The Characteristic and Thermodynamics/Kinetics of Martensitic Transformation in Fe₅₀Mn₃₀Co₁₀Cr₁₀ High‐Entropy Alloy during Deformation/Heat Treatment

Abstract

The characteristic of martensitic transformation in the Fe50Mn30Co10Cr10 high‐entropy alloy during deformation/heat treatment is analyzed with optical microscopy (OM) and X‐ray diffraction (XRD). The mechanism of martensitic transformation is first quantitatively analyzed based on Olson–Cohen thermodynamics calculation and kinetics calculation of critical stresses required for martensitic transformation, twinning, and dislocation slip. The content of martensite in the HR (the as‐cast sample hot rolled at 1173 K and air quenched) sample is decreased, whereas in the HRQ (the HR sample annealed at 1273 K for 2 h and water quenched) sample is increased. The content of martensite in the CR (the HRQ sample cold rolled with 40% deformation) sample is significantly increased, whereas in the CRQ (the CR sample annealed at 1173 K for 5 min and water quenched) sample is decreased. Thermodynamics and kinetics calculations show that the martensitic transformation is inhibited at high temperature due to its positive martensitic transformation free energy difference (ΔGγ→ε), high stacking fault energy, and the highest critical stress required for martensitic transformation compared with twinning and dislocation slip. Martensitic transformation is promoted by deformation at low temperature due to its negative ΔGγ→ε, low stacking fault energy, and the lowest critical stress.

Structure and cryogenic mechanical properties of severely deformed nonequiatomic alloys of Fe–Mn–Co–Cr system

“…These studies show that in many nonequiatomic HEAs, as well as in medium entropy equiatomic alloys (MEAs) with less than 5 components such as CoNiCr, Fe 40 Mn 40 Co 10 Cr 10 , Fe 50 Mn 30 Co 10 Cr 10 , and a number of others, high physical and mechanical properties are observed. During deformation, especially at low temperatures, several deformation mechanisms operate in these alloys, such as twinning and phase transformations, known as the TWIP and TRIP mechanisms [32][33][34]. The effect of TWIP and TRIP mechanisms in coarse-grained HEAs Fe 40 Mn 40 Co 10 Cr 10 , Fe 50 Mn 30 Co 10 Cr 10 in a wide temperature range (300-0.5 K) was first studied in our early work [35][36][37].…”