A novel integrated temperature investigation approach of sprayed coatings during APS process

Coating temperature is important for the coating reliability and reproducibility during the process of atmospheric plasma spray. A novel measurement and control approach for substrate and coating temperatures is presented. It is based on infrared (IR) pyrometry combined to specific robot spray trajectories in order to avoid harsh environment of spray workshops. The temperature evolution is continuously detected and recorded during preheating, spraying and cooling stages. The two specific factors, periodic average temperature and standard deviation were adopted to evaluate the temperature variation and the fluctuation of the thermal cycle relevant to one robot spray cycle based on the statistical method. These two factors are successful in describing the temperature variation during experimental processing sets. Finally, based on the monitoring system, the influence of Z-type robot spray trajectory parameters, including spray distance, scanning velocity and scanning step on coating temperature characterized by the two factors, is systemically investigated. Experimental results show that average temperature has no evident difference as a function of scanning velocity and no fixed relationship with scanning step, but just is dominated by the heating time of plasma jet and particle flux. Therefore, the selection of optimal scanning velocity just needs to take the temperature fluctuation into consideration. The temperature fluctuation decreases when scanning step increases, but both average temperature and fluctuation decrease with the increasing of spray distance and vice versa. Finally, on the basis of experimental results, a control experiment of sprayed coating temperature is presented to obtain constant temperature cycles by means of adjusting robot trajectories, cooling, among other considered operating parameters. Excellent control performance is observed.