Research On Corrosion And High Temperature Oxidation Resistance Of Mo And Mo-Cr Alloyed Layers On TC4 Prepared By Double Glow Plasma Surface Alloying

Titanium and its alloys, such as Ti-6Al-4V, are widely used in various fields due to their lighter quality, high ratio of strength to weight, corrosion resistance and biocompatibility. However, titanium alloys suffer from severe general corrosion in the strong reductive and oxidative medium, which prevent them from being widely applied. To solve the problems, a Mo modified layer and Mo-Cr modified layer are explored for the surface modification of TC4 alloys using double glow plasma surface alloying technique. In this paper, 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 of the modified layers which is in the strong reductive acid and sodium chloride solution and high-temperature oxidation resistance at three temperature (650℃, 750℃and 850℃).The results indicated that the process parameters 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: 15mm. The modification layer is homogeneous, continuous, and dense, the effective thickness of modified layers is about 30μm and 22μm respectively, and the elements distribute gradually from the surface to substrate. Scratch testing shows that the modified layer is well adhered to the substrates. The two modified layers enhanced the micro-hardness and wear resistance of the substrate. Immersion and electrochemical tests in the strong reductive acid and sodium chloride solutions indicate that corrosion resistance is enhanced, though with varied extent. The high-temperature oxidation resistance of three samples with different surface conditions at different temperatures showed a greater difference. At 650℃, the three samples showed excellent high-temperature oxidation resistance. At 750℃, the Mo-Cr modified layer dramatically increased the high-temperature oxidation performance of the matrix. At 850℃, the oxidation rate of the three samples increaseed rapidly, and the molybdenized Ti-6Al-4V sample completely lost its protective effect.