Fatigue characteristics of low cost β titanium alloys for healthcare and medical applications

Two new low cost beta titanium alloys, Ti-4.317e-7.1 Cr (TFC alloy) and Ti-43Fe-7. 1Cr-3.0Al (TFCA alloy) for healthcare and medical applications have been recently developed. As for such applications, the alloys are necessary to have high fatigue performance. The aim of this study is, therefore, to investigate fatigue characteristics of the alloys subjected to solution treatment above beta transus. Fatigue tests were carried out at a stress ratio, R, of 0.1 and a frequency of 10 Hz. Fatigue limit of the solution treated TFC alloy is higher than that of the solution treated TFCA alloy, but both are higher than that of the existing biometallic materials. Fatigue strength of the TFC alloy is almost independent of solution treatment temperature, while, fatigue strength of the TFCA alloy strongly depends on solution treatment temperature, especially, in the low cycle fatigue life (LCF) region. The fatigue ratio and biofunctionality of these new alloys are much higher than those of the existing biometallic materials. In general, a crack initiates from the surface in the LCF region and from subsurface (internal) in the high cycle fatigue life (HCF) region for the TFC alloy, while, in the case of the TFCA alloy, a crack tends to initiate from the subsurface in both LCF and HCF regions. The internal crack initiation sites are found to be the area with low beta phase stability in the LCF region and at the area with high stability of P phase in the HCF region. The relatively low fatigue strength of TFCA alloy is associated with the addition of Al that leads to precipitate et phase in which both crack initiation and facet formation are easier to occur.