Al-Mn CVD-FBR protective coatings for hot corrosion application

Abstract Ferritic steels are usually used in boiler or supercritical steam turbines which operate at temperatures between 600 and 650 °C under pressure. Protective coatings are often applied in order to increase their oxidation resistance and protect them against degradation. In this study, new Al–Mn protective coatings were deposited by CVD-FBR on two ferritic steels (P-92 and HCM12). The initial process parameters were optimized by thermodynamic calculations using Thermo-Calc software. Then, those parameters were used in the experimental procedure to obtain Al–Mn coatings at low temperature and atmospheric pressure. Co-deposition was achieved at moderate temperatures in order to maintain the substrates' mechanical properties. The coatings' microstructure and phase constitution was characterized. Fe–Al intermetallic coatings containing Cr and Mn were obtained. The phase constitution is discussed with reference to the Fe–Al–Mn ternary phase diagram. The effect of diffusion heat treatment on the phase transformations was investigated.