Jason R. Trelewicz

Amorphous grain boundary complexions have been shown to be radiation tolerant interfaces that can also reduce grain boundary embrittlement, marking them as favorable microstructural features. However, the incorporation of these features into new alloy systems is often a slow and arduous process based on trial and error. Here, a computational framework for alloy design is presented, which enables the selection of dopants that promote the formation of amorphous grain boundary complexions. This framework is primarily built on density functional theory calculations and is demonstrated for W-rich binary and ternary alloys, which represent a promising target for fusion energy materials. Our framework first evaluates the grain boundary segregation tendency of dopants and then the energy penalty for amorphization alongside targeted interfacial energy comparison, with the end goal of identifying the best dopants. For a W base, Y and some transition metals such as Co and Ni are found to significantly lower these energetic barriers. Electronic structure analysis, local lattice distortion, and charge density distributions are calculated and used to provide mechanistic explanations for these dopant selections. Finally, the framework is validated by comparing with experimental literature for W alloys and a refractory complex concentrated alloy, showing a strong correlation between our dopant selections and low sintering onset temperatures that have been attributed to activated sintering. As a whole, this work establishes a transferable pipeline for designing alloys with grain boundary complexions across diverse alloy systems.

Ceramic oxides offer a range of advantageous characteristics for withstanding intense mixed radiation fields, and consequently, interest has grown in exploring their behavior for nuclear applications such as fuel matrices and waste forms. In this study, magnesium oxide (MgO) was irradiated with ions of varying species, energies, and fluences, and the resulting structural modifications were characterized using synchrotron-based x-ray diffraction (XRD) combined with grazing-incidence XRD. Across all irradiation conditions, unit-cell expansion was observed, increasing with fluence. The magnitude of expansion was most significant for ions that primarily lose energy through nuclear interactions and lowest for those dominated by electronic excitations, spanning nearly two orders of magnitude. Under highly ionizing conditions, lattice swelling was reduced, but microstrain accumulation was enhanced, suggesting that defects are more localized and contribute less to long-range structural changes. These findings reveal the distinct roles of nuclear and electronic energy loss in defect formation and provide mechanistic insight into radiation-induced modifications in MgO, with implications for the design of radiation-tolerant materials for advanced nuclear technologies. Finally, the framework we present—incorporating an irradiation matrix that spans both nuclear and electronic energy loss dominated regions, strengthened by advanced quantitative XRD characterization—is widely applicable to the study of defect physics in polycrystalline materials.

The accumulation of helium bubbles at grain boundaries (GBs) critically degrades the mechanical integrity of structural materials in nuclear reactors. While GBs act as sinks for radiation-induced defects, their inherent structural anisotropy leads to complex helium bubble evolution behaviors that remain poorly understood. This work integrates accelerated molecular dynamics simulations and a novel atomic-scale metric, the flexibility volume (V_f), to establish the interplay between GB character, helium segregation, and bubble growth mechanisms in body-centered cubic iron. We demonstrate that V_f, which incorporates both local atomic volume and vibrational properties, qualitatively predicts deformation propensity. Our results reveal that the atomic-scale segregation energy landscape dictates initial helium clustering and subsequent bubble morphology, with low-energy channels in tilt Σ5 boundary facilitating one-dimensional migration while isolated deep traps in twist Σ13 boundary promote larger, rounder bubble morphology. Critically, besides gradual bubble growth via trap mutation mechanism, we identify two distinct stress-relief mechanisms: loop punching in anisotropic tilt Σ5 boundary and interfacial decohesion in twist Σ11 boundary, with the dominant pathway determined by the interplay between bubble morphology and local mechanical softness. This study establishes a fundamental connection between GB crystallographic and energetical anisotropy and helium bubble evolution, providing critical insights for designing radiation-tolerant microstructures.