Heterogeneous Effects of Residual Stress and Grain Size on Tensile Behavior of Laser Shock Peened Ti-6Al-4V Alloy

Abstract

Laser shock peening (LSP) is proved to be an efficient way to improve the fatigue performance of Ti-6Al-4V alloy, which is commonly used at fan blades of aero-engines. However, there are few studies on the uniaxial tensile stress-strain responses of LSP treated materials, and no report on the constitutive modeling concerning the relationship between mechanical property and LSP effect is found. In this paper, systematical mechanical testing, microstructure characterization, constitutive modeling, and finite element simulation are conducted to investigate the tensile deformation of LSP treated Ti-6Al-4V and its connection with the underlying microstructure and deformation mechanisms. The microstructure characterization shows that grain size is refined to nanoscale in the outmost surface, and compressive residual stress is introduced in the surface region by LSP treatment. Macroscopic tensile test illustrates that the elastic modulus of LSP treated Ti-6Al-4V alloy is reduced, while the strength is elevated slightly as compared with the as-received one. A deformation-mechanism based size-dependent constitutive model, with consideration of LSP induced heterogeneously distributed residual stress and grain size, demonstrates that the gradient distributed grain size affects both the initial yielding and strain hardening of LSP treated Ti-6Al-4V alloy, while the residual stress has an important weakening effect on the initial yielding and has almost no influence on its strain hardening behavior. The established microstructure and deformation mechanisms based model can help guide the LSP processing to improve the mechanical performance of Ti-6Al-4V alloy further.