Leonardo Agudo Jácome

In the present work, we use electron backscatter diffraction (EBSD) in the scanning electron microscope (SEM) to study the evolution of local misorientations in the γ / γ ′ microstructure of a single‐crystal Ni‐based superalloy after exposures to creep conditions in the high temperature and low stress field. Sampling fields of statistically relevant dimensions were evaluated (16 × 12 µm ² , corresponding to almost 1000 γ′ particles in the initial state). We apply a new method that allows for differentiation between diffraction signals from γ and γ′ phase regions. The spatial relationships between locations where misorientation accumulation occurs are investigated for dendritic and interdendritic regions loaded along the [001] and [110] crystallographic directions. Increases in intra‐ and interphase misorientation are observed as dislocation density increases, then saturates. The higher dislocation densities in γ channels than in γ ′ particles seen by transmission electron microscopy are shown to be statistically stored on the micron size scale. Geometrically necessary misorientations are observed to cancel each other out over the macroscopic scale, resulting in no detectable macroscopic change in crystal orientation for total accumulated plastic strains of 6%. The limitations of the methods are discussed, and areas in need of further work are highlighted.

This study extends the findings of Cao et al. (2020) on the creep rupture behavior of circular double‐notch tensile (CDNT) specimens of the Ni‐base superalloy single‐crystal ERBO‐1, where a triaxial stress state governs. Additional creep tests are conducted at 950 °C and 400 MPa on specimens loaded in [001], [110], and [111] directions and interrupted after 80 h. Complementary characterization methods, including electron backscattered diffraction, focused ion beam‐scanning electron microscopy tomography, scanning transmission electron microscopy, and microcomputed tomography, were used to study the formation of topologically close‐packed phase (TCP)‐phase particles and micropores. Early creep failure of the [110] specimen is caused by a critical alignment of micropores, a higher resolved shear stresses acting on a higher number of dislocations in the γ and γ′ phases, and higher volume fraction of TCP‐phase particles. After 80 h, the [111] specimen shows significantly more localized deformation and a 1.4 times higher displacement than the [001] and [110] specimens. The [110] specimen shows distinct local misorientations from the mean orientation of the order of up to 2°. The findings provide a deeper understanding of the microstructural factors that influence creep behavior and rupture life in CDNT specimens of single‐crystal Ni‐base superalloys.

Lithium isotopic fractionation is well-established in dynamic geochemical systems; however, its role in lithium-ion batteries (LIBs) remains uninvestigated. Herein, we report the first depth-resolved demonstration that isotopic separation occurs during Li-ion cell operation whose magnitude depends on the cycling history. Using depth-resolved glow discharge mass spectrometry, we monitored the 7Li/6Li ratio in LiNi0.333Mn0.333Co0.333O2 (NMC111)||graphite coin cell electrodes at defined life-cycle stages. Different charging rates were examined to get mechanistic insight into kinetic and thermodynamic control in the fractionation process. Although pristine electrodes exhibit a uniform isotopic ratio, cycled electrodes show a distinct 7Li enrichment in the positive electrode and a corresponding accumulation of 6Li at the surface of the negative electrode. The degree of isotopic separation varies with the charging rate. Isotopic signatures correlate with capacity fading, indicating lithium isotope mapping as a sensitive diagnostic tool for tracking electrode degradation and the evolution of the electrode–electrolyte interphases in LIBs.

We measure the electron beam-induced current to analyze the electron-induced secondary electron (SE) emission from micron-sized gold particles illuminated by 80 and 300 keV electrons in a transmission electron microscope. A direct comparison of the experimental and simulated SE emission (SEE) employing Monte Carlo scattering simulations based on the GEANT4 toolkit yields overall good agreement with a noticeable discrepancy arising from the shortcoming of the GEANT4 scattering cross sections in the low-loss regime. Thus, the electron beam-induced current analysis allows to quantify the inelastic scattering including SEE in the transmission electron microscope and provides further insight into the charging mechanisms.