Hot deformation behaviors of an ultrafine-grained MoNbTaTiV refractory high-entropy alloy fabricated by powder metallurgy

The hot deformation behaviors of an ultrafine-grained MoNbTaTiV refractory high entropy alloy (RHEA) fabricated by powder metallurgy (P/M) were investigated using isothermal compression tests in the deformation temperature range of 1100 degrees C similar to 1300 degrees C and the strain rate range of 0.0005 s(-1)-0.5 s(-1). Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques were used to analyze the effect of the deformation temperatures and the strain rates on the flow stress behaviors and microstructural evolution during hot deformation. The results showed that the flow stresses exhibit typical dynamic recrystallization (DRX) characteristics, but show work hardening characteristics at 1100 degrees C and 0.5 s(-1) deformation conditions and at 1200 degrees C and 0.5 s(-1) deformation conditions. With increasing deformation temperature and decreasing strain rate, the maximum compressive stresses were dramatically decreased, and the average grain sizes also slowly increased. The limited growth of grains was due to the sluggish diffusion effect of high entropy alloys (HEAs) and the pinning effect of the ultrafine precipitated phases. The dominant DRX process gradually changed from discontinuous dynamic recrystallization (DDRX) to continuous dynamic recrystallization (CDRX) with increasing deformation temperature and decreasing strain rate. Both of these DRX processes were promoted by the ultrafine precipitated phases. The dominant deformation mechanism at low deformation temperature and high strain rate was grain deformation. Grain boundary gliding became the dominant deformation mechanism at higher deformation temperature and lower strain rate, but it was inhibited to some extent by grain growth and the ultrafine precipitated phases distributed at grain boundaries.