Two new inner contours of de Laval nozzles (V70, V21) for F4 torch, which have already successfully been established for the Atmospheric Plasma Spraying (APS) are investigated for application under Vacuum Plasma Spraying conditions (VPS). Studies have been performed with regard to power efficiency, sound level and arc voltage fluctuations as well as coating quality and deposition efficiency for use of CoNiCrAlY powder as feedstock material. The results are compared to the commonly used standard VPS nozzle. CFD calculations and enthalpy probe measurements of plasma gas velocity and temperature distribution in the centreline of the supersonic plasma jets are carried out in order to get insight in the basic dependencies.

An optimised de-Laval-type-contour for the Atmospheric Plasma Spraying (APS) with respect to the thermal and deposition efficiency as well as to the arc voltage fluctuations and the sound level of the plasma torch is presented. Investigations of the plasma gas dynamics and two different feedstock materials (Al 2 O 3 (fused and crashed) and Cr 2 O 3 (agglomerated and sintered)) have been done to promote the industrial utilization of convergent-divergent nozzles for the APS.

A modified Laval-like-contour for a convergent-divergent nozzle is presented for the Atmospheric Plasma Spraying (APS). The influence of the nozzle design on the thermal and deposition efficiency as well as on the arc voltage fluctuations and the sound level of the plasma torch are investigated and compared with former investigations. The improvements of the quality of DC-Plasma sprayed Al 2 O 3 coatings by the nozzle design is shown by the coating porosity, adhesive and breakdown strength. A 2D-model presents the gas dynamics inside the nozzle. The intention of this study is to promote the industrial application of convergent-divergent nozzles for the APS in conjunction with the optimisation of the plasma gas dynamics.

This paper investigates the influence of nozzle design on the quality of Al 2 O 3 coatings produced by atmospheric plasma spraying. It compares the thermal and deposition efficiency of different plasma guns along with the porosity and adhesion strength of the resulting coatings. The intent of the study is the application of convergent-divergent nozzles as an economic alternative to the nozzles typically used for atmospheric plasma spraying. Paper text in German.

In the present work ceramic particles (Al 2 O 3 , YSZ) are sprayed onto steel substrates using a radio frequency inductively coupled atmospheric plasma spray process (IC APS). Because of the low plasma velocity and the large plasma volume large particles can be completely melted. The particles reach the substrate with low velocities (in the order of 10 m/s). So, a special kind of deformation can be observed. Some characteristic values of impact and deformation are also quite different from some other thermal spraying technologies. Of course, that has an strong influence on the coating properties. It is shown, that a high kinetic energy of impinging particles is not an essential assumption for a high bond strength and a low porosity of the coatings. IC Plasma sprayed particle splats are investigated and compared with DC and HVOF sprayed ones. The influence of the particle impact and deformation on the coating properties is demonstrated. It is shown, that in spite of the low particle velocities coatings can be sprayed by IC APS with comparable quality, but with quite different coating properties such as the crystalline structure.

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.