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

Abstract

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 μm, and the elongation at room temperature increased from 0.62% to 1.52%. The treated alloy shows excellent tensile strength and plasticity at 800°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 γ phase, and promoted the nucleation of secondary α2 (αs) phases and γ twins. During the heating process, four secondary αs phases with different orientation were formed on the corresponding close-packed planes of the γ phase. The movement of the Shockley partial dislocations required for the growth of αs phase was affected by the lomer-cottrell dislocations when it meets the dislocation of adjacent close-packed planes, which hindered the growth of αs phase. The nanometer-thick Ti2Al phase with high distortion energy would be formed on the ledge surface between αs phase and γ 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 αs phase.