Effect of Fine Particle Peening Using Hydroxyapatite Particles on Rotating Bending Fatigue Properties of β-Type Titanium Alloy

Yuki Nakamura,Toshikazu Akahori,Shoichi Kikuchi,Koichiro Nambu,Toshihiro Shimizu

doi:10.3390/app11094307

Abstract

Fine particle peening (FPP) using hydroxyapatite (HAp) shot particles was performed to improve the fatigue strength and form a HAp transfer layer on a beta titanium alloy (Ti–22V–4Al). The surface microstructures of the FPP-treated specimen were characterized using scanning electron microscopy, micro-Vickers hardness testing, energy dispersive X-ray spectrometry, X-ray diffraction, and electron backscattered diffraction. A HAp transfer layer with a thickness of 5.5 μm was formed on the surface of the Ti–22V–4Al specimen by FPP. In addition, the surface hardness of the Ti–22V–4Al was increased, and high compressive residual stress was generated on the specimen surface by FPP. Rotating bending fatigue tests were performed at room temperature in laboratory air over a wide cycle-life region (103–109 cycles). In the long cycle-life regime, the fatigue strength at 107 cycles of the FPP-treated specimen became higher than that of the untreated specimen. This result is attributed to the formation of a work-hardened layer with high compressive residual stress by FPP. However, the fatigue strength was not improved by FPP in the short cycle-life regime, because fatigue cracks were initiated at surface defects formed during the FPP process. The fatigue fracture mode of the FPP-treated specimens shifted from surface-initiated fracture to subsurface-initiated fracture at a stress amplitude level of 600 MPa.

Highlights

Titanium alloys are used for implant components [1] because of their high corrosion resistance, high specific strength, lower Young’s modulus than ferrous materials, and so on
Requirements for the safety of implant components have become increasingly stringent; the fatigue behavior of titanium alloys has become a priority in fatigue research
The HAp was definitely transferred on the surface of the titanium alloy, because the amount of HAp constituent elements clearly increased

Summary

Introduction

Titanium alloys are used for implant components [1] because of their high corrosion resistance, high specific strength, lower Young’s modulus than ferrous materials, and so on. Research on the very high cycle fatigue behavior of titanium alloys is relatively scarce, compared with that on ferrous metals. Some researchers have reported that fatigue failure occurred even in the very high cycle regime for titanium alloys, such as Ti–6Al–4V [2,3,4], Ti–8Al–1Mo–1V [5], Ti–5Al–2Sn–2Zr [6], and VT3-1 [7]. Heat treatment gives β-type titanium alloys high static strength. These material properties enable β-type titanium alloys to be used to make individualized implant components with high strength

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