Simulation of solidified beta grain for Ti-6Al-4V during wire laser additive manufacturing by three-dimensional cellular automaton method

摘要

The beta grain of Ti-6Al-4V during wire laser additive manufacturing (WLAM) is notorious for its coarse grains and thus reducing the mechanical performance. In this research, to predict and further control the microstructure, three-dimensional (3D) beta grain evolution is simulated by 3D cellular automaton method coupled with the transient thermal profile calculated from processing modeling. Simulations are validated by experiments. The competitive growth between grains shows that the grain growth rate is less than the isotherm moving velocity, leading to a flat S-L interface, which in turn makes the orientation plays a more important role than the undercooling. It interprets the phenomena that Ti-6Al-4V grains with LeftAngleBracket;001RightAngleBracket; orientation along the building direction are preferred during WLAM. Effects of processing parameters on microstructure, such as the deposited layer, the laser power, the inter-layer time and the preheating temperature of substrate, are also investigated. Results show that the grain size at the horizon plane increases with the increase of the deposited layer, the laser power and the preheating temperature, while inter-layer time has few effects on the beta grain evolution. 3D grain simulation of additive manufacturing shows promising prospect in predicting the microstructure, revealing underlying mechanisms and optimizing processing parameters.