Improvement of low-cycle fatigue properties in electron beam powder bed fusion processed Ti-6Al-4V alloy by laser shock peening

In this study, laser shock peening (LSP) was applied to modify the surface microstructure and low-cycle fatigue (LCF) performance of electron beam powder bed fusion processed Ti-6Al-4V titanium alloy. The microstructure evolution, fatigue crack propagation, deformation behavior, and residual stress without and with LSP were compared to explore the role of gradient microstructure on the LCF behavior. The gradient microstructure induced by LSP is composed of nanograins and submicro-equiaxed grains. Moreover, the degree of work hardening near the surface of LSP-treated samples becomes higher after fatigue loading, which alleviates the cyclic softening behavior. The residual compressive stress within the surface layer experiences a 20 % reduction under high strain amplitude, yet there is still a uniformly distributed compressive residual stress layer at the deeper subsurface. A deeper gradient microstructure, work hardening layer, and compressive residual stress triggered via LSP can restrain the crack initiation and propagation, reduce the cyclic softening rate, and thus improve the LCF performance.