Effects of heat treatment on the microstructures and mechanical properties of as-cast Ti-45Al-2Nb-2Cr-(0.2,0.5) C alloys

Heat treatment is an effective post-processing method to modify the microstructure and mechanical properties of TiAl alloys. Thus, we report the influences of a heat treatment at 1553 K for 90 min followed by air cooling on the microstructure evolutions, strength and fracture strain of the as-cast Ti-45Al-2Nb-2Cr-(0.2, 0.5)C alloys. It reveals that the heat treatment has little effect on the phase constituents, but can cause lattice shrinkage of gamma phase due to the compressive stress of solid-state phase transition alpha ->alpha + gamma. The microstructure changes from the as-cast nearly lamellar structure to the heat-treated duplex structure, and the growth of massive gamma phase is at the expense of the (alpha 2 +gamma) lamellae. Compared with the as-cast samples, there is a significant increase in the fracture strain of the heat-treated samples, but the yield/ultimate strength shows an opposite trend. The cracks existing in the as-cast samples propagate along the lamellar interface and across the lamellae, while the cracks of the heat-treated samples are basically distributed in the massive gamma phase. Dislocations multiplication and slip within the gamma lamellae govern the plastic de -formation of the as-cast sample, while the plastic deformation of the heat-treated sample is mainly carried by the massive gamma phase. (c) 2023 Elsevier B.V. All rights reserved.

Automated summary

Heat treatment is a useful method to alter the microstructure and mechanical properties of TiAl alloys. This study investigates the effects of a heat treatment on the Ti-45Al-2Nb-2Cr-(0.2, 0.5)C alloys. The results show that the heat treatment causes lattice shrinkage of the gamma phase and changes the microstructure from nearly lamellar to duplex structure. There is an increase in fracture strain but a decrease in yield/ultimate strength for the heat-treated samples compared to the as-cast samples.