Thermally stable laser cladded CoCrCuFeNi high-entropy alloy coating with low stacking fault energy

The application of high-entropy alloys (HEAs) as coating materials has become an active research topic recently. Here an fcc structured CoCrCuFeNi HEA coating with a thickness of ∼1.2 mm was laser cladded onto a Q235 steel. The alloy coating possessed an excellent thermal stability in that no phase transformations occurred up to 1000 °C (0.86Tm), and the dendritic morphology of the as-solidified microstructure could be kept to higher than 750 °C (0.7Tm). After annealing the as-solidified coating at 750 °C for 5 h, the lattice distortion in the rapidly solidified alloy was reduced, resulting in a moderate decrease of both the hardness and electric resistivity. Interestingly, profuse stacking faults ribbons were observed in the dendritic region of the alloy after annealing, driven by the thermal stress. This phenomenon provided a direct experimental evidence of the low stacking fault energy in HEAs. The thermodynamic origin of the thermal stability for HEAs was proposed.