Significant enhancement in tensile strength and work hardening rate in CoCrFeMnNi by adding TiAl particles via selective laser melting

In this study, 4 at.% Ti-48Al-2Cr-2Nb (TiAl) powder particles were added into CoCrFeMnNi high entropy alloy (HEA) and processed by selective laser melting (SLM) followed by hot isostatic pressing and ageing with the aim of enhancing its strengths. It was found that the as-developed HEA-TiAl sample shows a complex microstructure which is composed of near-equiaxed gamma grains embedded with long-range ordered (LRO) L1(2) domains, various intragranular precipitates including Al2O3, B2, Heusler particles and gamma-TiAl particles and grain boundary precipitates such as sigma. With such a unique microstructure, the samples show remarkably enhanced 0.2% yield strength and significantly improved ultimate tensile strength and strain hardening rates. Precipitates such as Al2O3, Heusler and sigma were found to have acted as effective dislocation motion obstacles. Dislocations tended to cut through the LRO L1(2) domains by forming stacking faults with a number of them intersecting to form immobile Lomer-Cottrell locks which are beneficial for strain hardening.