331 Microstructure Evolution in Thermal Spray Coatings and its relevance in High Temperature Behavior
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概要
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This paper describes a detailed characterization study of the complex layered microstructures of thermal spray coatings. These are being characterized across length scales in order to look at various features such as porosity and phases in coating cross-sections, splat structure, splat interfaces, grain structure within splats, etc. This study incorporates the use of Optical microscopy, SEM & Image analysis for low magnification studies of ceramic and metallic systems and also the use of SEM and TEM for high magnification characterization. It explores and exhibits the necessity and applicability of each of these techniques for understanding the evolution of microstructure during formation of coatings. Porosity in YSZ topcoats is characterized and categorized using Image analysis and results are correlated with more advanced techniques of porosity measurement. The mechanisms of single splat formation and oxidation involved are studied and schematic models are presented to explain the deposit formation of Ni-5Al bond coats in case of different processes such as APS, Wire-arc, HVOF and Cold spray techniques. Having thus examined the microstructural intricacies in topcoat and bond coat systems, this study then explores the sintering and oxidation behavior of the TBC system as a whole. The effects of heat treatment temperature time and environment, and effect of feedstock and bond coat spraying system used, are studied for single splats of PSZ, sprayed onto CoNiCrAlY bond coats. Sintering effects are investigated in single splats rather than thick free-standing deposit to evaluate the role of splat-substrate interaction, thermal mismatch and TGO growth.
- 2005-11-03