Orientation dependent plasticity of the refractory multi-principal element alloy MoNbTi investigated via micropillar compression

Refractory multi-principal element alloys (RMPEAs) are promising candidate materials for use in high temperature structural applications and other extreme environments. Recent experiments and simulations have highlighted the unusual deformation behavior of an equiatomic MoNbTi alloy, which exhibits slip on higher order planes and sluggish edge dislocation mobility. In this work, we utilize micropillar compression and postmortem transmission electron microscopy to elucidate the orientation dependent deformation behavior of MoNbTi. Our results suggest that deformation in this system is largely mediated by kink-migration of screw dislocations, as evidenced by the presence of long screw dislocations and significant dislocation debris in postmortem observations, and the absence of twinning/anti-twinning asymmetry. Moreover, we report an unusual orientation dependence of the yield strength, owing to the high stress required to facilitate slip on {110} type planes. These results further demonstrate the unconventional plasticity in BCC RMPEAs, and provide experimental verification that kink-migration is the rate limiting feature in this alloy at low temperatures.