Intergranular oxidation of Ni-based Alloy 600 in a simulated PWR primary water environment

Abstract

Oxidation testing of Alloy 600 was conducted in PWR simulated primary water to obtain a clear understanding of intergranular cracking. The degree of intergranular oxidation was highly dependent on the grain boundary character. Random high-angle grain boundaries were deeply oxidized, and nano crystalline Cr2O3 oxides formed. However, oxygen diffusion was significantly suppressed on special boundaries. Metallic Ni was segregated as pure Ni nodules, indicating that the selective oxidation of Cr preferentially occurred. Intergranular oxidation and the resultant embrittlement of the grain boundaries are believed to be major factors affecting the occurrence of intergranular cracking in this alloy. (C) 2016 Elsevier Ltd. All rights reserved