A multicomponentcoating has been developedto protect Nb-base alloys from high-temperatureoxidation. A solid solution of molybdenumand tungsten disilicide, (Mo,W)Si 2 provided the best results. This alloy compositionwas shown to support a slow-growingprotectivesilica scale in service. Germanium additionsmade during the coating process helped to improvethe cyclic oxidation resistanceby increasingthe thermal expansioncoefficientof the silica scale. Germanium also helped to avoid "pesting"(acceleratedlow temperatureoxidation)by providing better sealant coverage at low temperatures. The results of cyclic oxidationtests performedon coated Nb coupons at 900°C, 1370°C, and 1540oC in air are presented. The coated Nb successfullypassed 200 one-hour cyclic oxidationtests at 1370oC and 60-h at 1540°C. Neither generalized acceleratedlow temperatureoxidation or "pest" oxidation occurred when the coatings were exposed to isothermalconditions of up to 200-h in air in the temperaturerange 500-700oC.
A multicomponent diffusion coating has been developed to protect Nb-base alloys from high-temperature environmental attack. A solid solution of molybdenum and tungsten disilicide, (Mo,W)Si2, constituted the primary coating layer which supported a slow-growing protective silica scale in service. Germanium additions were made during the coating process to improve the cyclic oxidation resistance by increasing the thermal expansion coefficient of the vitreous silica film formed and to avoid pesting by decreasing the viscosity of the protective film. The development of the halideactivated pack cementation coating process to produce this (Mo,W)(Si,Ge)2 coating on Nb-base alloys is described. The results of cyclic oxidation for coupons coated under different conditions in air at 1370~ are presented. Many coupons have successfully passed 200 1 h cyclic oxidation tests at 1370~ with weight-gain values in the range of 1.2 to 1.6 mg/cm 2.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.102.42.98 Downloaded on 2014-11-02 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.102.42.98 Downloaded on 2014-11-02 to IP
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.