Fatigue-Induced Surface Modification of Zr-Based Metallic Glass under Environmental Conditions.

Metallic glass (MG), an intrinsic heterogeneous structure at the atomic scale, is one of the promising engineering materials with intriguing physical properties. MG often suffers from the fatigue issue caused by the repetitive mechanical loading, but it is still elusive how the local heterogeneity evolves and affects the macroscale fatigue and deformation against bulky external stress. In this study, we investigate the fatigue effect in Zr-Cu-Al ribbon using a bending fatigue method. We used scanning probe microscopy (SPM) in parallel with X-ray diffraction and X-ray photoelectron spectroscopy to figure out the loading effect on the local heterogeneities. The spatially resolved SPM images show that there is a local fluctuation of mechanical and electrical properties on the fatigued side along with morphological deformation compared to the unloaded side. Approaching the broken edge where the fatigue failure occurs, the decaying tendency is not only more dominant but also accelerated by surface oxidation of the fatigued regions. Our study provides a useful guideline on how to monitor structural changes of MGs under fatigue conditions in service and will open a door toward commercialization of high-performance structural engineering materials.

Engineering atomic-level complexity in high-entropy and complex concentrated alloys.

Quantitative and well-targeted design of modern alloys is extremely challenging due to their immense compositional space. When considering only 50 elements for compositional blending the number of possible alloys is practically infinite, as is the associated unexplored property realm. In this paper, we present a simple property-targeted quantitative design approach for atomic-level complexity in complex concentrated and high-entropy alloys, based on quantum-mechanically derived atomic-level pressure approximation. It allows identification of the best suited element mix for high solid-solution strengthening using the simple electronegativity difference among the constituent elements. This approach can be used for designing alloys with customized properties, such as a simple binary NiV solid solution whose yield strength exceeds that of the Cantor high-entropy alloy by nearly a factor of two. This study provides general design rules that enable effective utilization of atomic level information to reduce the immense degrees of freedom in compositional space without sacrificing physics-related plausibility.