On the Effect of Heat-Treatments in a PBF-LB/M Processed FeCrMnNi Medium-Entropy Alloy

FeCrMnNi-based alloys, derived from the well-known Cantor high-entropy alloy, have attracted increasing attention due to their excellent strength–ductility balance. Additively manufactured FeCrMnNi variants are characterized by superior hardness compared to their conventionally processed counterparts. In the present study an optimized composition of the FeCrMnNi medium-entropy alloy was additively manufactured via laser-based powder bed fusion and subsequently subjected to systematic heat treatments. CALPHAD simulations were applied to select the specific composition and post-processing heat treatment conditions, where the latter aimed at promoting the evolution of a dual-phase microstructure. Experimental characterization included X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction, as well as Vickers hardness and tensile testing. A microstructure could be established dominated by a face-centered cubic (FCC) phase with minor fractions of a secondary phase in the non-treated condition. The evolution of an additional body-centered cubic (BCC) phase upon heat treatment at and above 700 °C was observed. The emerging BCC phase as well as increasing fractions of the secondary phase were accompanied by significantly increased hardness and strength, surpassing the literature values of similar compositions. However, a heat treatment at 1000 °C resulted in recrystallization and an increase in grain size, while the decreasing fraction of the secondary phase eventually led to a reduction in strength. These findings underscore the combined potential of composition optimization and targeted post-processing to enhance the mechanical performance of additively manufactured FeCrMnNi alloys.