Impact of rare earth elements on nanohardness and nanowear properties of beta-type Ti-24Nb-38Zr-2Mo alloy for medical applications

This study investigated the impact of minor additions (0.10 wt.%) of rare earth elements scandium (Sc) and yttrium (Y) on nanohardness (H), reduced Young's modulus (E-r) and nanowear properties of a Ti-24Nb-38Zr-2Mo (TNZM) biomedical alloy. It found solid solution of Sc and Y in TNZM increased H and reduced E-r, but it's unclear if the E-r reduction of TNZMY was caused by Y solute, oxygen scavenging or synergistic effects thereof. Sc also improved wear resistance of TNZM by inhibiting wear formation and increasing plastic shear resistance. Sc increased the coefficient of friction (COF) of TNZM, while Y showed insignificant influence on COF. Determining the role of submicron Sc and micron Y-rich oxides on H, E-r and nanowear properties of TNZM was unsuccessful, but a low volume fraction of Sc oxides implied Y's affinity to oxygen > Sc's affinity to oxygen approximate to matrix phase's affinity to oxygen. Sc is highlighted as improving H and wear resistance, and reducing E-r of TNZM; Y is less recommended.