Laser shock peened Ti-6Al-4 V alloy: Experiments and modeling

Abstract

Systematical microstructure characterization, mechanical testing and constitutive modeling were carried out to quantify the effects of residual stress and grain refinement on tensile properties of Ti-6Al-4 V alloy treated by laser shock peening (LSP). Microstructure characterization showed that grain size is refined to nanoscale in the outmost surface. Meanwhile, LSP treatment introduced a maximum compressive residual stress of 600 MPa in the surface region. The macroscopic tensile test indicated a more prolonged elastic-plastic transition in the LSP-treated Ti-6Al-4 V alloy than the as-received one. As a result, the 0.2% offset yield strength of the LSP-treated Ti-6Al-4 V alloy was reduced by about 52 MPa, while the flow strength at the subsequent strain hardening stage was enhanced. To quantitatively evaluate the individual influence of gradient microstructure and residual stress on the tensile response, we established a deformation-mechanism-based and size-dependent constitutive model. Implementation of the constitutive model demonstrated that the surface grain refinement enhances both the initial yielding and strain hardening of LSP-treated Ti-6Al-4 V alloy. In contrast, the residual stress has a significant weakening effect on the initial yielding but has little influence on its strain hardening behavior. The established microstructure and deformation mechanism-based model can help guide the LSP processing to further improve the mechanical performance of Ti-6Al-4 V alloy.