REDUCTION OF FRETTING CORROSION OF TI-6AL-4V BY VARIOUS SURFACE TREATMENTS

Titanium and titanium-6% aluminum-4% vanadium (Ti-6Al-4V) are known to -be biocompatible and corrosion resistant. However, there have been nu merous reports of elevated tissue levels of titanium due to passive di ssolution, wear, or fretting corrosion of implants. Studies were under taken to determine whether the fretting corrosion of Ti-6Al-4V could b e reduced by surface treatment of one or both surfaces in a fretting s ituation. Three different surface treatments were studied: ion implant ation, physical vapor deposition nitriding, and plasma ion nitriding. The specimens used were screws fretting against the countersinks of a two-hole plate. Fretting corrosion was assessed by weight loss, by che mical analysis of test solutions, and by scanning electron microscopy. Surface treatment of one component, the screws, resulted in reduction in the release of titanium to only 18-32% of that seen with the untre ated controls. Weight loss of the untreated plates fretted against phy sical vapor deposition nitrided screws and plasma ion nitrided screws was reduced to 31 and 38% of the control, respectively. The weight los s of plasma nitrided screws was only 30% that of the control. Nitridin g of both plates and screws resulted in a further decrease in plate we ight loss and metal release. Plasma ion nitriding of both components h ad the most significant effect, with the weight loss and titanium rele ase being only 11 and 2% of the control values, respectively.