Quantifying Thermal Spray Coating Architecture by Stereological Protocols: Part I. A Historical Perspective
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JTTEE5 16:6–14 DOI: 10.1007/s11666-007-9017-8 1059-9630/$19.00 ASM International
Quantifying Thermal Spray Coating Architecture by Stereological Protocols: Part I. A Historical Perspective Ghislain Montavon and Guy Antou (Submitted January 8, 2007) This article presents, from a historical perspective, some stereological protocols of the first order. Such protocols can be implemented to quantify statistically the architecture of thermal spray coatings and their relevant features (pores, lamellas, etc.). A forthcoming Part II of this article will address some key points to implement, from a practical point of view, such protocols.
Keywords
stereology, history, image analysis, structural quantification
1. Quantification of Thermal Spray Coating Architectures Thermal spray coating structures are built up by stochastic stacking of lamellas resulting from impact, flattening, and rapid solidification of impinging molten or semimolten particles. These structures form a complex three-dimensional (3-D) structure with combination of unique features, such as flattened lamellas, globular pores, intralamellar cracks, interlamellar delaminations, unmolten near-spherical particles, and their related core-shaped pores, among the principal ones. The coating in-service properties derive to a large extent from the coating architecture that itself depends on the spray parameters (power, feedstock injection, environmental, kinematics, etc.) and the feedstock characteristics (nature, particle size distribution, impurities, etc.). Quantifying coating structural attributes is hence of prime importance for optimizing spray parameter set to obtain desired in-service properties or, on a more daily basis, for controlling coating quality. Numerous experimental techniques are available to study thermal spray coating structures from the points of view of their composition, phase content, architecture, and so forth. These techniques can yield qualitative or quantitative results, depending on selected protocols. Metallography is a commonly implemented technique, as it allows one in a relatively ‘‘simple’’ and ‘‘quick’’ way G. Montavon, SPCTS–UMR CNRS 6638, Faculty of Sciences, University of Limoges, 123 Avenue Albert Thomas, 87060, Limoges Cedex, France; and G. Antou, SPCTS–UMR CNRS 6638, Ecole Nationale Supe´rieure de Ce´ramiques Industrielles, 47–73 Avenue Albert Thomas, 87065, Limoges Cedex, France. Contact e-mail: [email protected]
6—Volume 16(1) March 2007
to address the coating architecture or to scan the coating/ substrate interface to assess the absence of visible delamination, embedded grit media, and so forth. Several specific and very strict arrangements have to be utilized to prepare samples. This involves implementing optimized and reproducible metallographic protocols—from sample cutting to sample polishing—to limit to the maximum possible extent the introduction of artifacts such as cracks, scratches, pull-outs, and so forth. While the metallography is widely encountered within the thermal spray community, the coati
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