Coating thickness is considered to be one of the most important characteristics of thermal spray coatings. Therefore, it has long been the goal to be able to predict the coating thickness that ensues when coating an arbitrary part. A commonly applied approach is to determine the coating deposit based on a series of spray spot tests and use that for modeling the coating. Another option is to conduct spray bead tests, which better reflect the conditions during the coating. This work suggests a novel approach for in situ acquisition of the spray beads and their analysis. The acquisition is based on a 3D camera to scan the sample before and after depositing of a spray bead. The approach allows for their streamlined evaluation, enabling better understanding of spray bead formation and their modeling. The suggested analysis of spray beads includes uncertainty evaluation. This enables estimation of model prediction uncertainties which has been omitted in previous works on the topic. The analysis shows that a relative expanded uncertainty of 10% (at 95% level of confidence) can be expected for the coating thickness prediction for the simplest scenario of coating a flat sample sprayed perpendicularly at a constant spray distance and spray speed.

Coating thickness is considered to be one of the most important characteristics of thermally sprayed coatings. Despite this, there is a lack of a measurement method that could evaluate in situ the coating thickness with a sufficient accuracy that could be used as a feedback signal for online, closed-loop control. Offline methods that produce spatially resolved coating thickness measurements by capturing the surface topography have already been demonstrated to provide results with a high accuracy, comparable to the standard reference microscopical measurement method. However, up to now, the approach has not been applied in situ. This paper presents a novel approach to in situ measure spatially resolved coating thickness. It is based on a differential distance measurement of sample thickness before and after applying the coating. A high-resolution 3D camera is used to capture the surface topography and include it in the thickness measurement. The technique provides a 3D view of the deposited coating thickness measured in situ and gives results with excellent accuracy when compared to the reference microscopical method.

In this study, two different types of power supply are used in order to analyze the influence of the current output characteristics on the electric discharge characteristics. Three different plasma spray guns, namely F4, 9MB and SinplexPro, are studied with the use of different powder feedstock materials (Metco 204C-NS, Metco 71VF-NS, Metco 450NS and Hydroxyapatite C) by measuring the real-time gun voltage and current as well as the frequency spectra of the electric discharge during the spray process. In addition, a metallurgical analysis of the spray coatings is done in order to investigate the influence of the electric discharge characteristics on the spray coating quality in terms of the average coating porosity, hardness, deposition efficiency, degree of oxidation and microstructure.