Voltage fluctuations are investigated for a wide range of operating conditions using the Praxair SG-100 plasma torch operated with Ar/H 2 as plasma gas. The voltage signals are characterized using statistically averaged values and power spectra. The process of anode erosion and its effect on the characteristics of the signal are described. It has been found that erosion has only little effect on the average voltage, but two characteristics of the voltage fluctuations obtained from image analysis of the voltage trace are found to be excellent indicators of anode erosion. An estimate of arc root speeds based on the voltage traces yields values of 50-100 m/s. It is estimated that the range of arc root movement and arc root speed is significantly reduced to less than one half of the original value due to anode erosion. Investigation of the effect of operating conditions and anode erosion on power spectra has been investigated and it has been observed that high frequency peaks are predominantly a characteristic of the geometry of the anode.

This paper aims to measure the residual stresses of plasma sprayed oxide ceramic deposits using the X-ray diffraction method and measure the Young’s Modulus in specially designed four-point bend test device. Aluminum oxide and chromium oxide coatings are made with a water stabilized plasma spray gun. The paper analyzes the microstructure and the phase composition. The X-ray diffraction method is used to determine residual stresses on the layer surfaces. The same method is used for the local measurement of surface tensions in a four-point bending device built into an X-ray diffractometer. This device also enables the force applied and the specimen deflection to be measured. Effective modules of elasticity are determined from the gradient from load to deflection during bending. The results of the tension measurements and the values calculated from the applied force are compared. Paper includes a German-language abstract.