Al_xCoCrFeNi (0.5 < x < 3) high-entropy alloys: from cost-effective synthesis to strengthening via thermomechanical processing

In this study, the cost-effective synthesis, shaping and strengthening through hot and cold rolling of Al_xCoCrFeNi (0.5 < x < 3) high-entropy alloys was investigated using an integrated processing method for the first time in the literature that involved non-centrifugal self-propagating high-temperature synthesis (SHS) followed by suction-casting. Compositions of the master alloys were well-controlled by virtue of thermochemical simulations (CALPHAD) and were acceptable for secondary processes. The FCC-based Al_0.5CoCrFeNi alloy exhibited the highest hot deformability (36%) at 1000°C among the all alloys resulting in a 109% increase in hardness, with respect to its as-cast state. It was possible to obtain Al_0.5CoCrFeNi plates with improved hardness (42%) compared to the SHS master alloy, with substantial area reduction (131%) through the cold-rolling route. Despite the calculated phase diagram suggesting no sigma formation around 1000°C, the hardness increase in the hot rolling process caused by the synergistic precipitation of BCC-B2 and σ phases via hot deformation. It was concluded that the FCC-based Al_0.5CoCrFeNi alloy can be successfully manufactured from oxides to final or semi-final products for applications requiring various thicknesses and improved mechanical properties through static or dynamic precipitation hardening by the selection of cold and hot rolling routes, respectively.