Cryogenic Treatment of CoCrFeMnNi(NbC) High-Entropy Alloys

Abstract

The effect of cryogenic treatment on the microstructure and mechanical properties of CoCrFeMnNi and CoCrFeMnNi(NbC) high-entropy alloys was investigated during annealing. The heat-treated samples were characterized by optical microscopy, scanning electron microscopy–wavelength-dispersive x-ray spectroscopy, x-ray diffraction technique, differential scanning calorimetry, Vickers hardness testing and tensile testing. The results showed a single-phase FCC crystal structure matrix in both alloys during cryogenic treatment and annealing. Cryogenic treatment altered the recrystallization behavior of CoCrFeMnNi high-entropy alloy, while it did not influence the recrystallization of CoCrFeMnNi(NbC) high-entropy alloy. It was also found that cryogenic treatment changed the precipitation behavior of CoCrFeMnNi(NbC) high-entropy alloy during annealing. In both studied high-entropy alloys, the mechanical testing indicated that the cryogenic treatment can effectively reduce the yield strength of cold-rolled samples after annealing. This was primarily attributed to the effect of cryogenic treatment in enhancing crystalline defects annihilation. Furthermore, the cryogenic treatment increased the ultimate tensile strength of CoCrFeMnNi(NbC). A lager plastic deformation and precipitates were considered as the main reasons for the higher ultimate tensile strength.