Fabrication of Co-Based Cladding Layer by Microbeam Plasma and Its Corrosion Mechanism to Molten Salt

Corrosion of the molten salts Na₂SO₄ and NaCl has become one of the major factors in the failure of steel components in boilers and engines. In this study, CoNiCrAlY cobalt-based cladding layers with different NiCr-Cr₃C₂ ratios were prepared by microbeam plasma cladding technology. The influence of the NiCr-Cr₃C₂ content on the microstructure, mechanical properties, and molten salt corrosion resistance of CoNiCrAlY was investigated. The CoNiCrAlY with a 25 wt.% NiCr-Cr₃C₂ (NC25) cladding layer possessed the highest microhardness (348.2 HV_0.3) and the smallest coefficient of friction (0.4751), exhibiting great overall mechanical properties. The generation of protective oxides Cr₂O₃, Al₂O₃, and spinel phase (Ni,Co)Cr₂O₄ is promoted by the addition of 25 wt.% NiCr-Cr₃C₂, which significantly reduces the corrosion of the cladding layer, and this effect is much more obvious at 950 °C than that at 750 °C. Furthermore, its corrosion mechanism was clarified. From the findings emerge a viable solution for the design and development of new high-temperature corrosion-resistant coatings.