Abstract: Under silicate system and dual pulse constant pressure mode, the bi-electrodes micro-arc oxidation and traditional micro-arc oxidation techniques were used to grow ceramic coating in situ on the surface of tantalum metal. The thickness of the coating was tested by using thickness gauge. The phase composition, surface morphology and element content of the coating were analyzed by using X-ray diffractometor, scanning electron microscope and energy dispersive spectrometer. The high-temperature oxidation resistance of the coating was studied by using high-temperature oxidation mass gain test. The results indicate that the phase composition of the coating formed by traditional micro-arc oxidation and bi-electrodes micro-arc oxidation reactions is Ta₂O₅ phase. The coating thickness generated under traditional micro-arc oxidation mode is greater than that under bi-electrodes micro-arc oxidation mode. After high-temperature oxidation, the surface of the coating is smoother compared to that before oxidation, indicating that the oxides melt and collapse after oxidation, and there are obvious sintering traces, with some remained volcanic crater-like small pores. High temperature oxidation causes the oxide to extrude and expand, resulting in microcracks. Compared with the matrix, the specimens subjected to micro-arc oxidation have better resistance to high-temperature oxidation. The ceramic coating generated in situ by bi-electrodes micro-arc oxidation technology has less high-temperature oxidation mass gain and better resistance to high-temperature oxidation compared to that of traditional micro-arc oxidation technology.

Key words: tantalum, bi-electrodes micro-arc oxidation, high-temperature oxidation resistance, ceramic coating