Role of Ta in improving corrosion resistance of titanium alloys under highly reducing condition

Abstract

Great improvement on corrosion resistance was achieved by adding small amount of Ta into ASTM Gr13 titanium alloy. Main contribution to the improved corrosion resistance originated from the stabilized passive film in terms of the prolonged time to passivity loss. OCP results showed that the OCP transition from the passive state to corroding one prolonged with the Ta content. This behavior was also supported by EIS results, where the loop shrinkage denoting the passivity loss was retarded and/or inhibited by the Ta addition. Microstructural analysis revealed that the added Ta functioned as both substitution element and solid solution one, leading to the growth of the precipitates including β-Ti phase and formation of the complex structured passive film. Especially, the prominent stability of the passive film observed for Gr13–1.0% Ta was ascribed to the high content of the Ta oxide in the passive film, meaning that the complex oxide film required the minimum amount of the Ta oxide to obtain the excellent stability of the passive film against the high concentrated acid solution.