A novel medium entropy alloy based on iron-manganese-aluminum-nickel: influence of boron addition on phase formation, microstructure, and mechanical properties

Abstract

A novel Medium Entropy Alloy (MEA) based on Fe–Mn–Al–Ni has been designed adopting High Entropy Alloys’ (HEAs) phase formation rules, and the effects of minor boron addition on phase content and mechanical properties have been separately investigated. Boron-free Fe(52.71-x)Mn31.11Al5.09Ni11.08Bx (x = 0, 0.05, 0.2, 0.5, 0.7 wt%) MEA showed a single face-centered cubic (FCC) structure. XRD results indicated that with 0.05 and 0.2 wt% boron addition the system maintains its single-phase structure. Further boron addition led to the formation of metal boride intermetallics by the volume fractions of 4.6 and 6.1% of Fe2B intermetallic phase in as-cast and 2.7 and 5.4% in Deformed and Heat-treated (D&H) samples according to Rietveld analysis for 0.5 and 0.7 wt% boron doped alloys, respectively. Boron addition had a positive effect on grain size reduction of the system where just by 0.05 wt% boron addition the grain size has been almost halved compared to boron free as-cast sample. Moreover, it was observed that as the boron level increases, the hardness value increases. With in the all samples subjected to thermomechanical process, 0.7wt % boron doped alloy showed the best yield strength (increasing by ∼50%, from 151 MPa to 222.5 MPa) and ultimate tensile strength (increasing by ∼15%, from 476 MPa to 543 MPa) compared to undoped MEA at comparable ductility (ε > 60%).