An experimental and computational framework to investigate the thermal cycling approach for strengthening low SFE FeMnNi medium entropy alloy

Thermal cycling treatment was adopted for the microstructural engineering of a ternary equiatomic FeMnNi medium entropy alloy (MEA) for achieving different strength-ductility combinations using instrumented indentation and electron backscatter diffraction. A computational model based on cellular automata that accounts for the thermodynamic and kinetic aspects of microstructural evolution was used for predicting recrystallization and grain growth during conventional isothermal single-step and cyclic annealing. The current investigation suggests that an equivalent isotemporal thermal cycling treatment produces a recrystallized microstructure of lower average grain size with a more uniform grain size distribution and a lower variance as a result of inhibition of grain growth. Superior strength-ductility combinations are obtained for all the thermal cycling samples compared to single-step annealed samples. The thermally cycled recrystallized sample demonstrated a yield strength of 561 +/- 10 MPa with ductility of 46.7 +/- 3.5% against the isothermally recrystallized sample with a yield strength of 406 +/- 11 MPa and elongation up to 35.1 +/- 5.2%. Thus, the present study demonstrates that thermal cycling treatment provides superior control over the microstructure and optimum combination of strength and ductility in FeMnNi MEA.

Automated summary

The microstructure of a ternary equiatomic FeMnNi medium entropy alloy (MEA) was engineered using thermal cycling treatment, resulting in superior control over the microstructure and an optimum combination of strength and ductility. The thermal cycling treatment produced a recrystallized microstructure with lower average grain size, more uniform grain size distribution, and inhibition of grain growth. This resulted in superior strength-ductility combinations compared to single-step annealing samples.