Processing-Microstructure-Property Relations in Anisotropic Thermal Sprayed Composites
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Processing-Microstructure-Property Relations in Anisotropic Thermal Sprayed Composites Weiguang Chi, Vasudevan Srinivasan, Atin Sharma, Sanjay Sampath, and Richard Gambino Materials Science and Engineering, Stony Brook University, Stony Brook, NY, 11794
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 “brickwall” 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.
INTRODUCTION Thermal spray technique was introduced by Dr. Schoop in the early 1900s [1] and used to produce protective coatings to fulfill a variety of functions such as corrosion resistance, wear resistance and thermal barriers in aerospace, automobile, marine, pulp, and petrochemical industries. With its wide use, the thermal spray technique has become an integral materials processing tool for fabricating coatings with expected microstructure and properties by varying process parameters. The increased need for design-based implementation extends the application of thermal spray technique to produce composite coatings to enable tailoring the coating thermal, physical and mechanical properties. The thermal spray technique offers versatility and flexibility essential for the design and development of such composite coatings. However, the inherent complexity of thermal spray process and coating microstructures represents a great challenge of establishing process-microstructure-property relations. A fundamental understanding of the microstructure-properties (in this case thermal conductivity) is essential for process optimization and microstructural control. In this study, a systematic assessment for composite coatings of YSZ wi
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