Oxidation behaviour of microwave hybrid heating processed CoCrNiTiMo high entropy alloy cladding

CoCrNiTiMo high entropy alloy (HEA) cladding is developed over SA213 T91 steel substrate through a microwave hybrid heating process. The mechanical and microstructural properties of CoCrNiTiMo HEA cladding are analysed. The average thickness of the fabricated clad is 826.43 μm. The cyclic oxidation tests of the cladded and uncladded samples are conducted for 30 cycles of 1 h of heating at 800 °C and 20 min of cooling at room temperature. After completing 30 cycles of oxidation tests, the uncladded specimen exhibited a weight gain of 13.19 mg/cm², whereas the HEA-cladded counterpart showed a comparatively lower weight gain of 8.70 mg/cm². This substantial difference indicates that the HEA cladding reduced the oxidation rate by approximately 34 % compared to the uncladded sample. The XRD analysis revealed the formation of Ni, Co, Cr - rich FCC phase and Cr, Mo, Ti - rich BCC phase in the cladded sample. A continuous TiO₂ layer is also observed on the oxidised cladding specimen surface. The cladded sample showed better oxidation resistance than uncladded T91 steel due to the formation of the protective NiO, NiCr₂O₄, CoCr₂O₄, and Ni₃TiO₅ oxides and spinel.