BOTH METALLURGY AND MATERIALS SCIENCE are concerned with the relationship between structure and the macroscopic properties of materials. Structure can be important at different levels. For example, on the atomic scale, structure dictates the strength of grain boundaries. On a larger scale, extending over many grain diameters, structure influences more complex phenomena, such as contact at surfaces or optical properties. For coatings, structure-property relationships are further complicated by the fact that coating microstructures are generally highly anisotropic and contain concentrations of defects that can vary from grain to grain for some coatings (e.g., plasma-sprayed coatings). Clearly, the ability to characterize coating microstructures is important in understanding the properties and behavior of coatings in many applications.

This article describes the structure of coatings produced by plasma spraying, vapor deposition, and electrodeposition processes. It also introduces the main techniques that can be used for microstructure assessment. Although examples are given for a limited range of deposition technologies, they are widely applicable to coatings produced by other processes.

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