Numerical Simulation of Temperature Field Distribution During Directional Annealing of TiAl Alloy with Different Parameters

In this paper, a bidirectional temperature gradient directional annealing process for growing TiAl columnar crystals was proposed, and the influences of structural parameters and process parameters on the temperature distributions of TiAl rods were discussed through numerical simulation. The results indicate that the α phase zone is expanded and its boundary becomes planar as the thickness of graphite ring (b) and gap width (d) decrease. Increasing the graphite rod length (l) and the height of the graphite ring from the Ga-In coolant surface (h) results in an expanded α phase zone with flattened boundaries, but the temperature gradient decreases. Taking all the α phase zone height, its boundary shape, and the temperature gradient into consideration, the optimal b, d, l, and h are 10 mm, 5 mm, 50 mm, and 50 mm, respectively. The higher heating temperature within the α phase temperature range, such as 1375 °C, is favorable for the establishment of the required temperature field during directional annealing. The effect of drawing speed is more complicated. Although its effect on the temperature field of the TiAl rod is almost negligible, it will seriously affect the microstructure of the annealed alloy, and it needs to be optimized by subsequent experiments.