Elucidating the tensile work hardening behaviour of precipitate containing Al_0.3Co_1.5CrFeNi_1.5Ti_0.2 high entropy alloy

A significant amount of work has been performed, since the last decade, on designing novel high entropy alloy (HEA) compositions. However, the effort on concluding a universal mechanism on the strain hardening behavior of these alloys with precipitates is limited. The current study is designed with an aim to comprehend the mechanical behavior of Al_0.3Co_1.5CrFeNi_1.5Ti_0.2 HEA in solution treated and aged conditions. The results show that the peak aged condition of sample contains two types of precipitates – B2 and L1₂ (γ′) of approximately 800 nm and 40 nm size, respectively. They are found to be responsible for a significant increase in strength in aged samples than solution treated ones. Deformation was found to occur mainly by planar slip on the {111} primary slip planes. Noticeable strain hardening behavior was attributed to the formation of stacking faults (SFs) and Lomer-Cottrell (LC) locks, inhibiting the dislocation motion. Numerous paired dislocations formed due to inhibition of slip by the ordered γ′ precipitates, coexist with a few Orowan loops in the peak-aged alloy after deformation. However, the primary strengthening mechanism was found to be the shearing of γ′ precipitates by partial dislocations. Shearing of nanosized γ′ precipitates by partial dislocations is energetically favourable for the system than shearing by full dislocations. Overall, this study enhances the understanding of the precipitation strengthening and strain hardening mechanisms in high entropy alloys.