Influence of alloying and aging treatment on the strain hardening behavior of non-equiatomic CoCrFeNi high entropy alloy

The objective of the study was to investigate the work hardening behavior of Al_xCo_1.5CrFeNi_1.5Ti_y (where sum of x and y is 0.5, in atomic ratio and x = 0, 0.2, 0.3, 0.5) high entropy alloys (HEAs) in solutionized and peak-aged conditions. Work hardening behaviour was mainly driven by L1₂ and B2 precipitate formation, during aging, and the ease of stacking fault (SF) formation with varying Ti/Al concentrations. Increasing Ti concentration was found to decrease stacking fault energy (SFE), promoting SF formation and further enhanced work hardening. B2 precipitates contributed to Orowan looping-induced hardening, while L1₂ precipitates induced hardening through precipitate shearing via partial dislocations. Addition of Ti into the AlCoCrFeNi system induced a transition in the deformation mechanism from wavy slip to planar slip. Ordered domains formed during aging facilitate SF generation, resulting in higher work hardening rates. In addition, Taylor lattice-type deformation substructures were observed in the solutionized condition of Ti-containing alloys and were absent in their aged counterparts because precipitation facilitates the easy formation of SFs and hence decreases the propensity of Taylor lattices. Present study enhances the understanding of work hardening in various HEA compositions, aiding in the optimization of alloy design for structural materials.