Ex-situ study on mechanical properties and deformation mechanism of three typical microstructures in TA19 titanium alloy

The near-alpha titanium alloy TA19 with three typical microstructures (lamellar, equaixed and bimodal microstructure) were compressed, accompanied by ex-situ observation on the slip trace and crack nucleation, which aimed to reveal the dependence of mechanical properties on microstructure based on analyzing the deformation mechanism. The results revealed that the lamellar microstructure had the lowest yield strength because of very large colony size. Meanwhile, although the equiaxed a grain size in equiaxed microstructure was similar to the size of equiaxed alpha grain and alpha colony in the bimodal microstructure, the strengthening effect of alpha/beta interface in alpha colony made the bimodal microstructure possess the highest yield strength. The fracture strain was strongly influenced by the crack nucleation and propagation in different microstructures. It was found that the largest alpha colony size induced an earliest crack nucleation and easy crack propagation in the lamellar microstructure, and then resulted in the smallest fracture strain. Conversely, the small size of alpha grain and colony induced a higher fracture strain in the equiaxed and bimodal microstructure. Furthermore, the intergranular beta phase could coordinate the deformation between the two adjacent alpha grains and benefit the fracture strain in the equiaxed microstructure.