Evidence for a phase transition in an AlCrFe2Ni2 high entropy alloy processed by high-pressure torsion.

Abstract

An as-cast AlCrFe2Ni2 high entropy alloy consisting of face-centered cubic (FCC), ordered body-centered cubic (B2) and body-centered cubic (BCC) solid solution phases was processed by high-pressure torsion (HPT) for up to 1 turn at room temperature and inspection after processing revealed a transition from the B2 and/or BCC phase to the FCC phase. An analysis by energy dispersive spectrometry showed that a reasonably homogeneous chemical composition was obtained when applying a sufficient level of torsional strain which supports the diffusional nature of the transformation. Processing by HPT gave an increase in hardness and strength but a decrease in the measured elongation in tensile testing at room temperature. The enhanced hardness and strength are due to a combination of factors including work hardening, solid solution strengthening and grain boundary strengthening. By analogy with the mechanical alloying process, it is proposed that the phase transition driven by HPT is a direct consequence of the severe shear strain which induces diffusional alloying.