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

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 degrees 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 degrees 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 degrees 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 degrees C, the peak stress of the second stage of the sample decreased successively. At 700 degrees 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 degrees 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.

Automated summary

The study showed that at 600°C, the peak stress of Zr was higher in the second stage than the single-stage test, without static softening; at 800°C, the peak stress was lower than the single-stage test, with rapid static softening occurring; at 700°C, the peak stress of the second stage decreased gradually with increasing holding time.