An optimal grain boundary engineering approach to improving the mechanical properties of FeCoCrNi high-entropy alloys at different temperatures

The influence of grain boundary engineering (GBE) on the mechanical properties of FeCoCrNi high-entropy alloy (HEA) at different temperatures was systematically examined. An optimal GBE process, namely cold rolling (with 5 % reduction) followed by annealing (at 900 °C for 4 h), was ascertained to markedly modify the grain boundary character distribution (GBCD) in the alloy, and significantly increase the fraction of special boundaries (Σ3-Σ29) to as high as 82.4 %, and meanwhile, the connectivity of random high-angle grain boundaries (RHAGBs) has been effectively disrupted. Such a modified GBCD leads to an improvement in room-temperature tensile ductility without loss of strength, but to a simultaneous enhancement in strength and ductility at high temperatures (600 °C–800 °C). The improved properties result mainly from the inducement of abundant Σ3 boundaries that effectively inhibit intergranular crack initiation and propagation during plastic deformation. Also, the GBE process optimizes deformation uniformity, mitigates dynamic recovery and recrystallization and suppresses dynamic strain aging at high temperatures, further facilitating more stable and homogeneous plastic deformation. This study has offered a detailed perspective on how GBE affects the plastic deformation and damage behavior of FeCoCrNi HEA at different temperatures, thus providing a novel pathway to improve the mechanical properties of HEA especially at high temperatures.