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Processing-Microstructure-Property Relations in Anisotropic Thermal Sprayed Composites

  • Weiguang Chi (a1), Vasudevan Srinivasan (a2), Atin Sharma (a3), Sanjay Sampath (a4) and Richard Gambino (a5)...

Abstract

Thermal spray is a significantly advanced but inherently complex deposition process that involves successive impingement of molten droplets on a substrate to form coating with a ¡°brick-wall¡± layered structure. The anisotropic microstructure of coatings is very sensitive to processing conditions and has significant influence on the properties. This study aims to understand the processing-microstructure-thermal property correlation of thermally sprayed coatings. Thermal transport properties of three coating systems forming composites with pores (yttria stabilized zirconia (YSZ) -Air), a second phase (Mo-Mo2C) and a graded material (YSZ-NiCrAlY) are interpreted from the point of view of microstructure and chemical composition. In the case of YSZ-Air composite, results indicate that porosity contribution from 20-35% decreases the thermal conductivity by 50-70% of the bulk value. For the intrinsic composite of Mo and Mo2C, which coexist as stable phases, thermal conductivity increases significantly with 1.75wt% carbon addition since it reduces formation of MoO2 during processing, but decreases with 3.5wt% carbon addition. This is attributed to larger carbide retention in the latter. For the discrete layered and graded composites of YSZ-NiCrAlY, which are made up of varying fractions of these two constituents, thermal conductivity decreases sharply up to 40wt% YSZ and then more gradually with increasing YSZ content. This paper examines these experimental findings by treating the these complex coatings as multiphase composites.

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