Study Of Property And Organization Of Cu-Cr-Alloyed Layer On Titanium Alloy Surface

As a new metal material, because of its superior high specific strength, specific stiffness, anti-corrosion, mechanical property at high temperature, anti-fatigue, titanium alloy has been widely applied in aerospace,ship-building and sport equipment industry. And it has also been extensively used in some special fields, such as medical health and food processing.With the improvement of people’s standard of living, titanium alloy has been requested to be equipped with antibacterial property.In order to achieve this goal, alloying Ti-alloy was prepared through double glow plasma chromizing process with Ti-6Al-4V as substrate and Cu, Cr as pre-seeding metal in this experiment. The antibacterial properties was tested and the wearing resistance was also detected. The X-Ray Diffraction(XRD), scanning electron microscope(SEM) and Energy Dispersive Spectrometry(EDS) were used in order to observe and analyze the phase structure and elementary composition of the coatings, and Optical microscopy with3D function was used to detect the wear depth. The corrosion resistance of substrate and the alloying layers was examined by adoption of immersion method in0.5mol/L NaCl solution,0.5mol/L citric acid solution and0.5mol/L NaHCO3solution. The conclusions are as follows:(1) The CuCr alloyed layers formed on the surface of Ti-6Al-4V exist as granulates. There is an obvious boundary between coating and substrate. The coatings are composed of Ti, Cr2Ti, CuTi2and other solid solutions. The copper concentration is about12.3wt%and the chromium concentration is about14.1wt%, the thickness of the alloyed layer is about12μm when the target has a ratio of Cu content to Cr content5:5used; While, for the target with a ratio of Cu content to Cr content7:3, the copper concentration in the alloyed layer is about16.6wt%, and the chromium concentration is about5.9wt%, the thickness is about40μm; a little of acicular structure was detected in the alloyed layer, around which some significant cracks were observed.(2) The CuCr alloyed layers which were formed on the surface of Ti-6Al-4V showed excellent antibacterial property against Gram-negative E.coli and Gram-positive S.aureus. The antibacterial rate was100%. Here are three main mechanisms for the high antibacterial rate:A. Antibacterial role by electrostatic adsorption; B. Antibacterial role by metal ions diffusing across cell walls and destroying the synthetase; C. Antibacterial role by catalysis.(3) The friction and microhardness were tested on the layers. The microhardness of alloyed layer is3020.84gf/mm2and the wear depth is7.81μm when the target has a ratio of Cu content to Cr content5:5. The microhardness of alloyed layer is3043.32gf/mm2and the wear depth is21.15μm when the layer was prepared by a target with a ratio of Cu content to Cr content7:3. The microhardness of substrate is2181.44gf/mm2and the wear depth of it is22.47μm. The test shows that wear resistance of layer was the best when prepared by the target with a ratio of Cu content to Cr content5:5.(4) The anti-corrosion behavior of the CuCr alloyed layers formed on the surface of Ti-6Al-4V was detected in NaCl solution and citric acid solution. It turns out that the anti-corrosion property becomes lower after the alloying treatment, but not obviouly. The layer prepared by the target with a ratio of Cu content to Cr content5:5is better than the layer produced by another target with different ratio. When NaHCO3is used to conduct the test, the anti-corrosion property of alloyed-layers was much better than that of the substrate, and the layer prepared by the target with a ratio of Cu content to Cr content5:5is better than the coating produced by another target with different ratio.(5) A little α’ martensite was detected in the alloyed layer which was prepared by the target with a ratio of Cu content to Cr content7:3. And around the structure there existed some significant cracks. It resulted in the shedding of that layer during the friction and wear test and thus the decreased surface properties. Because the coating prepared by the target with a the ratio of Cu content to Cr content5:5is much better not only in properties but also in organization structure, it is more suitable for application in medical health and food processing.