This paper investigates the problem of complete evaporation of zirconium oxide powders that are injected into a thermal RF plasma. Particle trajectories and evaporation are studied using optical emission spectroscopy and laser Doppler anemometry. Model calculations are compared with the results of process diagnostics. It is observed that axial emission profiles confirm the influence of the particle size on the evaporation behavior. Paper includes a German-language abstract.

DC plasma spraying with its products has gained a high technical importance. With the availability of technically reliable high-frequency plasma torches whose basic development can be traced back to about 40 years ago, some of the disadvantages of the DC spray method are no longer existing or can be avoided to a great extent. This paper describes the principle, construction, and function of high-frequency plasma torches in which the plasma is generated by induction and metallic electrodes are not required (as is the case with conventional DC plasma torches). Typical examples of HF plasma spray application are discussed. Paper includes a German-language abstract.

DC plasma spraying has been widely recognized as a quick and economic way to produce all kinds of coatings (metals, alloys, and ceramics) for a variety of applications. There has been a growing interest in using radio frequency (RF) plasmas. Studies have been reported on characterization of plasma-sprayed coatings by TEM, including thermal barrier coatings, alumina coatings, and Ni-Al coatings. There are, however, no detailed studies reported on microstructural comparisons of coatings prepared by RF and DC plasma spraying. In this paper, XRD, SEM, TEM, polarizing OM, four-point bending fracture, and molten particle impact behavior are used to clarify microstructural differences between the RF- and DC-coatings. The results showed that the microstructures were much different for both cases, especially in the interfacial region between the coatings and the substrates. Paper includes a German-language abstract.

This paper compares the features of direct current and radio frequency (RF) plasma spraying, but also the properties of aluminum coatings that are reinforced with short carbon fibers and manufactured using these two methods. It shows that the embedding of the fibres during the RF plasma spray process is very poor due to the low velocity of the plasma jet. Paper includes a German-language abstract.