  Corrosion is a major concern for many industries, as corrosive environments
can induce structural and morphological changes that lead to material
dissolution and accelerate material failure. The progression of corrosion
depends on nanoscale morphology, stress, and defects present. Experimentally
monitoring this complex interplay is challenging. Here we implement in situ
Bragg coherent X-ray diffraction imaging (BCDI) to probe the dissolution of a
Co-Fe alloy microcrystal exposed to hydrochloric acid (HCl). By measuring five
Bragg reflections from a single isolated microcrystal at ambient conditions, we
compare the full three-dimensional (3D) strain state before corrosion and the
strain along the [111] direction throughout the corrosion process. We find that
the strained surface layer of the crystal dissolves to leave a progressively
less strained surface. Interestingly, the average strain closer to the centre
of the crystal increases during the corrosion process. We determine the
localised corrosion rate from BCDI data, revealing the preferential dissolution
of facets more exposed to the acid stream, highlighting an experimental
geometry effect. These results bring new perspectives to understanding the
interplay between crystal strain, morphology, and corrosion; a prerequisite for
the design of more corrosion-resistant materials.
