Prediction of solidification microstructure of titanium aluminum intermetallic alloy by laser surface remelting

• A numerical model for predicting solidification microstructures was developed. • The variation trend of dendrite arm spacing with process parameters was revealed. • Dendrite arm spacing of TiAl alloys mainly depends on the temperature gradient. By controlling the processing parameters in the laser additive manufacturing (LAM) process, the mechanical properties of titanium aluminum alloy could be modified. However, the difficulty of optimizing the solidification microstructure is to build the relationship between the microstructure and processing parameters. To solve this problem, a numerical model of combined processing parameters with dendrite arm spacing was developed in this paper to predict the solidification microstructure and reveal the effects of laser processing parameters on dendrite arm spacing. A geometry factor (α) was first introduced in the prediction model to correct the simulated molten pool shape to improve prediction accuracy. Moreover, the nonequilibrium solidification of LAM due to fast cooling was taken into consideration in this study. Based on the model, primary dendrite arm spacing (PDAS) and secondary dendrite arm spacing (SDAS) in laser surface remelting of Ti-47Al-2Cr-2V alloy were investigated in combination with simulations and experimental observations. The experimental results indicate that the model calculated using average solidification conditions applies well in predicting the solidification microstructure of titanium aluminum alloy. The dendrite arm spacing slightly decreases at low scanning velocity but increases at high scanning velocity as the laser power increases. In addition, the scanning velocity plays a dominant role in the change in dendrite arm spacing when the scanning velocity is lower than 600 mm/min, and the impact of laser power on dendrite arm spacing gradually increases as the scanning velocity increases.