Localized attack of a two-phase metal, scanning electrochemical microscopy studies of NiCrMoGd alloys

In this paper, the corrosion of a two-phase alloy, NiCrMoGd, was studied using scanning electrochemical microscopy (SECM). This alloy was developed as a neutron-absorbing alloy for use in nuclear waste storage applications. Gadolinium, the neutron-absorbing element, forms a secondary Ni5Gd eutectic phase, referred to as the gadolinide phase. This phase is preferentially attacked in halide-containing solutions, resulting in dissolution of the surface exposed gadolinide phase. SECM was used to image the attack of these micrometer-scale particles. The surface activity decreases following the dissolution of the gadolinide particles, which is due to the passive nature of the NiCrMo base alloy. Evidence of a coupled mechanism was observed, where the chemistry of a dissolving particle influences the stability of neighboring particles. This alloy serves as a useful system for studying the effect of localized chemistry developed at a dissolving pit on neighboring surfaces, which is a phenomenon that is inferred but not well understood.