Corrosion behavior of Al₂O₃-WER and WC-Co-WER coatings on TC18 in neutral salt spray environment

Al₂O₃ and WC-Co water-based epoxy resin(WER) coatings for corrosion protection of TC18(with the composition of Ti-5Al-5Mo-5V-1Cr-1Fe) are prepared by air spraying. Two kinds of coating are investigated by scanning electron microscopy and x-ray diffract meter, adhesion evaluation is conducted by grid test. The results show that the coatings are continuous without defects and the level of adhesion up to 4B according to the standard of ASTM D3359. Neutral salt spray test of 750 h is carried out and corrosion resistance is measured by potentiodynamic polarization studies and electrochemical impedance analysis. The corrosion potential and corrosion current density of the WC-Co-WER coating are −0.139 V, 2.520 × 10⁻⁸ Acm⁻², respectively, and Al₂O₃-WER coating are −0.195 V, 2.891 × 10⁻⁸ Acm⁻², respectively. The protective efficiency of the WC-Co-WER coating is 87.6%, which is higher than that of the Al₂O₃-WER coating with 85.8%. Epoxy resin has good corrosion resistance, the surface of WC-Co-WER coating has more epoxy resin due to sedimentation of the WC-Co particles, WC-Co particles concentrate inside the coating retard infiltration of the corrosive. The above characteristics made the WC-Co-WER coating perform better in corrosion resistance. (paper)