Fundamental and applied aspects of the plasma-assisted nitriding process for aluminium and its alloys

The insufficient wear resistance of aluminium and its alloys is a well-known problem. Different surface treatment methods have been developed to increase the resistance. Compared to the electrochemical processes, the plasma-assisted nitriding of aluminium is a new method without ecological problems. In this paper different possibilities of plasma-activated nitriding are introduced. Due to the low electrical conductivity of the aluminium nitride coating formed, an rf plasma process has some advantages compared to a dc discharge. Furthermore, comparisons are made with high-energy ion implantation and a low-energy ion-assisted deposition. The morphology and composition of the resulting aluminium nitride layers are shown. A sputtering process prior to nitriding is of great importance. The influence of the gas phase composition and the plasma parameters were examined by plasma mass spectrometry. The ion energy distribution of the detected species indicates different possible charge transfer processes which art influenced by the gas phase composition. (C) 1997 Elsevier Science S.A.