摘要
Three non-equimolar CrFeMoNi medium entropy alloys were designed using the new PHACOMP method to suppress σ phase precipitation and improve corrosion resistance. The alloys were produced by vacuum arc melting followed by homogenization at 1200 °C for 6 h under argon atmosphere. All alloys exhibited single phase FCC structures and demonstrated superior corrosion resistance compared to commercial Hastelloy C276. However, the inherent softness of single phase FCC structures limits their mechanical strength. To address this, thermomechanical grain refinement was applied to the Cr25Fe10Mo10Ni55 alloy via rapid annealing at 1050 °C for 5 min, reducing the grain size from over 500 μm to approximately 35 μm and increasing hardness from 158 HV to 187 HV. As a result of grain refinement, the yield strength and ultimate tensile strength increased to 339 MPa and 809 MPa, representing 1.4 and 1.7 times improvements over the homogenized state, while maintaining a high elongation of 55.8 %. In terms of corrosion behavior, the border passivation window of the fine grained Cr25Fe10Mo10Ni55 alloy, which increased by 169 mV, is due to enhanced grain boundary diffusion, which accelerates the formation of stable Cr2O3 passive films. This leads to improved pitting corrosion resistance. In summary, the fine grained Cr25Fe10Mo10Ni55 alloy, achieves a synergistic enhancement in mechanical strength and corrosion resistance, outperforming Hastelloy C276 in both aspects.