Advanced Nanometer Resolution In-Situ Strain Mapping for Metal Oxidation by 4D-STEM

Metal oxidation is a paramount concern in the realm of metal material applications, leading to the degradation of metal surfaces, corrosion, and a decrease in the mechanical properties of the metal. To gain a comprehensive understanding of the strain anisotropy resulting from metal oxidation, the utilization of accurate strain mapping is invaluable, and it enables the advancement of oxidation mechanism theory. Here, we focus on Zr as an illustrative example due to its importance in architecture materials for fuel cladding and developed an in-situ strain mapping method to study the oxidation in metal, by integrating four-dimensional scanning transmission electron microscopy (4D-STEM), advanced gas-cell-holder, precession electron microscopy and direct electron detector. The key to successful strain mapping by our method lies in ensuring high signal-to-noise ratio in the nano-beam electron diffraction patterns. The effect of gas pressure, sample thickness and electron beam precession will be discussed. Our approach facilitates high-quality strain mapping across a large field of view during zirconium oxidation with nanometer resolution. This proposed technique has significant implications for a wide range of corrosion studies, enabling more insights into the chemo-mechanical evolutions in materials under extreme environments.