Dynamic strain aging and twin formation during warm deformation of a novel medium-entropy lightweight steel

The present study deals with the extraordinary twin formation during compressive deformation of a Fe-37.55Mn-8.5Al-0.6C (wt.%) low-density steel at warm temperature regime (200–600 °C). Despite the conventional opinion regarding the restrictive effect of increasing temperature on the occurrence of deformation twinning, not only the twin boundary fraction did not decrease, but also twinning was encouraged at 400 °C and even 600 °C. This was discussed relying on the occurrence of dynamic strain aging phenomenon, which caused a bump in corresponding hardening rate curves. The medium entropy of the alloy, which made short-range diffusion of solute atoms feasible and facilitated local pinning of the mobile dislocations, provided a proper condition for the occurrence of high temperature strain ageing. Finally, the unbalanced pinning of trailing and leading dislocations influenced on their velocity and caused widening the stacking faults which in-turn could significantly assist deformation twinning at such high deformation temperatures.