Reaction layers structure of silicide coatings on niobium alloys

This paper reports on fused silicide coatings that are used to protect niobium alloys against high temperature oxidation. Quantitative electron microprobe analysis was used to characterize the complex multilayer structure of Si-20w/oFE-20w/oCR fused silicide coating on four niobium containing alloys: niobium, Cb752, WC3009, and Nb-46.5 Ti. The outer coating layer structure on all four alloys was similar, consisting of either two or three phases. The three phase outer coating layer on the niobium, WC3009, and the Nb-Ti substrate alloys was determined to be made of two MSi phases and one MSi2 phase. This outer MSi2 phase contained base alloy elements. Coated samples were compared using cyclic oxidation testing. The fused silicide coating structure and protectiveness were determined to be a function of the base alloy composition