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Title:: Preparation Technologies and Modified Silicide Oxidation-resistant Coatings of Nb-Si Based Ultrahigh Temperature Alloy

Author(s):: GUO Xiping; State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China

Abstract:: Nb-Si based ultrahigh temperature alloys possess higher melting points, relatively lower densities and attractive high temperature strength, and therefore, they have been expected to be employed in the temperature range of 1200—1450℃. However, their oxidation resistant performance has not been good enough for the actual application in oxidizing environments. In this paper, the composition, preparation technologies and the silicide oxidation-resistant coatings of the alloys have been introduced. Several methods can be adopted to prepare the alloys, such as vacuum arc melting, directional solidification, powder metallurgy, evaporate deposition, shock synthesis, and induction skull melting. Many NbSi2-type oxidation-resistant coatings modified with single or multi-elements including Al, Y, Cr, B, Ce, Zr and Ge have been developed for the alloys, and some of them exhibit excellent protection performance for the alloys and can endure isothermal oxidation at 1250-1350℃ for more than 200 h or cyclic oxidation at 1250℃-room temperature for more than 100 cycles. The addition of Al in the coatings has a significant effect on the structure of the scales formed on the coatings upon oxidation. The existence of a suitable content of Al in the coatings could promote the formation of SiO2 preferentially on the surface of the (Nb,X)Si2 outer layer of the coatings, and thus forming a dense and compact scale mainly consisting of SiO2?Al2O3.