Compositionally graded CoCrFeNiTₓ high-entropy alloys manufactured by laser powder bed fusion: a combinatorial assessment

Abstract

A modified laser powder bed fusion (LPBF) technique was utilized to fabricate CoCrFeNi high-entropy alloy (HEA) coupon with stepwise gradation (from 0 to ~12 at%) in Ti, to ascertain the maximum Ti content that can be added to the HEA for enhancing its strength. The microstructure and mechanical behavior of the fabricated coupon were investigated. High-resolution scanning transmission electron microscopy show the formations of second phases including body-centered cubic, Laves, and χ phases within the face-centered cubic matrix phase. The volume fractions of all the second phases increase with the Ti content, with a concomitant enhancement in the hardness. The observation of extensive cracking in the alloy region with ~12 at% Ti suggests that a maximum of ~10 at% Ti can be added during LPBF of CoCrFeNi HEA. A detailed analysis of the contributions of various strengthening mechanisms suggests that the second phases are the dominant contributors to the observed hardening with the Ti addition. While the Laves and χ phases induce substantial hardness enhancement, they also contribute to the cracking during LPBF of the high Ti-containing HEAs.