The mechanical integrity of WC-Co coatings is critical for their performance in wear, corrosion, and impact resistance applications. Residual stress, with its role in development of cracking, micro-cracking, and delamination, is another integral part of the mechanical characterization of the coated systems. In the given study, the residual stress of the WC-Co coatings on steel and stainless steel substrates was examined in two conditions, after deposition and after subsequent surface grinding. Several experimental techniques, including bi-layer curvature, X-ray diffraction, and neutron diffraction, were used to assess residual stress in the coatings and to enable comparison between the methods. Residual stresses induced by deposition are mostly due to rapid particle quenching and solidification upon impact, as well as any cold working induced by high velocity particle impact, but for the WC ceramic particles both effects are insignificant and result in small deposition stress. Thermal mismatch between materials of coating and substrate is the major source of stress and scale accordingly to the CTE of the substrate and coating materials and deposition temperature. It was demonstrated that the grinding applied to surface does not modify the as-sprayed residual stresses in the coatings significantly therefore assuming absence of microcracking that could have potentially affect the residual stresses.

Instrumented indentation is well-suited as a technique for probing mechanical behaviour of coatings; it requires minimal specimen preparation, can be performed multiple times on a single specimen, and can measure behaviour over various length scales, by recourse to appropriate indenter tip selection. However, the complex nature of the deformation fields under the tip, coupled with complex (e.g. anisotropy, nonlinearity) coating properties necessitates robust means of interpretation in order to extract stress-strain behaviour. Here we present a simple method, based on empirical work by Tabor, for converting coating indentation force-depth data to stress-strain curves. Using this method, results of indentation can thus be used to quantify mechanical behaviour of coatings deposited by different processes, and subjected to post-processing treatments, providing a powerful supplement to microstructural characterization. In addition, we show how anisotropic elasticity of coatings, measured via indentation, can qualitatively identify the existence of different microstructual features. Finally, we explore subsurface strain mapping as a technique to quantitatively compare elastoplastic behaviour of coatings to bulk, isotropic materials.

Splats are the building blocks of thermal sprayed coatings, and thus the mechanical properties of such coatings are directly related to splat behavior. Elastic and elastoplastic properties of coatings have been measured on the macro-scale, but are not yet quantitatively predictable using process parameters as inputs. Coating mechanical properties represent contributions from intrinsic splat properties, splat-splat interfaces, and other microscopic defects. In this study, we investigated the intrinsic properties of Ni and Ni based alloy splats on substrates, for a variety of process methods and input parameters. Residual stresses were measured via X-ray microdiffraction and elastic and elastoplastic properties were studied via nano-indentation. From a purely scientific standpoint, splat studies provide insight into rapidly cooled small-volume structures that often exhibit extra ultrafine- or nano-crystalline structure. Thus, accordingly, nano-indentation response was also compared to the prediction for bulk counterparts of the splat materials.