**4.2.2 Experimental**

186 Ceramic Coatings – Applications in Engineering

This finding is another example for the low comparability between tribometer experiment and hot extrusion, as the billet is pressed under air exclusion in the container. Another guess is a lack in thermal stability of the Andersson phases. Other SPS coatings sprayed with the same feedstock composition where tempered at different temperatures (300, 500 and 800° C) for several hours. The colouring of the coatings changed with temperature (see top views on the left hand side of **Figure 13**), as the phase composition changes (see the corresponding diffraction patterns on the right). The marked peaks in the diffraction pattern of the sample tempered at 500° C are caused by the Andersson phases. As clearly can be seen, this peaks are significantly smaller in the sample being not tempered and that one tempered at 800° C. So it can be stated, that the tribological active phases can be formed with rising temperature within the coatings during operation, but also may decompose with further increased

Fig. 13. Alteration of the phase composition of Andersson type coatings in relation to temperature (right side) and corresponding top views of the tempered samples

experiments using aluminium and copper based extrusion alloys.

By means of x-ray diffraction analysis it could be proven, that the mixing of titania and other oxide feedstock in the SPS process could be realized. For example the achieved Andersson type coating system sprayed with titania and chromia containing suspensions showed a temperature induced lowering of their coefficient of friction when rotated against 100Cr6. Further experiments will be conducted to better understand the parameters controlling the mixing process of the feedstock on one hand and regarding tribological

**4.2 Comparison of multielectrode plasma guns for development of new coatings** 

When high throughput is intended, three cathode guns are a supposable solution. Due to their stationary plasma jet and elevated power characteristics, higher feeding rates concurrent with sufficient deposition efficiencies can be realized compared to one-cathode plasma guns. On the contrary to those well-known equipments a newly marketable system

temperatures.

**4.1.3 Conclusion** 

The workings concentrated on the investigations, to what extent both gun concepts are appropriate for inert and reactive shrouded plasma spraying as well as the processing of nanoscaled suspensions. Feedstock was used being not commonly applied in plasma spraying to identify the potential of plasma spraying for possibly new applications. For demonstration purposes coating systems of titanium and chromium as well as their nitrides and Indium-Tin-Oxide (ITO) showing electrical conductance were chosen. For the chromium coatings feedstock obtained from GTV GmbH with two different particle size distributions (-25+5 µm and -45+5 µm) were investigated. As titanium feedstock a powder of -45+10 µm came into operation, which is manufactured and distributed by TLS Technik Spezialpulver GmbH (Bitterfeld/Germany). For SPS suspensions containing 5 wt.-% ITO (ANM PH 15695, Evonik Degussa GmbH, Marl/Germany) and Al2O3 (Saint Gobain, Weilerswist/Germany) with primary crystallite sizes of some tens for the first and approximately 150 nm for the latter were used.
