In-flight particle state has been shown to play a crucial role in determining the properties of thermally sprayed coatings. Therefore, process control strategies have been suggested to keep the in-flight particle state constant in order to decrease the variability of coating quality. Such strategies are already used to some extent in industrial applications, where the particle state is measured before starting the coating of a part to make a go/no-go decision based on whether the values are inside a predefined process window. This paper shows the importance of the evaluation procedure of the in-flight particle state, with focus on process control applications. The paper demonstrates this on the example of atmospheric plasma spraying (APS) of yttria-stabilized zirconia (YSZ), using a commercially available sensor system Accuraspray for measuring the ensemble particle temperatures and velocities as descriptors of the in-flight particle state. It is concluded that the stabilization time of the particle jet might be different from what is practically considered. Moreover, the paper investigates an approach of monitoring the in-flight particle state during a coating run without having to install the sensor system on the robot arm.

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