Microstructure and properties of CoCrFeNi-based multi-principal element alloys containing C and Sc

Abstract A series of novel CoCrFeNi-based high-entropy alloys containing Sc and C were designed. These HEAs exhibited hardness, fracture toughness and wear resistance comparable or better than a range of selected benchmark systems. Microstructurally, we observed composite microstructures comprising variously a Sc-rich intermetallic phase, a sigma phase and an FCC solid solution phase within which precipitated M 23 C 6 carbides. The Sc-rich intermetallic phase possessed a stoichiometry close to (Co, M) 2 (Sc, M), where M = Ni and Fe. As the carbon content increased, the hardness levels ‘softened’ from 799 VHN (C-free) to 674 VHN (C = 4 at.%), though the fracture toughness was increased ~ 112%. At the same time, the specific wear rate was enhanced from 0.33 × 10 −3 to 0.14 × 10 −3 mm 3 ·(N m) −1 . The effectiveness of these microstructures in balancing high hardness, crack deflection and a relatively low wear rate was attributed to the enhanced stability of the FCC solid phase as the C content was increased. Graphical abstract