Simultaneous enhancements of strength and toughness by multiscale lamellar structure in Ti 2 AlNb based intermetallic

Multi-scale lamellar structure significantly improves toughness of Ti2AlNb based alloys, which are inherently brittle intermetallics, without compromising their strength. This structure was achieved throughB2-transus-forging (TBTF) combined with O + B2 two-phase region heat treatments. Various types of multi-scale lamellar structures were obtained by controlling the cooling rate after TBTF. These variations were mainly attributed to differences in the distribution, content, and size of the thick lamellar O phase and the size and crystallographic orientation of B2 grain. By analyzing the microstructural characteristics and crystallographic orientation near the crack propagation path, it was found that the crack propagation resistance of thick lamellae, sub grain and grain boundaries (GBs) O phase increased sequentially, accompanied by more tortuous crack propagation path. Moreover, B2 grains with high misorientation significantly deflected the crack propagation by cleavage ridges between adjoining cleavage planes. Additionally, the development of numerous secondary cleavage ridges, resulting from the transition through varying secondary cleavage planes in distinct sub B2 grains, further hindered the quick propagation of cracks. It was clarified that the cleavage planes were dominantly belonging to {110}. These findings provided valuable guidance for the design of damage tolerance strategies for Ti2AlNb-based intermetallics. (c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

Multi-scale lamellar structure significantly improves the toughness of Ti2AlNb based alloys without compromising their strength. The formation of this structure depends on the cooling rate and the distribution and size of O phase and B2 grains. The presence of thick lamellar, sub grain, and grain boundary O phases effectively obstructs crack propagation and makes the crack path tortuous.