Influence of micro-structure on corrosion behavior of a Ni-based superalloy in 3.5% NaCl

The electrochemical corrosion behavior of a Ni-based superalloy with polycrystalline (cast alloy), single-crystalline (SC (2 0 0)) and nanocrystalline (NC) micro-structures has been studied in 3.5% NaCl solution. The results indicated that among the three materials, the corrosion resistance increased in the order cast alloy < SC (2 0 0) alloy < NC coating. XPS analyses revealed that the composition of passive film on the three materials was different. In addition to Cr2O3 and TiO2, some NiO was detected in the passive film on the cast alloy, little in that of the SC (2 0 0) alloy and none in that of the NC coating. The double-log plots showed the compact property of the passive film formed on the samples also varied in the order cast alloy < SC (2 0 0) alloy < NC coating, with the cast alloy displaying the worst compact property and the NC coating the best. The micro-structure influenced both the composition of passive film as well as the initial growth of passive film, which determined the compact property of the film and resulted in the observed differences in the corrosion behavior of the three materials. (C) 2007 Elsevier Ltd. All rights reserved.