Research On Processing And Corrosion Resistance Of Double Glow Plasma Tantalizing On Pure Titanium

Commercially pure titanium has been widely used in chemical industry, metallurgy, medicine, shipbuilding and other fields, due to its high specific strength, good processability and good corrosion resistance in the oxidative, neutral, weakly reductive medium. However pure titanium suffers from localized corrosion in specific circumstances and severe general corrosion in the strong reductive medium, so these shortcomings limited its application. Tantalum (Ta) has the best resistance to corrosion in all rare metals, therefore addition of tantalum serves to improve the corrosion resistance of titanium. But because tantalum is very expensive, people are trying to find more economical ways of utilizing tantalum. Surface modification is a feasible solution to this problem. This paper proposes to form Ta modified layer on pure titanium substrate by using the double glow plasma surface alloying technique, in order to not only economically utilize tantalum but also effectively improve the corrosion resistance of titanium.To obtain good modified layers and test the properties, this paper firstly studies the processing of plasma tantalizing on pure titanium, and the microstructure, composition and phase structure of the surface modified layers are analyzed. Subsequently, the hardness, critical load values and wear resistance of the modified layers are tested, and the research focuses on the corrosion resistance and corrosion mechanism of Ta modified layers which is in the strong reductive acid and the crevice and erosion conditions.The results indicated that the process parameters of plasma tantalizing are justified as follows: source voltage: 900~950V, cathode voltage: 300~400V, processing temperature: 850~900℃, diffusing time: 3h, working pressure: 30~35Pa, distance between source cathode and work-piece: 15~20mm. The effective thickness of Ta modified layer was about 15μm, the tantalum element distribute gradually from the surface to substrate. XRD shows thatβ-Ta andα-Ti are the major phases of modified layer. The critical load values obtained by scratch testing of modified layer on pure titanium is 60N, confirming that modified layer is well adhered to the pure titanium substrates. Ta modified layer enhanced the micro-hardness and wear resistance of pure titanium substrate. The friction coefficient and wear rate of Ta modified layer on substrate decreased remarkably. Ta modified layer exhibited excellent corrosion resistance in the strong reductive acid of various concentrations. The maximum corrosion rate of Ta modified layer was less than 0.01mm. The main reasons for the high corrosion resistance was a compact, stable oxide film forming on the surface of the modified layer. Ta modified layer improved the crevice and erosion corrosion resistance of titanium. The corrosion rate of Ta modified layer was still small in the crevice and erosion conditions.