AVS 52nd International Symposium
    Applied Surface Science Monday Sessions
       Session AS-MoA

Paper AS-MoA7
In-Situ and Ex-Situ Characterization of the Electrochemically-Accelerated Corrosion of Ni-Cr-Mo-Gd Alloy Surfaces in Aqueous Media

Monday, October 31, 2005, 4:00 pm, Room 206

Session: Electron Spectroscopies
Presenter: T.L. Trowbridge, Idaho National Laboratory
Authors: P.J. Pinhero, Idaho National Laboratory
T.E. Lister, Idaho National Laboratory
R.E. Mizia, Idaho National Laboratory
T.L. Trowbridge, Idaho National Laboratory
A.W. Glenn, Idaho Completion Project
Correspondent: Click to Email
A new thermal-neutron-absorbing structural Ni-Cr-Mo-Gd alloy was developed at the Idaho National Laboratory (INL). The purpose of this alloy is to potentially absorb neutrons liberated from spent nuclear fuel (SNF) and mitigate any issues related to nuclear criticality. The microstructure of this alloy indicates a two-phase structure consisting of the primary Ni-Cr-Mo austenite matrix phase and secondary Ni@sub 5@Gd phase inclusions arising from the precipitation of the austenite-insoluble Gd. Presently, this alloy is under consideration for use within the U.S. Department of Energy (DOE) standardized SNF waste packages. To support the case for this alloy's acceptance and understand its more fundamental surface character, studies were undertaken to examine its structure and composition with respect to its bulk properties, the role of oxidation and resulting passivation on its susceptibility to corrode, and finally how these properties are influenced through boron-doping. This paper focuses on the susceptibility of the Ni-Cr-Mo-Gd surface to corrode. Scanning electrochemical microscopy (SECM) was used to examine localized corrosion of the surface in situ. It was observed that the corrosion initiates at the interfaces between the Ni@sub 5@Gd particles and the surrounding austenite matrix. Corrosion then propagates such that these particles completely dissolve, leaving an intact "passive" Ni-Cr-Mo surface. Current-sensing atomic force microscopy (CS-AFM) images help support the argument of electron transfer initiating at the interface formed between the included particles and the austenite matrix. Ex situ analysis using focused ion beam / scanning electron microscopy (FIB/SEM), scanning Auger microscopy (SAM), and x-ray photoelectron microscopy show how the structure and surface composition change as a function of the electrochemically driven corrosion process.