Wear transition of solid-solution-strengthened Ti-29Nb-13Ta-4.6Zr alloys by interstitial oxygen for biomedical applications

In previous studies, it has been concluded that volume losses (V_loss) of the Ti-29Nb-13Ta-4.6Zr (TNTZ) discs and balls are larger than those of the respective Ti-6Al-4V extra-low interstitial (Ti64) discs and balls, both in air and Ringer[U+05F3]s solution. These results are related to severe subsurface deformation of TNTZ, which is caused by the lower resistance to plastic shearing of TNTZ than that of Ti64. Therefore, it is necessary to further increase the wear resistance of TNTZ to satisfy the requirements as a biomedical implant. From this viewpoint, interstitial oxygen was added to TNTZ to improve the plastic shear resistance via solid-solution strengthening. Thus, the wear behaviors of combinations comprised of a new titanium alloy, TNTZ with high oxygen content of 0.89mass% (89O) and a conventional titanium alloy, Ti64 were investigated in air and Ringer[U+05F3]s solution for biomedical implant applications. The worn surfaces, wear debris, and subsurface damage were analyzed using a scanning electron microscopy and an electron probe microanalysis. V_loss of the 89O discs and balls are smaller than those of the respective TNTZ discs and balls in both air and Ringer[U+05F3]s solution. It can be concluded that the solid-solution strengthening by oxygen effectively improves the wear resistance for TNTZ materials. However, the 89O disc/ball combination still exhibits higher V_loss than the Ti64 disc/ball combination in both air and Ringer[U+05F3]s solution. Moreover, V_loss of the disc for the 89O disc/Ti64 ball combination significantly decreases in Ringer[U+05F3]s solution compared to that in air. This decrease for the 89O disc/Ti64 ball combination in Ringer[U+05F3]s solution can be explained by the transition in the wear mechanism from severe delamination wear to abrasive wear.