Effect of the initial grain size on grain refinement in Ti–2Al–2.5Zr alloy subjected to multi-impact process

Effect of the initial grain size on plastic deformation behavior and grain refinement mechanism has been investigated in Ti–2Al–2.5Zr alloy subjected to multi-impact process. The results show that grain refinement is dominated by dislocation slip in the fine-grained sample. In contrast, deformation twinning becomes prevalent in the coarse-grained one, and contributes to grain refinement by means of twin subdivision and fragmentation. Dynamic recrystallization (DRX) takes place in both samples. But, it is delayed in the coarse-grained one due to relative low fraction of grain boundaries and energy dissipation of deformation twinning. Nevertheless, the final grain size in the refined area does not show an obviously difference between the two samples at a large strain, i.e., 1.61. Moreover, grain refinement is inhomogeneous in both samples. The heterogeneity in the coarse-grained sample is much stronger than that in the fine-grained one. It was ascribed to the superimposed effect of large initial grain size and subsequent deformation twinning. A criterion for achieving an optimum grain refinement was finally suggested.