Improvement of the corrosion performance of a cold-rolled Co40Cr20Ni30Al5Ti5 high-entropy alloy by adjusting annealing treatments

High-entropy alloys (HEAs) are expected to possess various excellent properties due to their vast composition design space and unique core effects. Annealing treatments after cold rolling are widely discussed as an effective means to improve the overall performance of the alloy. Nevertheless, the effect of annealing treatments on the corrosion resistance of cold-deformed alloys is still somewhat controversial. Therefore, cold rolling and annealing at different temperatures are performed on the Co40Cr20Ni30Al5Ti5 high-entropy alloy to investigate the effect of annealing temperature on its corrosion behavior. The annealing temperature range covers all stages of the HEA recovery-recrystallization-grain growth (in 50 °C gradients). The experimental results show that the HEA recrystallization is fundamentally complete at 850 °C and fully austenitized at 1050 °C. The best corrosion resistance performance is observed at 850 °C, with the lowest corrosion current density (ipass) and the lightest pitting in full immersion experiments. In addition, excellent passivation properties, such as the lowest steady-state current density iss and highest passivation film growth rate, are achieved at 850 °C. Further analyses of the growth films also show that the passivation films formed at 850 °C are thicker and uniform, and additionally have the highest Cr2O3 content. Accordingly, the effects of annealing temperature on HEA corrosion resistance and passivation behavior are discussed. The superior corrosion resistance and passivation behavior at 850 °C are attributed to the coupling of grain size and passivation film composition. The current findings might guide the optimized design of future cold-deformed alloys for better corrosion resistance.