Influence of heat-treatment on the dynamic behavior of 3D laser-deposited Ti-6Al-4V alloy

In order to understand the influence of heat treatment on the mechanical property of 3D laser-deposited Ti-6Al-4V alloy, uniaxial compressive experiments were performed on the heat-treated 3D laser-deposited Ti-6Al-4V and its as-deposited counterpart under both quasi-static and dynamic loading. Meanwhile, the microstructure observation was also carried out on both as-received and deformed alloys. Based on the experimental results, the influence of heat treatment on microstructure evolution of as-deposited 3D laser-deposited Ti-6Al-4V alloy and the mechanical behaviors such as flow stress, strain hardening rate, strain rate sensitivity and fracture mechanism were investigated in detail. The results indicate that the heat treatment could improve both yield stress and compressive strength of the 3D laser-deposited Ti-6Al-4V alloy, but the plasticity of the heat-treated alloy decreased if compared with the as-deposited alloy. Moreover, remarkable strain softening was also observed in the heat-treated 3D laser-deposited Ti-6Al-4V alloy at strain rates of 1500 and 3000 s−1. Microstructure observations indicated the occurrence of adiabatic shear localization may be the main reason for strain softening. Compared with deformation twins of heat-treated Ti-6Al-4V alloy formed under the quasi-static loading, the adiabatic shear band under the dynamic loading was characterized with equiaxed nanograins induced by dynamic recrystallization.