Evaluations of microstructure and fatigue properties of Ti-Ta alloys

Abstract

In recent years, the demand for implants has increased in the orthopedic field due to the aging of the population. Among them, Ti-6Al-4V alloy is very often used. However, its high Young's modulus and cytotoxicity are regarded as problems. Therefore, we are focusing on titanium and tantalum, which are highly corrosion-resistant elements, and are developing Ti-Ta alloy, which is a β-type titanium alloy that exhibits low Young's modulus and low cytotoxicity. Furthermore, from the viewpoint of safety and durability, both high strength and low elasticity and excellent fatigue characteristics are required. In this study, we identified the microstructure and crystal structure of 4-types of heat-treated Ti-Ta alloys. In addition, torsional fatigue and plane bending fatigue tests were performed. By comparing these results, we investigated the relationship between structure and fatigue characteristics. From SEM and TEM observation, EBSD and EDS results, it was found that Tantaulum was dissolved in the β-Ti matrix in any heat treatment conditions. Furthermore, α-Ti was deposited at the grain boundaries by 500℃ aging. It was also found that the average crystal grain size increased due to the increase in the solution temperature and the aging treatment. Then, the torsional fatigue characteristics improved as the crystal grain size became smaller. The plane bending fatigue characteristics were improved by strengthening precipitation with α-Ti.