Viscous surface flow induced on Ti-based bulk metallic glass by heavy ion irradiation

Ti-based bulk metallic glass was irradiated by a 20 MeV Cl4+ ion beam under liquid-nitrogen cooling, which produced remarkable surface smoothing and roughening that respectively correspond to normal and off-normal incidence angles of irradiation. Atomic force microscopy confirms two types of periodic ripples distributed evenly over the rough glass surface. In terms of mechanism, irradiation-induced viscosity agrees with the theoretical prediction for metallic glasses near glass transition temperature. Here, a model is introduced, based on relaxation of confined viscous flow with a thin liquid-like layer, that explains both surface smoothing and ripple formation. This study demonstrates that bulk metallic glass has high morphological instability and low viscosity under ion irradiation, which assets can pave new paths for metallic glass applications. (C) 2016 Published by Elsevier B.V.</p

9/4/25, le ministre de Portugal [M. Antonio da Fonseca] au [tombeau du] soldat inconnu : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 99804Appartient à l’ensemble documentaire : Pho20RolImage de press

Serrated Flow and Shear Band Evolution in A Zr-Based Bulk Metallic Glass After Plastic Deformation and Annealing

The effect of pre-deformation and annealing on serrated plastic flow and shear band features of a Zr-based bulk metallic glass was investigated through nanoindentation and macroindentation tests. The results showed that the serrated plastic flow during the loading process of nanoindentation was significantly suppressed in pre-deformed sample and re-appeared after subsequent annealing. The effect of pre-existed shear bands on the development of final shear bands was characterized by macroindentation without bonded interfaces. Pre-deformation does not lead to the multiply of shear band during the consequent plastic deformation, but decrease the shear band number significantly. The change in plastic flow behavior of the alloy by pre-deformation is thought to be the preferential propagation of existed shear bands, and its effect can be eliminated by annealing below glass transition temperature. (C) 2010 Elsevier B.V. All rights reserved

Study on Crystallization Kinetics of Binary Alloys Through Model Colloidal Mixtures

Since the discovery of amorphous alloys, extensive attentions have been paid to understand the mechanism of glass-forming. The structural studies on its underlying mechanism have met challenge on direct structural characterization. It has been shown that the phase behavior of colloids dispersed in a solvent is thermodynamically equivalent to that of atoms and small molecules, however, colloids can be studied with optical microscopy due to their relatively large size. In this work, we use a binary colloidal model system with the particle size ratio comparable to atomic ratio of reported binary bulk metallic glasses to study the topological effect on crystallization and glass-forming ability of binary metallic alloys (Cu-Hf and Cu-Zr systems). The crystallization kinetics and structure of the colloid system were studied by real-time optical examination and light scattering technique. The results exhibit that there are two confined regions in the mixing ratio (composition) range in the colloid system with an enhanced glass-forming ability and retarded crystallization kinetics. The agreement between results of the model system and the experimental data on the binary bulk metallic glass formation suggests that purely topological factor plays an important role in determining the glass-forming ability. (C) 2010 Elsevier B.V. All rights reserved

Anomalous shear band characteristics and extra-deep shock-affected zone in Zr-based bulk metallic glass treated with nanosecond laser peening

The effects of nanosecond laser peening on Zr41Ti14Cu12.5Ni10Be22.5 metallic glass were investigated in this study. The peening treatment produced an extra-deep shock-affected zone compared to crystal metal. As opposed to the conventional shear bands numerous arc shear bands appeared and aggregated in the vertical direction of the laser beam forming basic units for accommodating plastic deformation. The arc shear bands exhibited short and discrete features near the surface of the material then grew longer and fewer at deeper peened layer depths which was closely related to the laser shock wave attenuation. An energy dissipation model was established based on Hugoniot Elastic Limit and shear band characteristics to represent the formation of an extra-deep shock-affected zone. The results presented here suggest that the bulk modification of metallic glass with a considerable affected depth is feasible. Further they reveal that nanosecond laser peening is promising as an effective approach to tuning shear bands for improved MGs ductility.</p