A Novel Approach to In Situ Coating Thickness Measurements in Thermal Spraying

Coating thickness is considered to be one of the most important characteristics of thermally sprayed coatings. Despite this, there is a lack of measurement methods that could evaluate the coating thickness in situ and with sufficiently high accuracy and precision to be useful for closed-loop process control. One of the challenges in evaluating the coating thickness of thermally sprayed coatings – both in situ as well as destructively offline, is their characteristically high surface roughness. The majority of existing coating thickness measurement methods incorporate inadequately the effect of the surface topography on the thickness measurement, producing results with low accuracy. Offline methods that produce spatially resolved coating thickness measurements by capturing the surface topography have already been demonstrated to give results comparable to the standard reference microscopical measurement method. A similar approach has also been applied already in situ to provide estimations of layer thicknesses during coating. However, up to now the approach has not been used for spatially resolved in situ measurements of coating thickness. This paper presents a novel approach to in situ measure spatially resolved coating thickness. It is based on a high-resolution 3D camera to capture the surface topography and include it in the thickness measurement.