Effects of processing on microstructure and properties of Ti-Ta Alloys

Abstract

Titanium-Tantalum shape memory materials have widespread potential in biomedical applications due to their high degree of biocompatibility, favorable mechanical properties, high corrosion resistance and the possibility of exhibiting shape memory behavior 5' 6, 9. However, this system faces difficulties in processing due to the slow diffusion of Ta, with a melting point of 3269 K, and the sensitivity of shape memory materials on composition and processing history 8' 9 Dynamet Technology, Inc. has engineered a process in which these difficulties are overcome via powder metallurgy techniques, and the objective of this work was to characterize and explore the relationship between Dynamet's processing steps and the microstructure and properties of the Ti - 30 wt % Ta systems . Energy-dispersive x-ray analysis was used to quantify compositional gradients to verify homogeneity. Room temperature and high temperature x-ray diffractometry was used to identify phases present at temperatures ranging from room temperature up to 750 [degree]C. Hot extrusion without further heat treatment was found to be insufficient to produce a homogenous, fully dense alloy. Elongation, an indicator of potential shape memory behavior, was shown to increase with increased martensite phase fraction, which is thought to be dependent on cooling rate from above the austenite phase transformation starting temperature, Af. Finally, a phase transformation, likely that of martensite into beta-Ti, was verified to exist between 400 - 600 [degree]C.