Synergistic Effects of Al Content and Cold Rolling on the Microstructural Evolution and Annealing Behavior of FeCoCrNi-Based High-Entropy Alloys

This study investigates the effect of cold rolling and subsequent annealing on the microstructural evolution and hardness of Fe16Co28Cr40-xNi16Alx (x = 8, 10) high-entropy alloys (HEAs). The initial state alloys were subjected to 90% cold rolling followed by annealing at 800 °C for 15 and 30 min. Results indicate that both initial state alloys exhibit a typical face-centered cubic (FCC) dendritic morphology, with the higher Al content in the Al10 alloy promoting greater elemental segregation and yielding a higher initial hardness of 213.1 HV compared to 192.9 HV for the Al8 alloy. During 90% cold rolling, the dendrites of the Al8 alloy undergo severe fragmentation and refinement, reducing the dendritic feature size to 2.0 μm and leading to an 82% surge in hardness to 351.6 HV. Conversely, the Al10 alloy maintains continuously elongated dendritic bands due to higher deformation resistance, reaching a hardness of 334.0 HV. During subsequent annealing at 800 °C, the microstructural evolution pathways diverge. The Al8 alloy predominantly experiences recovery softening accompanied by structural dispersion, whereas the Al10 alloy exhibits continuous hardening due to substantial solid solution strengthening and high microstructural stability. These findings demonstrate that altering the Al content fundamentally shifts the initial deformation mode. Cold rolling plays a critical role in fragmenting the initial dendritic structure and in redistributing the solute-rich segregation domains to a finer scale, while driving substantial work hardening. Subsequent annealing governs the critical balance between recovery softening and structurally driven continuous hardening, highlighting the synergy of composition and processing in tuning the stability and performance of HEAs.