Preparation of Micro Arc Oxidation Ceramic Coatings and the Research of Interfacial Bonding Strength
|School||Harbin Institute of Technology|
|Course||Chemical Engineering and Technology|
|Keywords||Ti-6Al-4V alloy Micro-arc oxidation Ceramic films Thermal-impact resistance Interface bonding|
In the paper, the ceramic coatings were prepared in situ on Ti-6Al-4V alloy by micro-arc oxidation （MAO）.The phase composition, microstructure and thermal-impact resistance of the ceramic coatings were studied in different Na2SiO3 concentration electrolyte and electric parameter. The conditions for the preparation of the ceramic coating were optimized. The characteristics and the primary influencing factor of the interface bond layer between ceramic coatings metal and TC4 substrate were discussed.The phase composition, morphology of the coatings was studied by X-ray diffraction （XRD）, and the scanning electron microscopy（SEM）. The elements and the distribution characters were examined by energy dispersive spectrum （EDS） and X-ray photoelectron spectroscopy （XPS）. Thermal-impact resistance of the ceramic coatings and interface bonding intensity were studied by the thermal impact test and tensile test.The results showed that the phase composition, coating structure were affected by the electrolyte concentration and electric parameter. The ceramic films were composed mainly of rutile and anatase TiO2 and amorphous silicon oxide. The Ti element exist in the form of Ti4+ in the coatings. In the condition of pulsed double-polar micro-arc oxidation, with the increasing of Na2SiO3 concentration, oxidation time, cathode current density and electrical source frequency, the thickness of ceramic films increased. As positive current density increasing, the content of rutile and anatase TiO2 was improved. The content of rutile TiO2 firstly increased and later decreased with the negative current density increasing. The content of Si in the surface of coating was improved with the increasing of Na2SiO3 concentration, electrical source frequency and oxidation time. The content of Ti changed on the contrary. In the single-polar pulse power, the thickness of coatings was thinner than in double-polar pulse power and as anode pulse density increasing, the content of rutile TiO2 improved. The changing regular of the content of Si and Ti in the surface coating was consisitent with that in double-polar pulse power.In the double-polar pulse power condition, the thermal-impact resistance of the coatings was evidently better than that in the single-polar pulse power condition. And the thermal-impact resistance of the coatings was closely related to the Na2SiO3 concentration, cathode current density, oxidation time and electrical source frequency. The results of thermal-impact resistance and the character of coating structure showed that the coatings prepared at 40g/L Na2SiO3 concentration , Ia/Ic=9/9, oxidation time 30min, frequency 3000Hz, had the best thermal-impact resistance.The ceramic coating and substrate engaged each other in the interface, and integregated closely. The bonding intensity of interface between coating and substrate, was related closely to the preparing conditions. The value of bonding intensity of ceramic coatings prepared in the double-polar pulse power was lower than in the single-polar pulse, the suitable cathode current help to improve the bonding intensity of interface, but further increasing cathode current will reduce the bonding intensity of interface, the bonding intensity of interface between coatings and sunstrate was the largest at the optimal conditions, which was up to 26.84MPa.