Preparation and galvanic corrosion resistance of microarc oxidation ceramic coatings on ta15 alloy

The work aims to alleviate the galvanic corrosion between TA15 alloy (Ti6Al2Zr1Mo1V) and dissimilar metals caused by contact. TiO2 ceramic coating was fabricated on the surface of titanium alloy by microarc oxidation (MAO) method in silicate based electrolyte. The phase composition, microstructure and distribution of element of the coatings were characterized by characterization methods such as XRD, SEM and EDS, and the corrosion resistance was investigated by polarization curves, electrochemical impedance spectrum (EIS) and galvanic corrosion. The MAO coating was composed of inner layer and outer layer. The inner layer was dense, while the outer layer was loose and microporous. The bonding of the inner layer and matrix showed a concave and convex interface, and the phenomenon of ‘local over-growth’ appeared in some local regions. The coating mainly consisted of rutile and anatase TiO2. Compared with matrix alloy, the self-corrosion potential of the coating was increased by 0.672 V. Meanwhile, with the oxidation time increasing, the coating thickness increased and the inner layer became denser, which improved the self-corrosion potential of the coating. As the increase of oxidation time, the impedance of the inner layer increased, which was 1.16×106 Ω·cm2 (10 min), 1.2×106 Ω·cm2 (30 min), and 3.8×106 Ω·cm2 (50 min), respectively. After galvanic corrosion testing for 15 days in 3.5wt.% NaCl solution, the average galvanic corrosion rate of steel/MAO coating on TA15 alloy was significantly lower than the corrosion rate of 30CrMnSiA steel coupled with TA15 alloy, babbitt and albronze. The excellent dense barrier inner layer of the MAO coatings has good blocking features and reduces the galvanic corrosion sensitivity, thus effectively alleviating the occurrence of galvanic corrosion. © 2019, Chongqing Wujiu Periodicals Press. All rights reserved.