Morphology of composite coatings formed on Mo1 substrate using hot-dip aluminising and micro-arc oxidation techniques

A hot-dip aluminised layer was prepared on a Mo1 substrate and the obtained layer was oxidised in situ by a micro-arc oxidation (MAO) technique to form an oxide ceramic coating. The obtained hot-dip aluminised layer had a two-layer structure overall: the outer layer was a pure aluminium layer, and the inner layer was a diffusion layer. The hot-dip aluminising temperature directly influenced the structure and phase composition of the obtained diffusion layer. The diffusion layer of the hot-dip aluminised layer at 710 °C was divided into three layers. The inner, intermediate, and outer layers were mainly composed of Al₈Mo₃, Al₄Mo, and Al₁₂Mo phases, respectively. The diffusion layer of the hot-dip aluminised layer at 750 °C was divided into two layers: the inner layer was mainly composed of an Al₈Mo₃ phase, and the outer layer of Al₄Mo. After the hot-dip aluminised layer was treated by MAO, a three-layer coating was obtained. The outer layer was a ceramic one obtained by MAO, which was mainly composed of Al₂O₃, mullite, and unoxidized aluminium. The middle one was pure aluminium obtained by hot-dip aluminising and without MAO. The inner layer was an Al–Mo diffusion layer.