Modeling and simulation of the columnar-to-equiaxed transition during laser melting deposition of Invar alloy

The morphology of microstructure affects the quality of Invar alloy mould when it is repaired with laser melting deposition (LMD). However, it is quite hard to observe the evolution of microstructure in real time. The current study adopted a CA-FE model, i.e, cellular automaton coupled with finite element, to simulate the microstructure evolution of Invar alloy in the LMD process. The mechanism of columnar-to-equiaxed transition in the molten pool was investigated based on the simulation results. In addition, an analysis was completed by comparing the simulation with the experimental results, which verified the feasibility of simulating the microstructure evolution with the CA-FE model in the LMD process. The results indicated that the bottom of the molten pool is filled by the epitaxial growth of columnar grains and the orientation of the columnar grains is consistent with the direction of the maximum temperature gradient in the molten pool. The top of the molten pool is occupied by equiaxed grains. This study provides a referenced value on the quality improvement of the mould repaired by LMD.