Corrosion And Corrosion-wear Behavior Of Modified Layers On Titanium And Its Alloy

Titanium and its alloys, such as Ti-6A1-4V, are widely applied to aerospace, chemical and bioengineering due to their high ratio of strength to weight, lighter quality, corrosion resistance and biocompatibility. However, their poor wear resistance is the major concerns to potential users.Numerous surface engineering technology have been explored to enhance the wear resistance of the titanium alloys while maintaining their corrosion resistance and biocompatibility. Coating, plasma immersion ion implantation (PHI), and plasma nitriding are amongst the technology explored. But cracking and debonding often occur at the modified layers at high sheer stresses. This requests we can not only consider the wear resistant oftitanium alloy but also should consider its corrosion resistance. Therefore, a Mo-N modified layer, Mo modified layer and nitrided layer were explored for the surface modification of pure titanium using an innovative plasma surface alloying technology. It has been studied that the electrochemistry property, the mechanism of Mo-N modified layer with electrochemical method and X-ray diffraction and the corrosive-wear property of Mo-N modified layer using the fretting wear with electrochemical noise measuerment. The main results have been obtained as follows:1. The component and structure of surface-modified layer have been studied. The modification layer is a duplex layer, composed of diffusing layer and surface coating. With the gradient composition distribution for diffusing layer, that results in improving the surface hardhness of titanium base.2. After the electrochemical experiment, the results indicate that open current potential of modified layer have enhanced under the same corrosion condition. Comparing with the pure titanium, its corrosion resistance has not reduced after the modified. Theelectrochemical corrosion for Mo-N modified layer in different solutions has been experimented. The results show: In each kind of medium, the anode reaction of electrode (Mo-N modified electrode) loses the electron, and then deactivates. Negative response includes two kinds reactions: an hydrogen evolution reaction in acid solution and an oxygen absorption process in neutrality or alkalinity solutions.3. Corrosion-wear behavior of untreated and plasma Mo-N modified Ti-6A1-4V alloy sliding against corundum has been studied with an electrochemical noise technique in Hanks' solution. Wear behavior of the tested alloy in ambient air of 50% relative humidity has also been studied for comparison. Results show that both wear resistance and corrosion-wear resistance of Ti-6A1-4V alloy are significantly improved by the Mo-N modification.