Investigation on transformation-related recrystallization behavior of Ti2AlNb-based alloy

Abstract

To achieve grain refinement, the recrystallization behavior of B2 matrix phase in a Ti2AlNb-based alloy was investigated by performing a series of thermal compression tests at temperatures in the range of 950~1025°C with strain rates from 0.001s−1 to1s−1. Instead of water quenching immediately after deformation, samples were further held at deformation temperature for a certain time, in order to make the heat-affecting time at various strain rates consistent. Electron back scattered diffraction (EBSD) technique was employed for microstructure analysis, in combination with grain orientation spread (GOS) method to distinguish recrystallized grains from non-recrystallized grains. The results reveal that: (i) dynamic recrystallization (DRX) is not easy to occur in this alloy, and increasing strain rate leads to a decrease of DRX fraction; (ii) when evaluated on the same time scale, the sample at strain rate of ε˙=0.1s−1 has the highest recrystallized fraction among all applied strain rates, which provides sufficient nucleation rate of DRX as well as notable grain growth during post-dynamic recrystallization (PDRX); and (iii) the recrystallization evolution with temperature changes is closely linked to the phase transformation in Ti2AlNb. The presence of O and α2 phases affects recrystallization process via pinning effect and particle stimulated nucleation (PSN) mechanism. This work therefore provides a new understanding of recrystallization behavior during and post deformation of Ti2AlNb-based alloy, which is meaningful to refine grains by combining the contributions of DRX and PDRX.