Ei. Meletis et al., The use of intensified plasma-assisted processing to enhance the surface properties of titanium, SURF COAT, 113(3), 1999, pp. 201-209
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.