Boro-aluminising of P91 steel by pack cementation for protection against steam oxidation

High performance alloys are often the materials used for various components exposed to high temperature environments. In many cases, protective coatings are applied in these alloys, providing higher corrosion and oxidation resistance, compared to the base material. This study investigates the feasibility to apply boro-aluminising treatment on P91 steel by pack cementation process, to increase the steel high temperature properties in oxidising and corrosive environments. Packs activated by AlCl₃, NH₄Cl and KBF₄ were used to carry out the coating deposition at a temperature of 715°C for 6 h. The coating formed was analysed by means of SEM and XRD, and the compounds formed were identified. Cyclic steam oxidation for a total of 1008 h at 650°C revealed an oxide scale of 50 μm for the uncoated P91 steel, while the coated steel shows practically no oxidation effect.