Initial orientation analysis of the contribution of pyramidal 〈c+a〉 slip to the dynamic recrystallization in a Zr-1Sn-0.3Nb alloy under warm to hot deformation

In this work, a Zr-1Sn-0.3Nb alloy plate was compressed to a true strain of 0.85 at a constant strain rate of 0.001 s⁻¹ over wide temperature ranges (300 °C, 550 °C, 600 °C, 650 °C and 700 °C) with the aims of investigating the dynamic recrystallization (DRX) mechanisms and the effect of pyramidal 〈c+a〉 slip on the DRX mechanisms. In particular, compression deformations were carried out along the normal direction (0° sample), where basal and pyramidal 〈c+a〉 slip occurred mainly, and along the transverse direction (90° sample), a condition in which predominant prismatic and basal slip contributed to the deformation. The deformed microstructures were investigated in detail by electron backscatter diffraction (EBSD), transmission kikuchi diffraction (TKD) and transmission electron microscope (TEM). Microstructure evolution indicated that the mechanisms of new grain formation changed from continuous to discontinuous reaction with increasing deformation temperature. When deformed at 300 °C, compression along the axes of the grains enhanced continuous DRX (CDRX), leading to the generation of ultra-fine grains. When deformed at 550–700 °C, with increasing temperature, the critical stress and critical strain determined from the true stress-true strain curves decreased, while the volume fractions of recrystallized grains and high angle boundaries (HABs) increased, suggesting that DRX kinetics was promoted at higher temperatures due to the sufficient thermal energy. On the other hand, the DRX mechanism for deformation along normal direction was discontinuous DRX (DDRX) followed by CDRX and along transverse direction was CDRX. However, the recrystallized grain size was insensitive to the deformation direction. The simultaneous operation of prismatic , basal and pyramidal 〈c+a〉 slip provided enough stored energy for the onset of DDRX. Moreover, the stored energy of deformation driving generating recrystallized grains was confirmed by the similar fraction of recrystallized grains and grain boundary misorientation distribution in both 0° and 90° samples deformed at 700 °C.