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Processing-Microstructure-Property Relations in AnisotropicThermal Sprayed Composites

Published online by Cambridge University Press:  26 February 2011

Weiguang Chi
Affiliation:
wchi@ic.sunysb.edu, State University of New York at Stony Brook, Materials Science and Engineering, Heavy Engineering 130, Stony Brook, NY, 11794, United States, 631-216-2538
Vasudevan Srinivasan
Affiliation:
vsriniva@ic.sunysb.edu, Stony Brook University, Materials Science and Engineering, Stony Brook, NY, 11794, United States
Atin Sharma
Affiliation:
atsharma@ic.sunysb.edu, Stony Brook University, Materials Science and Engineering, Stony Brook, NY, 11794, United States
Sanjay Sampath
Affiliation:
ssampath@ms.cc.sunysb.edu, Stony Brook University, Materials Science and Engineering, Stony Brook, NY, 11794, United States
Richard Gambino
Affiliation:
rgambino@ms.cc.sunysb.edu, Stony Brook University, Materials Science and Engineering, Stony Brook, NY, 11794, United States
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Abstract

Thermal spray is a significantly advanced but inherently complex depositionprocess that involves successive impingement of molten droplets on asubstrate to form coating with a ¡°brick-wall¡± layered structure. Theanisotropic microstructure of coatings is very sensitive to processingconditions and has significant influence on the properties. This study aimsto understand the processing-microstructure-thermal property correlation ofthermally sprayed coatings. Thermal transport properties of three coatingsystems forming composites with pores (yttria stabilized zirconia (YSZ)-Air), a second phase (Mo-Mo2C) and a graded material (YSZ-NiCrAlY) areinterpreted from the point of view of microstructure and chemicalcomposition. In the case of YSZ-Air composite, results indicate thatporosity contribution from 20-35% decreases the thermal conductivity by50-70% of the bulk value. For the intrinsic composite of Mo and Mo2C, whichcoexist as stable phases, thermal conductivity increases significantly with1.75wt% carbon addition since it reduces formation of MoO2 duringprocessing, but decreases with 3.5wt% carbon addition. This is attributed tolarger carbide retention in the latter. For the discrete layered and gradedcomposites of YSZ-NiCrAlY, which are made up of varying fractions of thesetwo constituents, thermal conductivity decreases sharply up to 40wt% YSZ andthen more gradually with increasing YSZ content. This paper examines theseexperimental findings by treating the these complex coatings as multiphasecomposites.

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