It has been reported by the authors that Al2O3/Al/Al2O3/Al multilayer and Al2O3·Nb composite films have self-healing ability. The aim of this study is to make clear the most preferable composition of the Al2O3·Nb composite film for self-healing and presume the self-healing mechanism of the films. Al2O3·Nb composite films with various composition were prepared on an Fe thin film formed on a glass substrate by ion-beam-sputter deposition. The self-healing ability was evaluated by the repassivation behavior of potential and current on specimens just after giving a knife-scratch in 1.0 kmol·m-3 Na2SO4 and NaCl solutions. The chemical state of constituent elements of the composite films was analyzed by XPS and the micro- and crystal structures of the films were examined by TEM. The surface of the specimens after scratching was analyzed by AES combined with Ar+ ion sputtering. The activation and repassivation behavior of potential and current on the specimens after scratching showed the specimens, except for those with high Nb content, have the self-healing ability in a Na2SO4 solution. However, the specimen that has a mole composition ratio of Al2O3: Nb = 92: 8 only showed the self-healing ability in a NaCl solution. The XPS analysis showed that the oxidation state of Nb in the composite films changed with composition. The AES analysis revealed that the composite films were not removed completely by scratching. Most of composite films with plastic deformation adhered on the Fe film after scratching. These results show that the defects generated by scratching should be microscopicically small. The self-healing should results from filling up the defects with oxides generated by the oxidation of Nb metal and/or lower valance Nb oxides in the films.
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