Effect of Compositional Tuning of Co Content on Microstructure Evolution and Property Optimization in CrFeNiAlSi...

To improve the comprehensive properties of CrFeNiAlSi HEA, CrFeNiAlSiCo _x (x = 0.3, 0.6, 0.9, 1.2, molar ratio) high-entropy alloys (HEAs) with a multiphase structure were designed and fabricated by adding Co element. The phase compositions of the alloys were theoretically predicted based on the solid solution phase formation criteria. Combined with XRD, SEM, and EDS, the effects of Co content on the phase structure and microstructure evolution of the alloys were systematically investigated, and the hardness, wear resistance, corrosion resistance, and high-temperature oxidation resistance at 800 °C of the alloys were evaluated. The results show that the HEA phase prediction results agree well with the experimental characterization, and all CrFeNiAlSiCo _x HEAs exhibit a multiphase structure consisting of BCC and Cr₃Si phases. All alloys display a dendritic morphology, and the grain size is gradually refined with increasing Co content. The grain boundary regions are enriched with Si, the intragranular region consists of the AlNi phase, and the Co element is uniformly distributed across the grain boundaries and intragranular regions without obvious segregation. In terms of mechanical properties, the Co_0.9 HEA exhibited the optimal hardness (1138.7 HV) and wear resistance (wear loss per unit area of 5.28 mg·cm^-2). Regarding corrosion and oxidation performance, there is an optimal value for the effect of Co content: the Co_1.2 HEA exhibited the lowest annual corrosion rate (0.014 mm/a) in a 3.5 wt % NaCl solution and the minimum weight gain (0.700 mg·cm^-2) after oxidation in static air at 800 °C for 100 h, demonstrating the best corrosion resistance and high-temperature oxidation resistance.