Abscheidung und Charakterisierung von PECVD-Aluminiumoxidschichten

Nowadays, thin films are used widely to increase the life-time of the tooling surfaces. Alumina coatings are known to exhibit advantageous mechanical properties as well as chemical inertness and oxidation resistance at high temperatures. Hence, this material is a suitable candidate for coatings used in wear- and high temperature protection-applications. Various deposition techniques including chemical vapour deposition (CVD) and physical vapour deposition (PVD) were applied to produce alumina thin films. Alpha-alumina films can be obtained by CVD only at temperatures above 1000ºC. This rather high deposition temperature limits the suitable substrate materials for tooling applications essentially to cemented carbide. In the PECVD deposition process the ionised and excited gaseous particles are striking the film surface during the growing. By the collisions with ions adsorbed particles receive additional energy which leads to a high mobility and therefore to the change of the film structure.This plasma activation of the deposition process makes possible to deposit films at lower substrate temperature than with conventional thermal CVD. In this work a significant step towards the synthesis of a-alumina at lower substrate temperatures is reported: the formation of Alpha-alumina thin films at 580ºC substrate temperatures. The results are present in the form of a diagram correlating the phase formed with the substrate temperature and the cathode power density. Finally, the ion energy which are strike the growing films is discussed with respect to phase obtained. The effect of the power density at the cathode and the substrate temperature on the film mechanical properties and constitution was investigated by nanoindentation and X-ray diffraction, respectively. The performance of alumina coatings for the semi-solid processing of steel was studied with respect to tribological properties, adhesion and resistance to thermal shock. Based on the here presented adhesion and thermal shock data it can be concluded that the alumina thin films are suitable candidates for the die protection during semi-solid processing of steel