Effect of ultrasonic surface deep rolling combined with oxygen boost diffusion treatment on fatigue properties of pure titanium

Xue-Fei Teng,Cheng-Cheng Zhang,Yun-Fei Jia,Shan-Tung Tu,Cong-Yang Gong,Xian-Cheng Zhang

doi:10.1038/s41598-021-97255-x

Abstract

Ultrasonic surface deep rolling (USDR), oxygen boost diffusion (OBD), and their combination (USDR-OBD) were all used to improve the surface hardening of pure titanium. The microstructure, microhardness, and fatigue life of pure titanium treated by USDR, OBD, and USDR-OBD methods were analyzed. USDR treatment induced a severe deformation area, while OBD treatment produced a brittle oxygen diffusion zone. The USDR-OBD treated samples approached the highest hardness in comparison with other treated samples. The fatigue lives of USDR treated samples were improved, which was due to the high compressive residual stress and refined grains. However, the fatigue lives of both OBD treated samples and USDR-OBD treated samples were decreased due to premature crack initiation and rapid propagation in the oxygen diffusion zone. Finally, the fatigue fracture mechanisms of different samples were proposed.

Highlights

Ultrasonic surface deep rolling (USDR), oxygen boost diffusion (OBD), and their combination (USDR-OBD) were all used to improve the surface hardening of pure titanium
The average hardness of the AN series and R series are both 180 HV, which is shown as a benchmark line. It can be seen, compared with USDR series, the USDR-OBD series achieved a significant enhancement of hardness near the surface
(2) USDR treatment improved the fatigue life of pure titanium, which was attributed to the high compressive residual stress and refined grains in the near-surface region

Summary

Introduction

Ultrasonic surface deep rolling (USDR), oxygen boost diffusion (OBD), and their combination (USDR-OBD) were all used to improve the surface hardening of pure titanium. Compared with thermal oxidation treatment, the OBD treatment can effectively improve surface hardness and wear resistance due to the generation of the thick oxygen diffusion zone (ODZ)[9]. Being restricted by the reaction kinetics, the pursuit of a thicker ODZ generated by the method of increasing temperature or prolonging reaction time was not practical[10] To overcome this issue, an increasing number of studies have focused on surface duplex treatment, especially on the grain refinement process followed by thermochemical treatment. The result shows the fatigue limit had not been effectively improved, regardless of the order of severe shot peening and nitriding. The fatigue lives of pure titanium treated by USDR, OBD, and USDR-OBD combination method were explored

Methods

Results

Conclusion