Pack cementation coatings for degradation control of refractory high entropy alloys

Refractory high-entropy alloys offer high-temperature strength but degrade rapidly in oxidizing environments. This Review examines halide-activated pack cementation as a surface-design strategy for controlling oxidation-driven degradation. We connect coating growth, silicide and aluminide formation, protective-scale chemistry and failure modes, and propose design criteria for coating architectures that retain protective reservoirs while avoiding brittle reaction zones.