Bragg Coherent Diffraction Imaging of Metal Microcrystals Using a Multipurpose In Situ Cell Design

Abstract

Structural materials are a key limiting factor in the safety, longevity, and efficiency of nuclear power plants. Advanced metal alloys show great promise for use in reactor environments, but ensuring their reliability requires a fundamental understanding of their microstructural evolution under extreme conditions. In situ X-ray experiments offer a powerful means to investigate nanoscale defect evolution under reactor-relevant conditions. Bragg coherent diffraction imaging (BCDI), a synchrotron X-ray technique, enables high-resolution 3D imaging of degradation processes. Combined with an experimental electrochemical cell, BCDI is a promising tool for providing insight into the problems facing advanced materials in next-generation reactor designs. In this work, a custom designed electrochemical cell, successfully adapted for use at four beamlines, was developed and used to demonstrate in situ corrosion and hydrogen embrittlement (HE) of nickel (Ni) and copper (Cu) microcrystals. HE experiments confirmed the hydrogen evolution reaction (HER) at Cu surfaces and bulk embrittlement, using a removable silver/silver chloride (Ag/AgCl) electrode to maintain a stable reference potential. The cell’s chemical durability was demonstrated during more than 30 hours of operation, wherein Ni microcrystals were subjected to boric acid (B(OH)3) and lithium hydroxide (LiOH) to simulate the corrosive coolant chemistry of pressurized water reactors (PWRs). BCDI revealed the evolution of phase and dislocations in a Ni microcrystal under these conditions, affirming its power as a nanoscale measurement tool. Furthermore, BCDI provided direct evidence of lattice expansion in Cu in response to cathodic reduction of hydrogen. Additional analysis reveals a selective beam relaxation effect on Ni microcrystals, providing further insight into radiation-material interactions. The findings of this work lay important groundwork for future advanced alloy development utilizing user-friendly in situ experimental cells.