This research made use of different chlorine concentrations and temperatures to explain the commercial cobalt-based super-alloys electrochemical properties and corrosion behavior of the commercial cobalt-based super-alloys in terms of the electrochemical polarization curves. Both SEM and the immersion experiments were used to explain the micro-structure and to understand the effect of temperature and concentration on the pit size. Several different solutions and concentrations were also applied to confer the critical pitting temperature (CPT) of the cobalt-based super-alloys.
In three different chloride salts, the corrosion potential (Ecorr) are of little change of temperature and concentration, and the pitting potential (Eb) gradually decreased as temperature increases. Among them, Fecl3 is a rather special case in which the difference between Ecorr and Eb in potential are relatively small which implies the alloy immediately pitted right after the specimen being scanned beyond the Ecorr.
The corrosion morphology of the alloy tested in three kinds of chloride solutions at 80oC observed by SEM shows that the corrosion all initiated preferentially at the interdendritic regions which were eventually merged into larger area as time goes on; the damage were particularly pronounced for Fecl3 than the other two.
