Thermal behavior and grain growth orientation during selective laser melting of Ti-6Al-4V alloy

Directional solidification causes a columnar grain microstructure with orientation deviating from building direction to the laser scanning direction which leads to anisotropic mechanical properties of deposited parts in selective laser melting (SLM) additive manufacturing (AM). However, compared to directed energy deposition (DED), the tilt angles between the grain growth orientation and the building direction in SLM are relatively small and hard to investigate due to the high scanning velocity and small facula during processing. This paper investigates the grain growth orientation in the SLM process via finite element analysis and experiments. The maximum heat flow directions and temperature gradients at different deposition heights are studied in order to discuss the local grain growth orientation. Further investigations into the differences in the grain growth orientation under different process parameters have also been carried out. In addition, the research provides a deeper understanding of the grain structures and is expected to help control the solidification texture, which is of vital importance to properties of components.