Aluminide and silicide diffusion coatings by pack cementation for Nb-Ti-Al alloy

Halide activated pack cementation technique was successfully used to elaborate protective coatings, based on silicon- or aluminum-rich intermetallic compounds, for a Nb-Ti-Al alloy. Thermodynamic computations showed that growth mechanism of coating involves different chemical reactions. The substrate shows a poor behavior in thermal oxidation with the formation of non-protective oxides and high solubility of oxygen in its microstructure. The effectiveness of the deposited MAl3 and MSi2 coatings to protect the substrate was demonstrated. Reliability and high oxidation resistance of these diffusion coatings are promoted by their good adherence to the substrate, capability to accommodate thermo-mechanical stress and ability to form adherent and compact Al2O3 and SiO2 oxide scales. These oxide scales grow during the oxidation process at 900 and 1000 °C according to very low kinetics as demonstrated by the curves of mass change versus time. The mass changes of the coated substrate with aluminide and silicide were