FIGURE 1: Optical micrograph of Ti-10 wt.% W etched with modified Kroll’s agent (5% nitric acid; 10% hydrofluoric acid, balance water).
One of the most promising application groups for titanium and its alloys is in the field of biomaterials, and specifically orthopedic biomaterials. Titanium alloys are desirable in these applications because of their high biocompatibility and corrosion resistance, high strength, relatively low modulus (which helps alleviate stress shielding arising from differences in compliance between biomaterials and host tissue) and density, and lack of magnetism. The latter property is important in orthopedic biomaterials because of heavy clinical reliance on magnetic resonance imaging (MRI), a magnetic resonance technique used to map physiological responses to implanted biomaterials. Another commonly used biomaterial class, the Co-based superalloys, shows magnetic properties which cause heavy distortion to MRI images, complicating post-surgical and long-term treatments.
Another major requirement for orthopedic biomaterials is resistance to wear, as wear debris can cause severe inflammatory responses in surrounding tissue as well as other undesirable host reactions. Unfortunately, the wear resistance of unalloyed Ti is considered poor by biomedical standards, and typical alloying additions (e.g., Al, V, Fe, Mo, Nb) may have adverse biological effects. Consequently there is some need for the development of alternative alloying additions for Ti-based orthopedic biomaterials. Ti/W alloys offer a promising solution to this need for a number of reasons. Firstly, in low concentrations the presence of W would not be expected to significantly increase corrosion rates or material density, while still providing high gains in overall strength. The addition of small amounts of W has also been shown to decrease the elastic modulus of Ti, improving stress-shielding properties. In addition, W is nonmagnetic and highly radio-opaque, allowing more effective use of MRI and radiographical techniques for monitoring implant response. Most importantly, however, the fact that W is soluble in Ti at accessible temperatures, and insoluble at ambient temperature, allows the development of heat treatments designed to optimize W distribution for greatly improved hardness and wear resistance.
The focus of the present work is to investigate the conditions under which such heat treatments must be performed for optimal hardness. We also investigate tensile and fatigue properties of various Ti-TiC-W alloy systems at ambient temperatures in conjunction with the heat treatments.
Related Publications
- M. Frary, S. Abkowitz, S.M. Abkowitz, D.C. Dunand. “Microstructural and Mechanical Properties of Ti/W and Ti-6Al-4V/W Composites Fabricated by Powder Metallurgy”, Materials Science and Engineering A, 344, 1-2, 103-112 (2003).
PDF
Financial Support
This research is funded by the National Institutes of Health trough a SBIR subcontract from Dynamet Technology, Inc.
