Controlling grain boundary character distribution of high-temperature B2 phase in Ti–Ni–Fe alloy

Abstract

A method is proposed for controlling the grain boundary character distribution of high-temperature B2 phase in Ti–Ni–Fe alloys. The method utilizes the lattice correspondence between the deformation twins in B19′ martensite and the residual planar defects in the B2 parent phase. The optimal conditions for recrystallization and additional annealing of the tensile-deformed specimen with residual strain of about 20% were determined to be 873 K for 0.9 ks and 773 K for 3.6 ks, respectively. In the specimen annealed under these optimal conditions, over 90% of grain boundaries were coincidence boundaries with Σ ≤ 27. In particular, 33% of the grain boundaries were low-angle boundaries, that is, Σ1 boundaries. The atomic structures of the Σ9 coincidence grain boundaries and the Σ1 low-angle boundaries were observed by high-angle annular dark field scanning transmission electron microscopy. The atomic structure of these boundaries was explained well by theoretical predictions.