A simulation and experiment study on phase transformations of Ti-6Al-4V in wire laser additive manufacturing

The additively manufactured Ti-6Al-4V part suffers from undesirable α^′ phase, which leads to a decrease of its plasticity. In this research, density-based constituent phase simulation method is applied to investigate the phase transformation of Ti-6Al-4V during wire laser additive manufacturing (WLAM). Single-layer and five-layer WLAM experiments are conducted to validate the accuracy of the simulation. The simulation results agree with the experimental results. By in-situ investigating the phase transformation during cooling, it is found that there exist four stages for β→α/α^′, which are (I) β→α_gb/α_C, (II) β→α_B, (III) β→α′ and (IV) β→α_B and α^′→α_B+β. Increasing the temperature and decreasing the cooling rate help in narrowing or even eliminating the β→α′ stage, which finally leads to the decrease of α^′ fraction or even avoid its formation. Compared with the laser power 2500 W case, the laser power 3000 W case gets more transformed α_B without increasing α-lath thickness. The simulation shows promising prospects in predicting phase transformation, revealing underlying mechanisms and optimizing processing parameters.