High-Temperature Oxidation Behavior of NiCoCrAlY Coatings Deposited by Laser Cladding on 304 Stainless Steel

To improve the high-temperature resistance of the key hot-end parts of the steam turbine, NiCoCrAlY coatings were deposited on a 304 stainless steel substrate by laser cladding. The microstructure and high-temperature oxidation behavior of the NiCoCrAlY coatings were analyzed. The results showed that the NiCoCrAlY coatings contained γ/γ′ and β phases, and the microstructure was mainly composed of elongated columnar crystals. In addition, after 100 h of oxidation at three different oxidation temperatures (750, 850 and 950 °C), the coatings showed a relatively low oxidation rate, which was approximately a quarter of the oxidation rate of the substrate. At the same time, the protective Cr2O3 scales were formed on the coating surface. When the oxidation temperature was 850 °C, the FeCr2O4 spinel formed and internal oxidation zone appeared, when the oxidation temperature reached 950 °C, the FeCr2O4 spinel gathered in the local area on the surface of the Cr2O3 scale and the internal oxidation was aggravated. In other words, as the oxidation temperature increased, the Fe element in the matrix formed the FeCr2O4 spinel, which accelerated the consumption of Cr element in the coatings and reduced the overall oxidation resistance of the NiCoCrAlY coatings.