Characterization of deformation in primary alpha phase and crack initiation and propagation of TC21 alloy using in-situ SEM experiments

In present work, the localized deformation, crack initiation and propagation behavior of Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-0.1Si (TC21) titanium alloy was investigated through the in-situ scanning electron microscope (SEM) test and electron backscatter diffraction (EBSD). The results indicate that deformation in alpha phase is mostly accommodated by the prismatic slip. The localized deformation is concentrated at the interface of primary alpha lath. Some parallel slip bands with prismatic and pyramidal slip are prevalent in primary alpha lath, while the multiple slip bands with prismatic slip are dominant in equiaxed primary alpha phase. Higher ability to coordinate local plastic strain (nearly to 79.5%) is induced in equiaxed alpha than the primary alpha lath (7.9%). Most of the cracks easily initiate at the shear bands in primary a lath, which is a fatal site for the tensile deformation. The main crack propagates quickly along the shear bands or interfaces of alpha lath and then penetrates into the beta(trans) matrix and also transfers across the equiaxed alpha phase along the slip bands. The results indicate that the high compatibility of deformation in equiaxed primary alpha phase delays the initial crack nucleation. Whereas, it does not show satisfied resistance against crack propagation in front of the main crack tip due to the abundant slip bands.