The investigation of high-temperature shear deformation mechanism in Ti-44Al-4Nb-1.5Mo-0.1B alloy

Abstract

TiAl alloys are attractive as promising aerospace structural materials. The high-temperature deformation performance of the intermetallic can be enhanced through controlled thermal mechanical processing and microstructure. This study utilized shear compression specimen (SCS) to investigate the shear deformation on the deformability and microstructure of Ti-44Al-4Nb-1.5Mo-0.1B (TNM) alloy. The compression test demonstrates that, compared to traditional symmetric deformation, shear deformation exhibits several advantageous characteristics: a low deformation stress (109.8 MPa), a slow dynamic softening, a large deformation conditions, and a low activation energy (163.3 kJ/mol). The good thermal deformation properties are related to the microstructure. During the shear deformation process, microscale shear bands (MSBs) are gradually formed under the combined effect of elemental enrichment and lattice distortion as the force at the α₂/γ interface in the lamellae increases. The internal stress values of MSBs are 5–10 times greater than at a typical α₂/γ interface, which promotes the nucleation of dynamic recrystallization (DRX). The evolution of the structure can be classified into two types such as high temperature and low strain rate, as well as low temperature and high strain rate. Under high temperatures and low strain rates conditions, deformation was primarily occurring in DRX. Shear deformation not only activates dislocation slip but also significantly promotes the formation of nanotwins, which in turn facilitates the nucleation of DRX. Under low temperatures and high strain rates conditions, the MSBs, DRX, and broken lamellae work together to coordinate the deformation. In conclusion, shear deformation can improve the thermal processing performance of TNM alloys, which is an effective means of molding TNM alloys.