Formation of a hydroxyapatite layer on Ti–29Nb–13Ta–4.6Zr and enhancement of four-point bending fatigue characteristics by fine particle peening

Abstract

A hydroxyapatite (HAp) surface layer was generated at room temperature on a beta-titanium alloy (Ti-29Nb-13Ta-4.6Zr, TNTZ) using fine particle peening (FPP), as a means of enhancing fatigue resistance. This material is commonly employed in bio-implants, but has a suboptimal Young's modulus. Treated specimens were assessed using scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy and electron backscatter diffraction, as well as by measuring the Vickers hardness. Performing FPP using shot particles made of HAp was found to transfer the particles to the TNTZ surface to rapidly produce a HAp layer that became thicker as the FPP process progressed. Room-temperature four-point bending fatigue tests in air showed that the HAp layer resulting from the FPP process increased the endurance limit of test specimens. This improved performance is ascribed to the appearance of a hardened surface layer having a significant degree of compressive residual stress.