کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1471983 | 990367 | 2007 | 16 صفحه PDF | دانلود رایگان |
To quantify the extent of chromium depletion, electrochemical potentiokinetic reactivation tests were performed on solution-annealed (1393 K) and solution-annealed followed by ageing at 973 K for 4 h or 16 h samples of austenitic Alloy 690. The electrochemical studies indicated very high equilibrium chromium concentration at the chromium carbide/matrix interface for the aged samples. A new electrochemical test parameter that is the ratio of peak activation to maximum passive current density (defined by Ia/If) was considered to express the extent of chromium depletion. The alloy, in three different heat-treated conditions, revealed unstable passivity in deaerated 5% and 10% NaOH solutions at 295 K. A comparatively higher passive current density of the aged samples in deaerated caustic environments than the annealed one could be attributed to reactivity of Cr-carbides with the caustic. Microscopic studies indicated that the TiN inclusion/matrix interface may provide a preferred site for pit initiation in caustic environments, which could be attributed to large degree of misfit between TiN inclusion and austenite matrix.
Journal: Corrosion Science - Volume 49, Issue 2, February 2007, Pages 303–318