Morphology, structure and formation mechanism of silicide coating by pack cementation process

The MoSi2 coating on C103 niobium based alloy was prepared by pack cementation method. The formative mechanism, morphology and structure of coating were investigated. The silicide coating was formed by reactive diffusion obeying parabolic rule during pack cementation process. It is found that the composite structural coating is composed of three inferior layers as follows. The main layer is composed of MoSi2, the two phases' transitional layer consists of NbSi2 and a few Nb5Si3 and the diffuse layer is composed of Nb5Si3. The dense amorphous glass layer formed on the surface at high temperature oxidation circumstance can effectively prevent the diffusion of oxygen into coating.