Twinning-induced plasticity (TWIP) effect in multi-phase metastable beta Zr-Nb alloys

Abstract

• Twinning-induced plasticity (TWIP) strategy was first applied in Zr alloys for strain-hardening and ductility enhancements. • Zr-13.8Nb-0.7Hf and Zr-15.5Nb-0.7Hf alloys designed by electron-to-atom ratio exhibit multi-phase microstructures consisting of acicular body-centered tetragonal phase and monoclinic phase in beta grains. • TWIP-enhanced Zr-13.8Nb-0.7Hf alloy resulted in superior strain-hardening rate and ductility when comparing to Zr-15.5Nb-0.7Hf without mechanical twinning. • In-situ traction tests in TEM and SEM-EBSD were conducted to clarify the {332}<113> twinning operation and its interaction with body-centered tetragonal phase. The deformation mechanisms were studied in metastable Zr-13.8Nb-0.7Hf and Zr-15.5Nb-0.7Hf (wt.%) alloys exhibiting complex microstructures due to quenched-in precipitates (acicular body-centered tetragonal phase and globular monoclinic phase) in beta grains. Twinning-induced plasticity (TWIP) effect was observed in Zr-13.8Nb-0.7Hf via {332}<113> twinning operation, resulting in higher strain-hardening rate and uniform elongation than those of Zr-15.5Nb-0.7Hf deforming via only dislocation glide. In-situ characterizations, by applying tensile deformation during electron backscattered diffraction (EBSD) mapping and transmission electron microscopy (TEM) observation, were conducted to clarify the twinning process and the role of quenched-in precipitates when interacting with deformation twins.