Prediction of microstructure in selective laser melted Ti 6Al 4V alloy by cellular automaton

Selective laser melting (SLM), as a powder-bed-based additive manufacturing technology, is a promising technology for manufacturing metal parts with high geometric complexity. The prediction of the SLMed microstructure, a key approach to manipulate the microstructures and performances, is challenging due to the complex heat history involving multiple thermal cycles. In the work, the microstructural simulation of solidification and solid-state phase transformation processes under various spatially variable thermal cycles of SLM was investigated by a developed two-dimensional cellular automaton (CA) model considering the temperature distribution and transient thermal history. The morphology and size of the β grain and martensite simulated by the model agree well with the experimental results in single-layer, thin-wall and multi-track multi-layer samples. Based on the simulated results, there are three zones (powder melting, remelting and reheating zones) and four stages (powder melting, mushy, multi-phases and solid-state phase transformation stages) during SLM depositing Ti-6Al-4V alloy. The morphology, growth direction and size of prior β grains depend mainly on the direction of heat flux and overlapping of adjacent deposited tracks. Six evolutional types of β grains exist including disappearance, morphological change, size increasing to be a stable value, growing, size decreases to be a stable value, and no evolution. The prediction of microstructure in SLMed alloy can be realized by the developed CA model.