Dynamic and static softening mechanisms of commercial-purity Zr during double-stage hot compressive deformation

Abstract

The dynamic and static softening behavior of R60702 commercial-purity Zr was studied through single-stage and double-stage uniaxial hot deformation tests in the range of 600oC–800 °C. The microstructural evolution to uniaxial compression loading for the different conditions was investigated using a combination of optical microscopy and electron back-scattering diffraction (EBSD). The results show that the static softening fraction increases with an increase in temperature as well as holding time. At 600 °C, the peak stress of the second stage was greater than that of the single-stage, and the sample did not undergo static softening. At 800 °C, the peak stress of the second stage was less than that of the single-stage, and the sample underwent rapid static softening during holding time. As the holding time increased at 700 °C, the peak stress of the second stage of the sample decreased successively. At 700 °C and 1s holding time, the sample did not undergo static softening, and dynamic recovery and recrystallization occurred in the subsequent second stage. At 700 °C and 60s holding time, the sample underwent static recovery and recrystallization; larger grain growth and deformation appeared in the subsequent second stage. This change in the microstructural morphology with the flow stress curve is discussed in the subsequent sections.