Preparation of alumina/aluminide coatings on molybdenum metal substrates, and protection performance evaluation utilizing a DZ40M superalloy casting test

Alumina/aluminide coatings were prepared on pure molybdenum substrates by pack cementation and subsequent pre-oxidation treatments in order to protect the underlying molybdenum cores from oxidation, and as well as to molten metal corrosion during the casting of superalloys. The microstructure of the aluminide coatings formed at different aluminizing parameters (time, temperature, and pack chemistry) and the evolution of the corresponding coatings during the pre-oxidation treatments were systematically investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and electron backscatter diffraction (EBSD). A proper coating system defined by the experiments mentioned above is composed of four layers (α-Al2O3, AlMo3, Al8Mo3, and AlMo3) and the multilayer has total thickness < 50 μm. A casting test utilizing DZ40M superalloy demonstrated that the selected coating system showed significant oxidation-resistant and corrosion-resistant capacities.