GOALI: A Fundamental Investigation of the Design, Processing and Evaluation of a Model, Oxidation Resistant, Functionally-Graded Coating System for Refractory Metals

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9730775 Moore The research program investigates functionally-graded coating systems that incorporate an amorphous diffusion barrier layer. Past research identified a functionally- graded molybdenum-silicon based coating system (MoSi2-SiC), deposited on the refractory metal substrate using physical vapor deposition as a promising processing route. A sufficiently thick, outer layer of MoSi2 can be subsequently applied to the functionally-graded layer using plasma spraying. The earlier research also identified the potential of utilizing MoSi2-SiC composite targets as compared with elemental targets (e.g. Mo, Si, and C). However, a suitable diffusion barrier layer between the MoSi2-SiC functionally-graded coating and the refractory metal substrate must be identified in order to minimize diffusion of silicon and carbon into the refractory (Mo or W) substrate. If this barrier is not used, sub-silicides and carbides of the refractory metals are produced at the coating-substrate interface, resulting in deterioration of oxidation resistance and mechanical properties of the coating system, as well as a reduction in the coating life. A Mo-Si-N-C diffusion barrier has recently been identified that remains amorphous up to 1260C. Thermal cycling of the MoSi2-SiC functionally-graded coating system between the service temperature and room temperature can produce stresses in the coating system. Therefore, finite element modeling will be used to predict the optimized compositional gradient, and coating architecture, i.e. substrate-barrier layer-functionally-graded layer-outer thick kinetic layer, consistent with minimizing the stresses generated, and maintaining oxidation resistance for prolonged times up to 1600C in air. ? Industrial advisors are Mel Jackson (GE Corp. Research and Development) and William Allen (UTRC - East Hartford). These co mpanies have interest in high temperature materials and coatings for materials used in turbine engines. Students spend time in the industrial laboratory research facilities and present their research activities at CSM Center meetings. It is an excellent opportunity for the students to participate in superb industrial materials laboratories in the United States. The MPS OMA Office is co-supporting this GOALI activity. %%% The main objective of this GOALI research program is to explore oxidation-resistant coating systems for refractory metals for application in high temperature, oxidizing environments. The coatings are designed using finite element modeling and deposited by physical vapor deposition using novel MoSi2-SiC or MoSi2-Si3N4 composite targets. The research program is managed in the Advanced Coatings and Surface Engineering Laboratory (ACSEL), an industry- university consortium, at Colorado School of Mines. ***