Substrate controlled degradation rate of protective SiAlN coating via mitigating interfacial reaction

The degradation rates of protective SiAlN coatings (0.9 mu m thick) on pure Ti, Ti6Al4V, and Timetal 834 alloys in air at 800 degrees C were investigated and compared. The SiAlN coating on pure Ti was depleted and then formed a thin oxide scale after exposure of 50 h, whereas a 0.6 mu m thick remnant SiAlN coating without any signs of oxidation was observed on Timetal 834. Interfacial reactions between SiAlN coatings and different substrates caused depletion of SiAlN, thereby determining the degradation rates of SiAlN coatings. The non-reactive alloying elements Sn and Al in Timetal 834 alloy could retard such interfacial reactions, thereby impeding coating degradation.