Surface topography, corrosion and microhardness of nitrogen-diffusion-hardened titanium alloy

Mechanical-electrochemical interactions accelerate corrosion in mixed-metal modular hip prostheses. These interactions can be reduced by improving the modular component machining tolerances or by improving the resistance of t he components to scratch or fretting damage. Wrought cobalt-alloy (CoCrMo) is known to have better tribological properties compared to the titanium al loy (Ti64). Thus, improving the tribological properties of this mixed-metal interface should center around improving the tribological properties of th e Ti64 alloy. This study used scanning probe microscopy (contact, tapping a nd phase contrast mode), scanning electron microscopy, corrosion testing, a nd microhardness testing to determine the effect of a nitrogen-diffusion ha rdening process on the surface morphology, electrochemistry and surface har dness of the Ti64 alloy. The nitrogen-diffusion-hardened titanium alloy sam ples (N-Ti64) had a more pronounced grain structure, more nodular surface, and significantly (P < 0.01) higher mean roughness values than the control- Ti64 samples. The N-Ti64 samples also exhibited at least equivalent corrosi on behavior and a definite increase in surface hardness compared to the con trol Ti64 samples. The equivalent corrosion behavior and improved surface h ardness indicate the potential for N-Ti64 samples to resist similar and mix ed-metal scratch and fretting damage. The use of N-Ti64 as opposed to contr ol-Ti64 may therefore reduce the occurrence of mechanical-electrochemical d egradation in mixed-metal modular total hip prostheses. (C) 1999 Elsevier S cience Ltd. All rights reserved.