The effect of V element segregation on the mechanical properties of TC4 titanium alloy welded joint in heat treatment process

In this paper, during the heat treatment of TC4 titanium alloy pulsed laser-arc hybrid welded joints, it was found that the degree of V elemental segregation in the beta phase of the weld microstructure increased with the slowing down of the cooling rate after holding the weld joint for a certain period above the beta phase transition temperature. To reveal the effect of V element segregation in the beta phase on the mechanical properties, tensile simulations were carried out using molecular dynamics at different temperatures for different degrees of segregation in the model. The results showed that at the same temperature, when the V elements were segregated in the beta phase, the energies of the models were all lower than that of the model with uniform distribution of V elements after relaxation. At the same time, the tensile strengths were all higher than that of the model with a uniform distribution, and the tensile strengths in the x- and y-directions were increased by 17.7% and 8.1%, respectively. In stretching to the maximum stress, the deformation mainly occurred in the beta phase, and the deformation mode was a phase transition from BCC to HCP with the formation of nanocrystalline. However, with the increase in temperature and the decrease of the degree of V elemental segregation, the nanocrystalline formed by the deformation gradually decreased, and the grain boundaries also became irregular, which was the main reason for the decrease in the tensile strength. At the same time, after segregation, the start of the BCC phase transition in the tensile process was delayed, which was also beneficial to improving the strength of the model. After exceeding the tensile strength, the deformation was mainly dominated by the slip of dislocations. In addition, with the increase of the degree of V element segregation, the difference in the tensile strength of the model tensile along the parallel and perpendicular grain boundary directions decreased from 0.48 to 0.18 GPa, and the anisotropy of the material was weakened.