Synthesis and characterisation of pack cemented aluminide coatings on metals

The exposition of metallic materials to high temperature environments leads to their corrosion because of oxidation or sulphidation. One way to protect such materials is to produce an Al2O3 layer which needs to be continuous enough to limit diffusion of oxygen or metallic elements, and withstand this corrosion. Since a few years, it has been proved that aluminide compounds are one of the most effective materials to achieve this goal. Indeed, they possess sufficient Al and many beneficial mechanical properties when exposed to high temperature conditions to make possible the formation of a protective Al2O3 scale. This study is aimed at the elaboration of iron, nickel and molybdenum aluminides by modification of the surface of the base materials by a pack cementation process. The as-cemented alloys were analysed by means of SEM coupled with EDX and by XRD. Cross-section examinations showed, in each case, a progressive diffusion of aluminium through the substrates. The diffusion thickness layer was more or less important depending on the base material and on the coating conditions. (Substrates: Fe-30Cr, Fe, Ni, Mo.)