In this paper, two long-term experiments are conducted in order to investigate the evolution of the arc root fluctuations and the evolution of the in-flight particle state during plasma spraying. Voltage as well as the acoustic fluctuations measured at three different angles are characterized while particle state was monitored using an optical integrated system, the DPV2000. A detailed study of the evolution of the gun power, in-flight particle state (temperature, velocity, diameter, particle flux) and coating microstructure is was carried out. Results showed that the microstructure of the deposited coating significantly changed during the forty-hour spraying period. Paper includes a German-language abstract.

Presented in this paper are the results of preliminary experiments carried out for monitoring of plasma nozzle wear. The experiment system consists of two microphones, one accelerometer and voltage measurement. In the experiment, three nozzles were tested, new, used and worn. The test results show clearly the difference in acoustic characteristics with wear in the nozzle. Some observations obtained from the experiment include: 1) the microphone mounted at 45° may be the best choice for nozzle wear monitoring; 2) voltage signal could be used with the 45° microphone as an indicator for severe nozzle wear; 3) vibration signal is not as sensitive to nozzle wear as 45° microphone and voltage signal; and 4) the 90° microphone is insensitive to nozzle wear.