چكيده به لاتين
Medium-entropy alloys (MEAs), unlike high-entropy alloys (HEAs), are typically multiphase due to their lower entropy values (0.69–1.61 R) and greater instability in the matrix phase. This characteristic allows MEAs to easily transform into multiple phases, potentially enhancing mechanical properties and achieving higher stability. The lack of a requirement to maintain a single-phase structure (as in HEAs) enables these alloys to combine suitable mechanical strength and ductility, making them advantageous for engineering applications and easier and more cost-effective to produce. Additionally, the improved phase stability under high-temperature or corrosive conditions significantly reduces issues related to phase or elemental segregation in MEAs compared to HEAs. In this research, the iron-based medium-entropy alloys Fe50-(CoCrMnNi)50 (single-phase) and Fe50Mn30Co10Cr10 (multiphase) were subjected to hot compression tests at various strain rates and temperatures ranging from 650°C to 850°C. A detailed analysis of the stress-strain curves and microstructural evolution in these two alloys was conducted to determine the hot deformation behavior, dynamic restoration processes, constitutive equations, and deformation mechanisms during high-temperature deformation. Both alloys exhibited discontinuous dynamic recrystallization under hot compression, characterized by necklace structures at grain boundaries. The initial deformation in the single-phase alloy Fe50-(CoCrMnNi)50 resulted in slip, dislocation entanglment, dislocation density increase, and grain boundary migration, showing a behavior similar to recrystallization in conventional alloys. As strain increased, the deformation mechanism in the Fe50-(CoCrMnNi)50 alloy transitioned to grain boundary sliding (instead of secondary recrystallization) at lower Zener-Hollomon parameter values due to matrix phase instability. The activation energy for hot deformation of the medium-entropy alloy Fe50-(CoCrMnNi)50 was calculated to be high (Q = 215.61 kJ/mol), indicating the influence of iron on deformation behavior and the immobility of dislocations and grain boundaries. Moreover, optimal deformation maps based on temperature and strain rate suggest the ideal range is between 750°C and 800°C and a strain rate of 0.0014–0.0037 s⁻¹. In the multiphase medium-entropy alloy Fe50Mn30Co10Cr10, necking onset was delayed compared to conventional alloys under high-temperature deformation, suggesting competition between necking and mechanisms like the formation of HCP martensite and FCC→HCP reverse transformation. In this alloy, deformation is influenced by strain-induced martensitic transformation, twinning, and slip. Optimal deformation maps for the Fe50Mn30Co10Cr10 alloy based on temperature and strain rate suggest the ideal range is 710–750°C and a strain rate of 0.0025–0.0035 s⁻¹. The activation energy for hot deformation of this iron-based medium-entropy alloy was calculated to be very low (Q = 129.89 kJ/mol), indicating the influence of shear mechanisms on the deformation process. Notably, despite not fully conforming to the general behavior of high-temperature deformation, the developed Zener-Hollomon parameters show good agreement with experimental results for both alloys.
