It is generally known that plasma sprayed coatings exhibit rather a low strength thanks to their characteristic microstructure with porosity and microcracks. To determine the role of varying types of deformation in different parts of the coatings profile, 1.8 mm thick chromia coatings on a steel substrate were made using WSP plasma spray. Stress gradients were then measured "in-situ" on a four-point bending device during bend deformation of the coated beam using neutron diffraction. Only compressive loading in coatings increased the resulting stresses. From the plot of stresses vs. applied strain (linear dependence) the Young’s moduli of the substrate and the coating were determined. Both values agree well with those obtained by mechanical testing. In general it is believed that, in a simplified way, interlamellar voids (cohesion defects) roughly parallel to the substrate decrease the tensile strength in the direction perpendicular to the substrate, while intralamellar cracks, roughly perpendicular to the substrate, significantly affect the Young’s modulus of coating. It is supposed that the tensile deformation of coatings opens the cracks and no stress increase is observed. On the other hand the applied compressive deformation in the coating closes the intralamellar microcracks and the internal stresses increase, as suggested by obtained results.

Properties of thermally sprayed coatings, including residual stress, are controlled by various parameters of the spraying process. This study is focused on three thermal spraying techniques with significantly different particle temperatures and velocities. These are plasma spraying, twin wire arc spraying and high velocity oxy-fuel spraying. For each method, in-flight particle diagnostics was performed. Through-thickness residual stress profiles in Ni+5%A1 coatings on steel substrates were determined nondestructively by neutron diffraction. The stresses range from high tensile in the plasma sprayed coating to compressive in the HVOF one. Various stress generation mechanisms, including splat quenching, peening, and thermal mismatch, are discussed with respect to process parameters and material properties.