High temperature deformation behaviors of polysynthetically twinned (PST) Ti–47Al–2Cr–2Nb alloy

The characteristics of deformation and fracture of polysynthetically twinned (PST) Ti–47Al–2Cr–2Nb alloy at 800°C had been identified by scanning and transmission electron microscopy. The tensile properties of the fully laminated Ti–47Al–2Cr–2Nb showed anisotropy for three different orientations (N, P and I orientation) at elevated temperature. Some differences in fracture modes between three oriented-lamellae at 800°C had been observed, which were mainly due to the normal stress and shear stress. Also, it was found that the α2-lamellae decomposed and the γ-lamellae coarsened during high temperature deformation, but similar tendency was more obvious in hard orientation. At last, the deformation modes had been identified by transmission electron microscopy. For the hard orientation loaded PST Ti–47Al–2Cr–2Nb samples (N and P orientation) all variants of γ-lamellae deformed only by hard dislocation slip and hard twinning. While the γ-lamellae deformed more profusely for soft orientation loaded PST Ti–47Al–2Cr–2Nb sample (I orientation). It was observed that a majority of γ-variant lamellae deformed by the soft modes of parallel twinning and by soft ordinary dislocation glide and hard modes of twinning as well as hard dislocation activity had been observed for the remainder of the variants of γ-lamellae in the soft orientation loaded PST-TiAl.