Towards the best strength, ductility, and toughness combination: High entropy alloys are excellent, stainless steels are exceptional

Remarkable mechanical properties have been reported for CoCrFeMnNi-based high entropy alloys (HEAs) in recent literature, making these HEAs potentially attractive candidates for future cryogenic applications. However, the damage and fracture behaviour of HEAs is not fully understood yet, especially at low temperature. Here, the mechanical behaviour and fracture resistance of CoCrFeMnNi and CoCrNi sheets are investigated at room and cryogenic temperatures and compared to more conventional alloys. Very good properties were confirmed for HEAs, but outperformed by stainless steels under similar conditions, in terms of ductility, strength, and fracture toughness combination. Exceptional low temperature fracture energy up to 2500 kJ/m2 was found for stainless steels compared to 700 kJ/m2 for HEAs. A predictive model was developed and validated experimentally in order to connect the thin sheet fracture toughness to the strain hardening capacity through separating the necking and damage work spent in the fracture process zone, providing guidelines for further optimization.