Development and characterization of a novel high entropy alloy strengthened through concurrent spinodal decomposition and precipitation

Strengthening mechanisms, which are commonly exploited by conventional alloys, can be effectively incorporated in high entropy alloys (HEAs) to improve their mechanical behaviour. In this light, compositional modification of equiatomic HEAs can be pursued in order to obtain specific microstructural features. Herein, a face centred cubic CoCuFeMnNi alloy was modified by the addition of a proper amount of Ti; a dedicated thermal treatment allowed to concurrently activate two different phase formation mechanisms, i.e. precipitation and spinodal decomposition. This resulted in a nanostructured microstructure, characterized by the presence of periodic modulations of Cu content and by nanosized coherent L12 Ni3Ti precipitates. Such microstructure resulted in a more than 100 % increase of yield strength after ageing treatment and allowed to retain a satisfactory ductility. Advanced microstructural characterization, coupled with the application of semi-empirical models allowed to understand the role of each microstructural feature in determining the alloy's mechanical strength.