Enhanced cryogenic and ambient temperature mechanical properties of CoCuFeMnNi high entropy alloy through controlled heat treatment

Dedicated thermal treatments can improve the mechanical behaviour of high entropy alloys (HEAs) by producing nanostructured microstructures with improved characteristics. Herein, the inherent metastability of an equiatomic CoCuFeMnNi alloy was exploited to induce the formation of secondary phases upon ageing treatment. Advanced characterization techniques, namely high resolution synchrotron X-ray diffraction and aberration corrected scanning transmission electron microscopy, allowed to describe the decomposition of the supersaturated solid solution. Nanometric rounded Cu-rich clusters in the solution-treated alloy and coherent, regularly oriented Cu-rich discs in the peak-aged condition were possibly produced by spinodal decomposition. An almost 100% enhancement of mechanical strength was obtained thanks to the modulation of composition. Moreover, mechanical behaviour at cryogenic temperature was improved by ageing, both in terms of strength and ductility. Plastic deformation took place by dislocation slip, regardless of the testing temperature.