Production and development of aluminide coatings by chemical vapor deposition on nickel based superalloys for turbine engine applications

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2017
Ertürk, Umutcan
Diffusion coatings including aluminide coatings are utilized to improve the high temperature oxidation and corrosion resistance of turbine blades. Through the advancement in the aluminizing methods, higher purity and more homogeneously distributed coatings have been realized. The chemical vapor deposition (CVD) is the most advanced technique utilized for aluminizing process. The versatility of CVD provides a large possibility to control process variables such as temperature, pressure, gas flows and ratios, and aluminum activity. However, the main challenge of CVD method is optimizing the process parameters to obtain high growth rate and outer layer/interdiffusion zone (IDZ) ratio while satisfying required coating microstructure and composition. In addition, improvement in the durability of aluminide coating is also an important design criterion to extend the lifetime of turbine blades which could be achieved by the addition of reactive or alloying elements to the coating. In this dissertation, production of aluminide coatings by CVD was investigated to effectively increase growth rate and outer coating layer/IDZ ratio by optimizing the process variables. The influence of temperature, pressure, chlorinator temperature, gas flows and ratios, aluminum activity, and process time were studied on the formation of aluminide coating by univariate experimental analysis. Also, the effect of substrate properties, such as surface roughness, composition, and sample thickness was separately studied. Moreover, co-deposition of reactive (Zr, Hf, Y) and alloying (Cr, Co) elements were investigated to incorporate ternary elements to aluminide coating in desired concentration and distribution. Additionally, the impact of these ternary elements on the hot corrosion behavior of aluminide coatings was evaluated by isothermal hot corrosion test to extend the life time of turbine blades.  
Citation Formats
U. Ertürk, “Production and development of aluminide coatings by chemical vapor deposition on nickel based superalloys for turbine engine applications,” M.S. - Master of Science, Middle East Technical University, 2017.