Anti-Corrosion Methods and Materials

Purpose – The aim of this paper is to investigate the effect of cathodic charging and corrosion behavior of Ti-48Al-2Cr-2Nb alloy in hydrochloric acid solutions.

Design/methodology/approach – TiAl alloy specimens of thickness 0.5?mm were cathodically charged in 0.1?M HCl solution at room temperature. The prominent current densities selected for this investigation were 25 and 50?mA cm^-2 for durations of 24-120?h. The change in weight of the specimen after charging was measured by a microbalance with an accuracy of ±1?µg.

Findings – The nature of the specimen surfaces was characterized by X-ray diffraction (XRD), auger electron spectroscopy (AES) and scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). XRD revealed the phase transformation from microcrystalline to nano-crystalline, particularly after high charging times (120?h) and high current density (50?mA cm^-2). AES and EDS further assessed the compositional fluctuations on both cathodically charged and potentiodynamically polarized specimens. Surface corrosion leading to the generation of microcracks throughout the surface region was observed by SEM. Cathodic charging and the polarization process were responsible for embrittlement and pitting. Decreases in both weight and Vickers hardness values with an increase in charging time revealed that surface erosion depended strongly upon charging density.

Originality/value – The results presented in this work shed light on the role of alloying elements the passive behavior and their implications on their stability in hydrochloric acid environments.