Effects of cycle heat treatment on the microstructure and mechanical property of as-cast ?-TiAl alloy

Cyclic heat treatment has been applied to improve the microstructure and properties of the as-cast Ti-46Al-1Cr-2V alloy. The grain size was refined from millimeter scale to about 40 mu m, and the elongation at room temperature increased from 0.62% to 1.52%. The treated alloy shows excellent tensile strength and plasticity at 800 degrees C due to the fine grain strengthening and complex twinning movement. The cyclic heating and cooling near eutectoid temperature promoted the formation of a large number of dislocations in the gamma phase, and promoted the nucleation of secondary alpha 2 (alpha s) phases and gamma twins. During the heating process, four secondary alpha s phases with different orientation were formed on the corresponding close-packed planes of the gamma phase. The movement of the Shockley partial dislocations required for the growth of alpha s phase was affected by the lomer-cottrell dislocations when it meets the dislocation of adjacent close-packed planes, which hindered the growth of alpha s phase. The nanometer-thick Ti2Al phase with high distortion energy would be formed on the ledge surface between alpha s phase and gamma phase to ensure the transition of the two phases in crystal structure and chemical composition, and the Ti2Al phase also had a direct inhibitory effect on the growth of alpha s phase.