Using Cavitation Peening to Improve the Fatigue Life of Titanium Alloy Ti-6Al-4V Manufactured by Electron Beam Melting

Osamu Takakuwa,Mitsuo Niinomi,Mitsuru Sato,Masaaki Nakai,Fumio Takeo,Hitoshi Soyama

doi:10.4236/msa.2016.74018

Abstract

Although Electron Beam Melting (EBM) is an innovative technology, the fatigue properties of materials manufactured by EBM may be lower than those of casted and wrought materials due to defects and surface roughness. In order to enhance the fatigue life of components or structures manufactured by EBM, a mechanical surface treatment technology, e.g., peening, would be effective because peening introduces high compressive residual stress at the surface which can extend the fatigue life considerably. In the present study, specimens were manufactured by EBM using titanium alloy Ti-6Al-4V powder. Two types of specimens were prepared: as-built and as-machined specimens. Specimens of each type were treated by cavitation peening or shot peening. The fatigue lives of the specimens were evaluated by a plate bending fatigue tester. The residual stress and surface roughness were also evaluated. The results obtained showed that the fatigue strength of as-built specimens can be improved by 21% by cavitation peening or shot peening, and the fatigue life under particular applied stresses can also be extended by 178% by cavitation peening.

Highlights

Electron Beam Melting (EBM) has been developed as an innovative technology for the rapid manu-How to cite this paper: Sato, M., Takakuwa, O., Nakai, M., Niinomi, M., Takeo, F. and Soyama, H. (2016) Using Cavitation Peening to Improve the Fatigue Life of Titanium Alloy Ti-6Al-4V Manufactured by Electron Beam Melting
For the as-machined specimens, we focused on fatigue lives of less than 106 cycles
In order to examine the combined effect of the compressive residual stress and surface roughness on fatigue failure, we introduce a parameter, Rσ*, given by Equation (4) [26], in which the compressive residual stress has a positive effect and the surface roughness has a negative effect on the fatigue life: Not peened

Summary

Introduction

Electron Beam Melting (EBM) has been developed as an innovative technology for the rapid manu-. To enhance the fatigue properties, some mechanical surface treatment technologies have been developed, e.g., shot peening and cavitation peening. It has been demonstrated that the compressive residual stress introduced by peening prevents fatigue crack propagation in metallic materials [7]. An innovative mechanical surface treatment, cavitation peening, utilizes the impact produced by shock waves in water caused by cavitation bubbles collapsing [10]. It can be utilized in the same way as shot peening. The components manufactured by EBM need to be improved in terms of their fatigue properties, and cavitation peening has the potential to do this. The compressive residual stress at the surface introduced by peening was evaluated by X-ray diffraction stress measurements

Experimental Facilities and Procedures

Results and Discussion

Conclusions