High Temperature Oxidation Resistance of Silicide Coatings on Nb/NbCr2 Alloy

Silicide coatings on Nb/NbCr2 alloy were prepared by pack cementation method. The oxidation behavior of the bare- and coated- alloy was examined by isothermal test at 1250 ℃ in static air.The results show that the silicide coatings are composed of(Nb, Cr)Si2and(Cr, Nb)Si2phases. There exist a transitional layer of(Nb, Cr)5Si3in between the main coating and substrate. The coating growth kinetics at 1250℃ fits to parabolic law. The oxidation of Nb/NbCr2 alloy resulted in alternate layers of Nb2O5 and Cr Nb O4 with porous structure, which was wrinkling even spalling off after oxidation. The scale formed on the silicide coating after oxidation at 1250℃ was mainly composed of Si O2 and Cr Nb O4. The scale was relatively dense and had a good bond with the residual coating, thus showing an excellent oxidation resistance.