Mechanical size effects in ZrxNi100−x thin metallic glass films are investigated for thicknesses from 200 to 900nm. Local order, elastic properties and rate sensitivity are shown to be thickness ...independent, while hardness and fracture resistance are not. The increase of hardness with decreasing thickness is related to the substrate constraint on shear banding. Fracture surfaces exhibit a corrugated morphology, except for thickness below 400nm exhibiting perfectly flat surfaces. The corrugations appear again on the thinnest films when adding a cap layer, indicating that the fracture mechanisms are primarily dominated by the loading configuration and geometry which constrain the plastic zone extension. Increasing the Ni content from 25% to 58% leads to an increase of elastic modulus, Poisson ratio, strength, activation volume, and fracture toughness. These changes can be understood based on the change in thermodynamic fragility and Zr–Ni bonds formation. Zr75Ni25 composition shows exceptionally large rate sensitivity exponent equal to 0.058. The fracture mechanisms are not modified by composition and the fracture toughness is systematically low due to the confinement of the plastic zone.
Unlike crystalline metals, which have a well-understood periodical structure, the amorphous structure of metallic glasses (MGs) is still poorly understood, particularly when such a structure ...rearranges itself at the nanoscale under external agitations. In this article, we provide compelling evidence obtained from a recently developed high-resolution atomic force microscopy (HRAFM) technique that reveals the nanoscale structural heterogeneity after thermal annealing in a Zr–Ni metallic glass. Through the HRAFM technique, we are able to uncover the annealing-induced fractal growth of the dense-packing phases in the binary MG thin film, which exhibits a fractal dimension of ∼1.7, in line with a two-dimensional diffusion limited aggregation process. The current findings not only reveal the evolution process of atomic packing in the annealed MG thin film, but also shed light on the possible cooling rate effect on the atomic structure of MGs.
The measurement of the mechanical properties of materials with submicrometer dimensions is extremely challenging, from the preparation and manipulation of specimens to the application of small loads ...and extraction of accurate stresses and strains. A new on-chip nanomechanical testing concept has been developed in order to measure the mechanical properties of submicrometer freestanding thin films allowing various loading configurations and specimen geometries. The basic idea is to use internal stress present in one film to provide the actuation for deforming another film attached to the first film on one side and to the substrate on the other side. The measurement of the displacement resulting from the release of both films gives access to the stress and the strain applied to the test specimen provided the Young's modulus and mismatch strain of the actuator film are known. Classical microelectromechanical-systems-based microfabrication procedures are used to pattern the test structures and release the films from the substrate. The design procedures, data reduction scheme, and a generic fabrication strategy are described in details and implemented in order to build a suite of test structures with various combinations of dimensions. These structures allow the characterization of different materials and mechanical properties and enable high throughputs of data while avoiding any electrical signal or external actuation. Results obtained on ductile aluminum and brittle polysilicon films demonstrate the potential of the method to determine the Young's modulus, yield stress or fracture stress, fracture strain, and strain hardening in ductile materials.
Room-temperature plasticity in metallic glasses (MGs) is commonly associated with local structural heterogeneity; however, direct observation of the subtle structural change caused by plasticity is ...vitally important but the data are extremely scarce. Based on dynamic atomic force microscopy (DAFM), here we show that plasticity-induced structural evolution in a Zr-Ni MG can be revealed via nano-scale viscoelastic contacts between an AFM tip and plastically deformed MG surface layers. Our experimental results clearly show a spatial amplification of the nano-scale structural heterogeneity caused by the distributed plastic flow, which can be linked to the limited growth, reorientation and agglomeration of some nano-scale energy-absorbing regions, which are reminiscent of the behavior of the defect-like regions with non-affine deformation as conceived in many theories and models. Furthermore, we are able to experimentally extract the thermodynamic properties of these nano-scale regions, which possess an energy barrier of 0.3-0.5 eV, about half of that for a typical shear transformation event that usually occurs at the onset of plasticity. The outcome of our current work sheds quantitative insights into the correlation between plasticity and structural heterogeneity in MGs.
Abstract Introduction Eosinophilic angiocentric fibrosis (EAF) is a slowly progressive, benign disease involving the mucosa of the upper airways or, more rarely, the orbit. It belongs to the spectrum ...of IgG4-related disease. Case report The authors report the case of a 61-year-old man who presented with orbital involvement (visual loss, pain, proptosis, and eyelid oedema), headache and nasal obstruction. Imaging revealed a right ethmoido-orbital mass infiltrating the periorbital fat and enveloping the optic nerve. Histological examination concluded on a diagnosis of EAF in the presence of perivascular infiltration by inflammatory cells, predominantly eosinophils, and zones of “onion skin” fibrosis. Immunohistochemistry attributed these lesions to IgG4-related disease. Initial treatment with corticosteroids followed by dapsone failed to control the disease and resulted in severe steroid dependence. Surgical ethmoidectomy with resection of the lamina papyracea was performed to allow displacement of the eyeball into the nasal cavity in the event of another episode. Discussion The combination of surgery and rituximab achieved lasting pain relief with no recurrence of exophthalmos.
In this article, we discuss the recent use of the high-resolution dynamic atomic force microscopy (DAFM) in mapping the nano-scale dynamical structural heterogeneity in thin film metallic-glasses ...(TFMGs). Our focus is laid on the major factors which can influence the structural contrast in the DAFM images, such as tip radius, free-amplitude, set-point amplitude and surface roughness. Finally, through a comparative study of different TFMGs and single-crystal silicon, we demonstrate that the DAFM technique is effective in distinguishing different nanostructures through their energy dissipation spectra.
•Obtaining the structural image requires adjusting the free amplitude.•Obtaining the structural image requires adjusting the set-point amplitude.•Obtaining the structural image demands a smooth surface.•The obtained structural image is tip radius dependent.•The obtained structural images can distinguish different nanostructures.
The crystallization kinetics of Cu38Zr46Ag8Al8 bulk metallic glass in non-isothermal mode and isothermal mode are investigated by differential scanning calorimetry. In non-isothermal conditions, the ...average value of activation energy is determined by Kissinger equation, and the value is around 310kJ/mol. The crystallization enthalpy is about 28.69J/g. In addition, the local Avrami exponent is adopted to describe the crystallization process. In isothermal route, the average value of activation energy for crystallization is calculated by the Arrhenius equation, and the value is about 451kJ/mol. The crystallization enthalpy is about 1.63J/g. And the Avrami exponent n ranges from 4.10 to 4.74, which indicates that the crystallization mechanism is mainly governed by constant nucleation rate. The created phases in the two conditions are different which can be confirmed by the X-ray diffraction test, this result is in accordance with the different crystallization enthalpies, but it's different with other investigations.
•The crystallization phases of Cu38Zr46Ag8Al8 are different in isothermal and non-isothermal conditions.•The activation energy in isothermal conditions is about 451kJ/mol; the crystallization enthalpy is about 1.63J/g.•The activation energy in non-isothermal conditions is about 310kJ/mol; the crystallization enthalpy is about 28.69J/g.•The created phases are different due to the different heating conditions.
We conducted a single-center retrospective study to compare patient characteristics and death rates during the Omicron (O, December 01, 2021, to September 30, 2022) and pre-Omicron (PO, March 01, ...1920, to October 31, 2021) periods.
We retrospectively analyzed the data of 2932 patients (1242 (O) and 1690 (PO)) hospitalized (>24 h) with laboratory-confirmed COVID.
Compared to the PO period, O period patients were less frequently men, had a lower body mass index and fewer comorbidities except for immunosuppression and pregnancy. Nosocomial COVID-19 accounted for 18.2 % (O) and 15.4 % (PO) of cases (p = 0.05). Patient mortality rates during the O and PO periods were 11.0 % and 16.9 % (p < 0.001), respectively. Unvaccinated status (p < 0.001), existence of comorbidities, (p < 0.001) and high LDH value at baseline (p = 0.015), but not the period, were identified as factors likely to explain death.
During the Omicron period, the inpatient death rate remained > 10 %, especially among unvaccinated and comorbid patients. Nosocomial cases were more frequent.
The deformation at high temperature of a La60Ni15Al25 bulk metallic glass has been investigated. In the experimental domain in which homogeneous deformation could be obtained, activation energies in ...agreement with what is usually measured for metallic glasses with similar glass transition temperatures were identified but particularly large values of activation volumes were measured. Such values of activation volumes were attributed to the pronounced secondary relaxation displayed by the investigated glass, suggesting the existence of structural heterogeneities in the microstructure.
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