The use of intensified plasma-assisted processing to enhance the surface properties of titanium

Intensified plasma-assisted processing (IPAP) is a surface-modification tec hnique developed recently in our laboratory. The technique can combine plas ma-diffusion treatments with chemical-reaction synthesis. Plasma intensific ation is accomplished by using a triode glow discharge at low pressure, res ulting in flux energies significantly higher than those in conventional pla sma treatments. The present work focuses on the evolution of the nitrided s urface layers in titanium. The microstructures of specimens nitrided at var ious energetic plasma conditions, ranging in magnitude between 0.5 and 3.0 mA cm(-2), have been characterized and studies conducted to investigate the growth kinetics and resulting properties. Pole-figure analysis has been pe rformed to investigate the development of preferred orientations within the nitrided layers. IPAP-treated titanium specimens exhibit high surface hard ness values and, in general, a microstructure that can consist of a TiN out ermost layer, followed by a Ti2N layer, and a nitrogen-diffusion inner zone . The development and relative amounts of the nitrides and diffusion zone a re flux-energy-dependent, with higher flux energies favoring TIN formation. Nanoindentation experiments, performed in cross-section to an indentation depth of 400 nm, demonstrate the clear effectiveness of IPAP nitriding at h igher cathode current densities in increasing hardness to significant depth s but reveal no functional dependence of modulus on treatment parameters. T ribological experiments have shown that the new plasma-nitrided surfaces po ssess significantly greater wear resistance and lower friction coefficients . (C) 1999 Elsevier Science S.A. All rights reserved.