Numerical and experimental study of directional annealing to prepare columnar grains of TiAl alloy

Directional annealing (DA) is a novel technique to prepare colunmar grains or single crystal in TiAl alloys without melt contamination. Both numerical simulation and experiments were conducted to investigate the directional annealing (DA) of a Ti48Al alloy in this paper. The temperature distribution of the TiAl rod under different DA parameters were calculated and discussed by Finite Element (FE) method. The results showed that the temperature field was significantly influenced by hot zone temperature, moving rate of induction coil, rod diameter and cooling condition. Once induction heating started, the temperature of Ti48Al rod rose rapidly and reached a steady state after about 400 s. The effective heat area (single phase zone) enlarged with the increase of preset temperature. With the decreasing movement rate of induction coil, the α/α+γ interface became more planar, and this rule also applied to the effect of the rod diameter on α/α+γ interface. Under the guidance of calculation results, optimized parameters were proposed to directionally annealing Ti48Al alloy. Rods with a diameter of 8 mm were induction-heated under the hot zone temperatures of 1673 K and 1693 K correspondingly. In the range of α single phase, the transformation of γ→α phase occurred completely and α grains directionally coarsened with the movement of hot zone. In this way, columnar grains in Ti48Al alloy were successfully formed in a solid state.