Microstructure and mechanical properties of the new TiZrHfReAl HCP high entropy alloy

ABSTRACT In the present study, the intelligent addition of Re and Al to TiZrHf equiatomic ternary alloy resulted in a new single-phase Ti30Zr30Hf30Re5Al5 HCP high entropy alloy. The XRD analyses show that the TiZrHfRex alloys have a single-phase HCP structure until x = 5 at.%. Subsequently, the TiZrHfRe5 retains its single-phase HCP microstructure with the addition of Al upto 5 at.%, leading to a new quinary TiZrHfRe5Al5 HCP HEA. Microstructural investigations using SEM revealed the formation of compositionally homogeneous single-phase HCP solid solution for TiZrHf, TiZrHfRe5 and TiZrHfRe5Al5 alloys. Vicker's microindentation measurements revealed that adding Re, followed by Al, increases the hardness of the TiZrHf ternary alloy from 7.85 0.37–8.35 0.42 GPa. In a nutshell, a novel quinary HCP alloy was developed based on transition metals, allowing HCP HEA compositional space to expand beyond rare-earth (RE) based HEAs.