Inheritance factor on the physical properties in metallic glasses

One of the central themes in materials science is the structure-property relationship. In conventional crystalline metals, their mechanical behaviour is often dictated by well-defined structural defects such as dislocations, impurities, and twins. However, the structure-property relationship in amorphous alloys is far from being understood, due to great difficulties in characterizing and describing the disordered atomic-level structure. Herein, we report a universal, yet simple, correlation between the macroscopic mechanical properties (i.e., yield strength and shear modulus) and a unique characteristic structural length in metallic glasses (MGs). Our analysis indicates that this characteristic length can incorporate effects of both the inter-atomic distance and valence electron density in MGs, and result in the observed universal correlation. The current findings shed lights on the basic understanding of mechanical properties of MGs from their disordered atomic structures.

Metallic glasses are one of the most interesting mechanical materials studied in the last years, but as amorphous solids, they differ strongly from their crystalline counterparts. This matter can be addressed with the development and application of predictive techniques capable to describe the plastic regime. Here, machine learning models were employed for the prediction of plastic properties in CuZr metallic glasses. To this aim, 100 different samples were subjected to tensile tests by means of molecular dynamics simulations. A total of 17 materials properties were calculated and explored using statistical analysis. Strong correlations were found for stoichiometry, temperature, structural, and elastic properties with plastic properties. Three regression models were employed for the prediction of six plastic properties. Linear and Ridge regressions delivered the better prediction capability, with coefficients of determination above sim80% for three plastic properties, whereas Lasso regression rendered lower performance, with coefficients of determination above sim60% for two plastic properties. Overall, our work shows that molecular dynamics simulations together with machine learning models can provide a framework for the prediction of plastic behavior of complex materials.

Tunable elastic heterogeneity caused by deformation-induced magnetization in flexible metallic glass

Metallic glass is a promising metallic material with many unique properties, and also considered as a model system to study the mysteries of amorphous materials. Recently, many experimental and simulation results supported the existence of “flow unit” in metallic glass. In this paper, we review the background, the theoretical and experimental evidences of flow unit model. Flow units are considered as those loosely packed regions embedded inside the elastic matrix and behave like viscous liquid. Compared with the matrix, flow unit regions have low modulus and strength, low viscosity, high atomic mobility and stand in the saddle points on energy landscape. Therefore, flow units can be treated as dynamical defects in metallic glass. The feature, activation and evolution process of flow unit region in metallic glass as well as their correlation with property in metallic glass are also reviewed. Through dynamical mechaincal methods like dynamical mechanical spectra and stress relaxation, flow unit region and its properties can be distinguished and studied. A three-parameter physical model is proposed to describe the mechnical behaivors of flow units. The activations and evolutions of flow unit under different temperature and strain conditions are studied. A three-stage evolution process is found and the relation with mechanical performance and relaxation behavior is established. The characteristics of flow units are also related to various properties of metallic glass, like plasticity, strength, fracture and boson peaks. By using the thermal, mechanical and high pressure aging procedues, the properties of metallic glass can be manipulated as desired through adjusting the density of flow units. We show that the flow unit model not only helps to understand the mechanism behind many long-standing issues like deformation, glass transition dynamic relaxations, and the connection between strucutre and properties and performance of metallic glasses, but also is crucial for tuning and designing the properties of metallic glasses.

Metallic glasses (MGs), as new disordered materials prepared by rapidly quenching melted alloys, have attracted tremendous attention in the material science community. Due to their long-ranged disorderd and short-ranged ordered structures, MGs usually exhibit uniquely physical, chemical and mechanical properties, which give rise to promising applications in many fields, and especially they are expected to be potentially structural materials used in irradiation conditions, such as in nuclear reactors and aerospace.In this paper, the effects of ion irradiation on the microstructure, mechanical properties, physical, and chemical properties of MGs are reviewed. It is found that the effects of ion irradiation on the microstructures and mechanical properties depend on the ion energy as well as the composition of MG. When high energy ions interact with a solid, the collisions take place between the incident ions and atoms of the solid, which are dominated by inelastic processes (electronic stopping) and elastic processes (nuclear stopping). The inelastic processes result in the excitation and ionization of substrate atoms. In contrast, the elastic processes lead to ballistic atomic displacements. Nuclear stopping can produce structure defects and irradiation damage in glassy phase. The collisions between the incident ions and the target atoms in MGs can cause the target atoms to deviate from their original positions, and leave a large number of vacancies and interstitial atoms behind. The separations between the vacancies and the interstitial atoms form displacement cascades. The interstitial atoms with a low kinetic energy can transfer self-energies to thermal energies, resulting in a thermal spike due to the accumulation of a large quantity of the thermal energies from interstitial atoms. Such a thermal spike will cause MGs to melt and resolidify, which therefore makes the structure of glassy phase changed. Furthermore, the ion irradiation can modify the structures of MGs by introducing excessive free volumes and promoting the mobilities of atoms, which leads to the dilatation of the glassy phase and nanocrystallization. The increase of free volumes softens the MGs, and then causes the plastic deformation mechanism to transform from a heterogeneous deformation to a homogeneous deformation, which significantly enhances the plastic deformation ability.This review paper can not only improve the understanding of the relationship between microstructure evolution and macroscopic mechanical properties, and provide an experimental and fundamental basis to understand the deformation mechanism of MGs, but also summarize the performances of MGs under high dosage of ion irradiation. Moreover, it is of fundamental and practical importance for engineering applications of such advanced materials.

Tailoring microstructure of metallic glass for delocalized plasticity by pressure annealing: Forward and inverse studies

Bicontinuous Nanoporous Design Induced Homogenization of Strain Localization in Metallic Glasses

Effects of minor alloying on the mechanical properties of Al based metallic glasses

Stability of metallic glasses under simulated space conditions

Structure, defects and properties of metallic glasses

Widespread adoption of metallic glasses (MGs) in applications motivated by high strength and elasticity combined with plastic-like processing has been stymied by their lack of tensile ductility. One emerging strategy to couple the attractive properties of MGs with resistance to failure by shear localization is to employ sub-micron sample or feature length scales, although conflicting results shroud an atomistic understanding of the responsible mechanisms in uncertainty. Here, we report in situ deformation experiments of directly moulded Pt57.5Cu14.7Ni5.3P22.5 MG nanowires, which show tunable tensile ductility. Initially brittle as-moulded nanowires can be coerced to a distinct glassy state upon irradiation with Ga+ ions, leading to tensile ductility and quasi-homogeneous plastic flow. This behaviour is reversible and the glass returns to a brittle state upon subsequent annealing. Our results suggest a novel mechanism for homogenous plastic flow in nano-scaled MGs and strategies for circumventing the poor damage tolerance that has long plagued MGs.

The metallic glasses are known as amorphous and metastable materials. These materials have superior mechanical properties over crystalline materials with the same chemistry. Continuous efforts were made to improve the properties of metallic glass. The severe plastic deformation (SPD) method is used to improve the ductility of the glass. SPD causes the deformation at the atomic level in the disordered structure of the glass. Many methods are reported, such as cryogenic cycling, high-pressure torsion, and equal channel angular pressing, which are used for the SPD. In recent works on nanostructured metallic glasses, it has been evidenced that some properties, for example, mechanical, thermal, and magnetic, have improved compared to the bulk metallic glass. This paper has reviewed the recent progress in the SPD of the bulk and nanostructured metallic glasses. Different methods for the SPD have been addressed here. The effect of SPD on the properties of metallic glass is deliberated in this paper. Moreover, the challenging tasks of deformation occurrence in the glass and its characterization were considered, trying to develop a sound understanding of SPD in bulk and nanostructured metallic glasses.

First principles study of three dimensional topological phases of GdxY1−xPtBi (x=0, 0.25, 0.5, 0.75, 1) alloys

Workflow for a reproducible and accurate determination of free volume in metallic glasses by differential scanning calorimetry

Toward atomic-scale understanding of structure-dynamics-properties relations for metallic glasses