Effect of severe shot peening and ultra-low temperature plasma nitriding on Ti-6Al-4V alloy

Abstract

In this study, the fatigue behavior of Ti-6Al-4V alloy is tend to be improved by severe plastic deformation via shot peening and plasma nitriding. Shot peening with sub-branches: Conventional shot peening (A12-14), severe shot peening (A28–30 and A34-36) and repeening (N6-8) are exposed. Besides plasma nitriding is implemented at 500 °C, 550 °C and 600 °C with the durations of 4, 8 and 16 h. Due to utilization of shot peening as prior severe plastic deformation during diffusion of nitrogen, two methods are applied in sequence. Severe shot peening forms ultra-fine crystals and oriented grains by disintegrating of α and β phases just below the surface and increases surface roughness. Plasma nitriding temperature increase the compound layer thickness and the treatment leads to vanish of β particles through a certain line for diffusion layer. Prior severe plastic deformation by severe shot peening generally triggers the formation of thicker compound layer and emerges distinct diffusion depth with finer and oriented precipitation. The phase's intensity obtained from XRD peaks has been amplified by the application of prior shot peening. Each shot peening provides fatigue improvement on the other hand plasma nitriding application regardless of being pre or post treatments diminish the fatigue resistance.