Plasma synthesis of alumina films on metal and ceramic substrates

摘要

The authors are exploring the feasibility of the plasma synthesis of highly-adherent films of alumina and chromia on SiC and FeAl substrates. A magnetically-filtered cathodic arc plasma deposition technique is used in which a high density metal plasma (Al or Cr) is formed and deposited on the substrate in the presence of a low pressure gaseous oxygen background. The substrate is simultaneously repetitively pulse biased, providing a means of controlling the incident ion energy. In the early stages of the process the ion energy is held in the keV range so as to produce atomic mixing at the film-substrate interface (ion stitching), and in the latter stages of deposition the energy is reduced to (approximately)200 eV (IBAD range) to provide a means of controlling the film structure and morphology. Films that are dense and highly adherent can be formed in this way. The authors have produced near-stoichiometric films of alumina and chromia on small SiC and FeAl substrates and characterized the films in a number of ways, including RBS, X-ray diffraction and adhesion, and we've also done some preliminary temperature cycling experiments. The alumina films are of thickness from 0.2 to 1.5.(micro), amorphous prior to heat treatment, and show an (alpha)-alumina phase after heat treating at 1,000 C for up to 16 hours. The film substrate adhesion is typically greater then (approximately)70 MPa prior to heating, and initial results indicate that the films maintain their adhesion after repetitive cycling in temperature between ambient and 1,000 C. Here they describe the plasma processing method and outline the experimental results obtained to-date.