low alloyed titanium (Ti-3Al-2.5V) or an extra low interstitial (ELI) grade of Ti-6Al-4V is employed. In this way the ductility is improved but at a significant sacrifice of strength.

[0006] The most ductile titanium is unalloyed commercially pure titanium. The most commonly used unalloyed grade titanium is CP titanium Grade 2. This grade is widely employed for components requiring significant deformation in fabrication. CP Grade 2 has a typical tensile strength of 67,000 psi and a yield strength of 47,000 psi with a tensile ductility of 26% elongation. This high ductility permits the material to undergo severe deformation during fabrication, unlike the higher strength alloys such as Ti-6Al-4V (at 10-14% elongation) that lack the necessary malleability. A high strength titanium alloy possessing the high ductility of commercially pure titanium has long been desired to enhance the manufacturing technology of titanium components.

[0010] The present disclosure describes a method of making a heat treatable titanium base alloy that possesses combinations of properties that make them highly desirable. For example, in one embodiment of the invention there is described an alloy comprising titanium and 9 to less than 20% by weight of tungsten, wherein the alloy exhibits a yield strength of at least 120,000 psi and a ductility of at least 20% elongation. Applications for these highly ductile alloys include those in which the combination of high strength with high ductility is desired. For example, these materials are advantageous for medical and dental (orthopaedic implants, stents, etc.), automotive (valves, connecting rods, spring retainers, etc.), industrial (fittings, pumps, fasteners, etc.), military (ballistic armor, ordnance components, etc.) and other applications where the combination of high strength with high ductility permits readily fabrication of high strength components.

Problems solved by technology

Early commercial titanium alloying elements Fe, Mn, and Cr improved strength but drastically lowered the ductility.

Although several later alloys were developed, such alloys achieved only incremental improvements in specific properties such as higher elevated strength, better weldability or improved fatigue strength.

For many metal working processes such as sheet bending, cold drawing and the manufacture of foil and thin wall tubing (e.g. aircraft hydraulic tubing), even Ti-6Al-4V becomes difficult to fabricate.

In this way the ductility is improved but at a significant sacrifice of strength.

However this heavy metal element caused severe segregation problems when incorporated in the ingot melting technology of the industry.

The large difference in density between tungsten (19.3 g / cm3) and titanium (4.51 g / cm3) and the disparity between the melting points of tungsten (above 3400° C.) and titanium (below 1700° C.) results in gross inhomogeneity of the alloy composition and tungsten and likely accounts for its lack of commercialization as an alloy ingredient for titanium.

To the extent that titanium alloys containing tungsten can be produced, the processes needed to achieve a homogenous alloy requires multiple melting steps and are thus very uneconomical.

It is very difficult to produce homogenous Ti alloys containing W. W is a highly refractory metal that has a much higher melting point than that of Ti.