Dynamic Behavior of Additively Manufactured FeCoCrNi High Entropy Alloy

Abstract

Additively manufactured face-centered-cubic high entropy alloys have a combination of high strength and good ductility, and are promising impact-resistant structural materials. However, the dynamic behavior of additively manufactured face-centered-cubic high entropy alloys is seldomly reported. In this study, FeCoCrNi high entropy alloy was fabricated, using the laser beam powder bed fusion technique, and dynamic tests were performed by means of a Split Hopkinson Pressure Bar. The high entropy alloy showed a more excellent combination of yield stress and toughness at high strain rates, than previously reported alloys. This was attributed to the dislocation cell structure of the additively manufactured FeCoCrNi HEA, which provided high local stress concentration, leading to the formation of microbands and deformation twins. The high entropy alloy showed higher strain rate sensitivity than the cast counterpart, at both quasi-static and strain rates over 3000 s−1. Interestingly, the yield stress kept stable at a strain rate from 1000 s−1 to 3000 s−1, showed a steep decrease of strain rate sensitivity and a four-fold increase in activation volume, implying a transition in deformation mechanism to collective dislocation nucleation.