GRAIN BOUNDARY PRECIPITATION OF CU:NI ALLOYPLATES INDUCED BY SEA WATER CORROSION ANDIT'S INFLUENCE IN CORROSION BEHAVIOR

摘要

The cupronickel alloy (CDA715) plates were processed in order to study their seawater corrosion behavior. The specimens were mechanical polished and annealed in vacuumfurnace so as to get uniform and bright surface condition. The data of the alloy plates exposed insea area of Qingdao, Zhoushan, Xiamen and Yulin for 1, 2, 4, 8, 16 years showed specialregularity. These included the problems of unstable surface film, the film peeling off as well asthe localized corrosion occurred. The corrosion rate data taken from the specimens exposed inthe former two time intervals were much higher comparing to the data published in literaturewith the exception of those taken from Xiamen station. The observation on the corrosionmorphology and on the microstructure of the specimens by SEM and TEM respectively madethe discovery that sea water induced grain boundary precipitates. The new phenomenondepended on the microstructure of the specimens and would be in accordance with thecharacteristic of corrosion morphology. More important phenomenon was that the intergranualycorrosion occurred on near surface of the specimens and could be restrained by sea water inXiamen. The present paper discussed this mechanism by comparison it with the normalcorrosion behavior of the alloy.