Effect of Al content on the fracture toughness and deformation behavior of Ti-Al binary alloys

Abstract

The fracture toughness and deformation behavior of Ti-xAl (x = 0, 2, 4 wt%) binary alloys were investigated. The non-thickness-dependent fracture toughness was measured based on the J-integral multiple-sample approach. Increased Al content induced reduced fracture toughness from 265 to 148 MPa·m1/2 of Ti-xAl alloys. The fracture toughness was discussed in this article by the mutual influence of the elastic component (Jel) and the plastic component (Jpl). The solid solution strengthening effect of Al was identified as the primary factor contributing to the increase in Jel. Additionally, the evolution mechanism of Jpl with varying Al content was elucidated by slip modes, twin activation, and dislocation configurations at the crack tip. Prismatic slip was found to be the predominant slip mode in Ti-xAl alloys. With the increase in Al content, the elevated critical resolved shear stress associated with prismatic slip hindered the alleviation of stress concentration, resulting in a decrease in Jpl. The increase in content of Al in the Ti-xAl alloys inhibited the formation of {11 2¯ 2} twins. Compared to Ti-0Al and Ti-2Al alloys, a significant increase in <c> dislocations was observed in Ti-4Al alloy. The additional <c> dislocations impeded the movement of subsequent <a> dislocations, which potentially resulted in a reduction in Jpl. Furthermore, a crack tip stress analysis method based on twin variant activation was proposed. In Ti-0Al and Ti-2Al alloys, twins activated by internal stress were more pronounced compared to the Ti-4Al alloy. The internal stress may be composed of back stresses, which are generated by twinning activation.