Cost-effective synthesis and thermomechanical processing of Al_xCoCrFeNiCu_y (x&y=0.5,1) high-entropy alloys

This study investigates the cost-effective synthesis and thermomechanical processing of Al_xCoCrFeNiCu_y (x&y = 0.5,1) high-entropy alloys through cold (CR) and hot rolling (HR). The alloys were synthesized using a thermochemical modelling-assisted aluminothermic non-centrifugal, self-propagating high-temperature synthesis (SHS) method, which is reported for the first time in the literature. Remelting and suction casting were conducted via vacuum arc melting upon the compositional verification through x-ray fluorescence (XRF) and energy dispersive spectroscopy (EDS) analyses. The deformabilities and hardness values of the alloys were correlated with microstructural changes that were analysed through scanning and transmission electron microscopy (SEM, TEM). Among the master alloys, FCC-A1 based Al_0.5CoCrFeNiCu_0.5 (Al0.5Cu0.5) and Al_0.5CoCrFeNiCu (Al0.5Cu1.0) alloys exhibited highest cold deformability (145% and 170%, respectively), accompanied by significant work hardening (114% and 108% increase in hardness, respectively), primarily attributed to dislocation-dislocation interactions. It has been demonstrated for the first time that equiaxed single phase (FCC-A1) Al_0.5CoCrFeNiCu_0.5 high-entropy alloy can be obtained through the CR + annealing. The alloys exhibited reduced hot formability (62% and 85%, respectively) partly due to the formation of Cr-rich sigma phase instead of the Al-Ni rich B2 phase, most notable in the Al0.5Cu0.5 alloy, contrary to the CALPHAD simulations. This led to increased hardness in the alloys through precipitation hardening, achieving similar hardness values as those obtained through cold rolling (CR) with less deformation. The findings support the conclusion that the presented integrated processing strategy offers a cost-efficient means of producing Al_0.5CoCrFeNiCu_y alloys with enhanced mechanical and chemical properties for various engineering applications by the selection of cold and hot rolling routes.