On prominent TRIP effect and non-basal slip in a TWIP high entropy alloy during high-pressure torsion processing

Abstract

Severe plastic deformation response of a face centered cubic (FCC) twinning induced plasticity (TWIP) high entropy alloy (HEA), Fe40Mn40Co10Cr10, subjected to high-pressure torsion (HPT) is investigated. The so-called TWIP HEA demonstrated an extensive transformation induced plasticity (TRIP) effect even in 1/2 turn (shear strain, gamma = 15) of HPT processing, which increased further with increasing the number of turns to 2 (gamma = 68). Additionally, HPT induced nano-structuring and heavily dislocated structure; dislocation density was of the order of 1015 m- 2. c/a ratio of the transformed HCP phase was found to be <1.633 and it did not change with increasing the extent of shear strain. This was manifested as the occurrence of at least 50% non-basal slip in the HCP phase. For the first time, the fraction of c c+a dislocations are quantified and their evolution are discussed in the purview of the studied alloy. The micro-mechanism of strain accommodation is correlated with increasing hardness of the HEA upon sequential HPT processing. The present work provides a viewpoint that the deformation induced HCP phase in a metastable FCC HEA can have tailored c/a ratio which triggers non-basal slip, leading to a strong and ductile material.