The high temperature mechanical properties and the correlated microstructure/texture evolutions of a TWIP high entropy alloy

Abstract

The present work deals with the microstructure and texture evolutions of a TWIP high entropy alloy at various deformation temperatures. Toward this end, the tensile tests were conducted at temperatures ranging from 298 to 873 K under the strain rate of 0.001s(-1). The experimented material exhibited an extraordinary room temperature work hardening behavior, in respect of both the instantaneous strain hardening exponent and the work hardening rate values. This resulted in an acceptable ultimate tensile strength/ductility balance and was justified considering the high activity of twinning and planar slip. Such work hardening capacity deteriorated at higher temperatures due to increasing the dislocation annihilation rate and the stacking fault energy values that suppressed twin formation and dislocation accumulation. However, the decrease in amplitude and extent of the work hardening region was insignificant compared with other single-phase high entropy alloys. This was attributed to the high capacity of the alloy for dislocation storage at various deformation temperatures. The serrated flow was observed at 773 and 873 K due to the dynamic strain aging (DSA) mechanism. Interestingly, in this case, the DSA mechanism has a beneficial effect on overall ductility, which was attributed to the increase in the strain hardening exponent result in a delay of necking. Texture examination also reveals the formation of a double fiber texture consists of a strong <111>//TA fiber and a weaker <001>//TA fiber due to the simultaneous contribution of twinning and octahedral slip {111} <110>.