PLASMA NITRIDING OF AL-99.5

Aluminium nitride (AlN) is a very interesting ceramic because of its c ombination of properties such as high thermal stability, high hardness and an unusual combination of high thermal and low electrical conduct ivity. But it is very difficulty to obtain an AlN layer on the alumini um substrates by thermochemical nitriding process. Since a thin film o f aluminium oxide existing on the surface of every aluminium substrate prevents the nitrogen atoms from diffusing into the aluminium lattice . However, it is possible to sputter the oxide film away from the alum inium surface in a glow discharge with the use of plasma nitriding tec hnik and to allow the formation of AIN layer on the aluminium bulk. In the present work specimen of aluminium Al 99.5 has been plasma nitrid ed in a modified plasma nitriding unit, in which a diffusion pump was used to obtain an especially low partial pressure of oxygen in the vac uum chamber. The sputter-cleaning prior to the nitriding was conducted with the variation of the applied voltage and sputtering time. The pl asma nitriding after sputtering was carried out in a glow discharge of pure nitrogen. The metallurgical properties of the AlN-Al-composites were characterized in detail. The results show that shiny black AlN la yers with thickness up to a few micrometers have been created on the s urface of aluminum and so the enhancement of wear and corrosion resist ances of the substrate can be obtained.