Ultrahigh strength induced by multiple heterostructures in a FeMnCoCrN high-entropy alloy fabricated by powder metallurgy technique

Recently, high-entropy alloys (HEAs) in which the face-centered cubic (fcc) structure is dominant have attracted great attention due to their excellent ductility and good fracture toughness. However, the room-temperature yield strength of those alloys is usually low, which can not meet the demand of engineering applications. In addition, grain refinement in HEAs is limited, thus ultrahigh strength can not be achieved through grain boundary strengthening. In this study, a heavily N-doped (5 at.%) FeMnCoCr HEA with multiple heterostructures was prepared by the mechanical alloying (MA) method combined with spark plasma sintering (SPS). It consisted of recrystallized grains with the sizes ranging from submicron to micron and uniformly dispersed nano-scale nitrides and oxides. The N-doped alloy sintered at 900 C exhibited a high compressive yield strength up to 1960 MPa at room temperature, which was-7.8 times stronger than that of the as-cast FeMnCoCr base alloy. In addition, under compression the soft and the hard domains within the inhomogeneous microstructures accommodated deformation with each other. This promoted continuous activation of dislocation slip and interactions between dislocations and stacking faults, leading to a satisfactory fracture strain of 21% and some work hardening ability for the alloy.