ON THE MECHANISM OF INTENSIFIED PLASMA-ASSISTED PROCESSING

Intensified plasma-assisted processing (IPAP), is a surface modificati on technique developed recently in our laboratory. Plasma intensificat ion is accomplished by triode discharge and can be utilized for low-pr essure, low-temperature diffusion treatments and synthesis of a range of advanced compounds. The energetic flux of ions and neutrals generat ed in IPAP can create highly favorable surface conditions producing si gnificant improvements in properties ranging from thermal and chemical stability to wear resistance. The objective of the present study was to investigate further the role of energetic particle bombardment on t he modification process. IPAP nitriding experiments were carried out o n Ti-6Al-4V substrates at specific nitrogen flux levels and Bur energi es. Parallel experiments were performed by low-energy, broad-beam nitr ogen implantation at comparable ion energies and dose levels. Nitrogen concentrations and penetration depths were determined by depth profil ing using AES and microhardness measurements. The experimental results were used to derive effective nitrogen diffusivities to assess the ef fect of the energetic particle bombardment on the diffusion process. F or both IPAP and ion implantation, nitrogen diffusion into titanium ni tride and solid solution layers is greatly accelerated compared to con ventional ion nitriding. IPAP is almost as effective as low-energy ion implantation in enhancing nitrogen penetration when the two processes use ions of similar energies and dose levels. The energetic neutrals present in IPAP appear to further enhance the growth of surface nitrid e layers. Analysis also indicates that an optimal ion energy may exist . (C) 1997 Elsevier Science S.A.