Morphology, structure and formation mechanism of silicide coating by pack cementation process
(1.湖南省长沙市中南大学材料科学与工程学院2.School of Materials Science and Engineering, Central South University, Changsha 410083, China;Key Laboratory of Nonferrous Metal Materials Science and Engineering,Ministry of Education, Central South University, Changsha 410083, China3.College of Materials Science and Engineering, Central South University, Changsha 410083, China4.School of Materials Science and Engineering, Central South University, Changsha 410083, China)
Abstract: 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.
Key words: niobium based alloy; pack cementation; silicide coating; formative mechanism