DC MAGNETRON SPUTTERING OF OXIDATION-RESISTANT CHROMIUM AND CRN FILMS MONITORED BY OPTICAL-EMISSION SPECTROMETRY

For applications at temperatures above 500-degrees-C, Ti-6wt.%Al-4wt.%V was protected by sputtering chromium and chromium nitride layers from the embrittlement caused by oxidation. The coating processes were analysed in situ by means of optical emission spectrometry, whereby the deposition rate and the stability of the actual process conditions were monitored. Further, the nitridation of the chromium target (the source of the coating material) and the concentration ratio of the condensing binary compounds (Cr(x)N(y)) can be assessed during the process. Compared with the uncoated material, the mass gain of Ti-6wt.%Al-4wt.% V due to oxidation could be decreased to about 3% by means of chromium and chromium nitride layers 3-mu-m thick. Also the brittle alpha case formation at the near-surface region of the titanium alloy is greatly reduced in the course of high temperature oxidation. As far as diffusion and reaction are concerned, an interpretation of the oxidation process on the titanium alloy is given by means of Auger depth profiles. The morphology of the layers is characterized by scanning electron microscopy pictures.