Inherent structure length in metallic glasses: simplicity behind complexity.

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

Material genetic engineering can significantly accelerate the development of new materials. As an important topic in material science and condensed matter physics, the development of metallic glasses (MGs) with specific properties has largely been the result of trial and error since their discovery in 1960. Yet, property design based on the physical parameters of constituent elements of MGs remains a huge challenge owing to the lack of an understanding of the property inheritance from constitute elements to the resultant alloys. In this work, we report the inherent relationships of the yield strength σ y, Young’s modulus E, and shear Modulus G with the valence electron density. More importantly, we reveal that the electronic density of states (EDOSs) at the Fermi surface (E F) is an inheritance factor for the physical properties of MGs. The physical properties of MGs are inherited from the specific element with the largest coefficient of electronic specific heat (γi ), which dominates the value of the EDOS at E F. This work not only contributes to the understanding of property inheritances but also guides the design of novel MGs with specific properties based on material genetic engineering.

Manipulation of relaxation processes in a metallic glass through cryogenic treatment

New ductile laminate structure of Ti-alloy/Ti-based metallic glass composite with high specific strength

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

Effects of minor alloying on the mechanical properties of Al based 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.

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

The mechanical properties of materials are fundamentally determined by the behavior of atomic bonds under stress. Probing bond behavior during deformation, however, is highly challenging, particularly for materials with complex chemical compositions and/or atomic structures, such as metallic glasses (MGs). As a result, a significant gap exists in the current understanding of the mechanical properties of MGs in relation to the atomic bond behavior and how this relationship is influenced by metallurgical factors (e.g., alloy composition, processing conditions). Here, we present our study of the compositional effects on the tensile behavior of atomic bonds in Cu93−xZrxAl7 (x = 40, 50, 60 at.%) MGs using large-scale molecular dynamics (MD) simulations and statistical analysis. Specifically, we examine the populations (fractions), mean bond lengths, mean bond z-lengths, and mean bond z-strains of the different bond types before and during tensile loading (in the z-direction), and we compare these quantities across the different alloy compositions. Among our key findings, we show that increasing the Zr content in the alloy composition leads to shortened Zr-Zr, Al-Cu, Al-Zr, and Cu-Zr bonds and elongated Cu-Cu bonds, as evidenced by their mean bond lengths. During deformation, the shorter Zr-Zr bonds and longer Cu-Cu bonds in the higher-Zr-content alloys, compared with those in the x = 40 alloy, appear stronger (more elastic stretching in the z-direction) and weaker (less z-stretching), respectively, consistent with general expectations. In contrast, the Al-Cu, Al-Zr, and Cu-Zr bonds in the higher-Zr-content alloys appear weaker in the elastic regime, despite their shortened mean bond lengths. This apparent paradox can be reconciled by considering the fractions of these bonds associated with icosahedral clusters, which are known to be more resistant to deformation than the rest of the glassy structure. We also discuss how the compositional effects on the bond behavior relate to variations in the overall stress–strain behavior of the different alloys.

Metallic glasses (MGs) are susceptible to embrittlement due to structural relaxation. Microalloying has been explored as a strategy to improve the mechanical properties of MGs. Here it is shown that microalloying with several elements can mitigate embrittlement due to relaxation and even increase plasticity in annealed states. Changes in the glass states with relaxation were studied using X-ray diffraction and differential scanning calorimetry. The mechanical properties of the as-cast and relaxed states were characterised by macroscopic mechanical testing, microindentation, and nanoindentation. Relaxed samples with improved plasticity show more shear events and lower propagation velocities during indentation. Transmission electron microscopy micrographs showed no evidence of crystallization in the annealed samples, suggesting the improvements are due to structural features of the glassy state. This microalloying approach should translate to other alloy systems and aid the wider use of MGs.

Metallic glasses represent an interesting group of materials as they are superior in certain mechanical properties, i.e. they reach near theoretical strength, exhibit large elastic strain (2 %) and low elastic modulus compared to their crystalline counterparts. The discovery of new alloy compositions solidifying into bulk glassy samples allows for conventional mechanical characterization and raises the hope for possible applications as structural material. In order to improve and tailor the mechanical properties, composite materials have been developed that consist of a glassy matrix with second phase dispersions of different chemical compositions, morphology, and different length scale. This article reviews the different processing routes, the evolution of different microstructures and the resulting elastic and plastic properties of metallic glasses and their composites. Additionally, the recently reported monolithic ductile bulk metallic glasses will be discussed in terms of their structure, chemical composition and their unique “work hardening”‐like behavior.

Owing to the unique properties, such as excellent mechanical performance, and nano-scale surface roughness, metallic glass can be applied in various novel fields. Meanwhile, the improvement of thermal stability and hardness is the common target in these applications. Minor alloying is an effective method to enhance the thermal and mechanical properties of metallic glasses. Different from elements used to be doped into metallic glass, the role nitrogen atoms play in metallic glass is quite distinct and critically important, owing to its strong electronegativity and small atomic radius. In this work, an alternative class of metallic glass is developed. By adding nitrogen into Zr-Cu-Al-Ag TFMG, the configuration energy of short range structure is greatly modified. From the viewpoint of thermal behavior, the evolution of Tg and elastic modulus with nitrogen could be well correlated, implying significant effect of nitrogen atoms on the potential energy landscape (PEL) of the TFMGs. Besides, more amounts of nitrogen addition lead to the increase of short range order structure in the amorphous matrix. That is, most metallic atoms are strongly attracted by nitrogen, forming the nitrogen-centered cluster, in which more energy is required to cause plastic deformation. On the other hand, a meta-stable state with lower energy is attained as indicated by the much higher Tx than normal Zr-based metallic glasses. However, the amorphicity region of nitrogen in Zr-Cu-Al-Ag metallic glass is not wide enough, restricting the enhancement amount of thermal and mechanical performances. By incorporating Ta firstly, the competing ZrN crystalline phase is destabilized, leading to the wider amorphicity region of nitrogen in Ta-Zr-Cu-Al-Ag TFMG. As a result, hardness over 10 GPa, Tg near 800 K, and supercool liquid region as wide as 112K is achieved in the nitrogen-doped Ta-Zr-Cu-Al-Ag TFMG.

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.

The widespread enthusiasm for research on bulk metallic glasses is driven by both a fundamental interest in the structure and properties of disordered materials and their unique promise for structural and functional applications. Unlike the case for crystalline materials, the disordered and nonequilibrium nature of metallic glasses causes their underlying deformation mechanisms to be poorly known. A definite correlation between mechanical behavior and the atomic/electronic structures of metallic glasses has not been established. In this article, I focus on the micromechanisms of mechanical behavior of metallic glasses and present a brief overview of the current understanding of their strength, ductility, and plasticity at the microscopic and atomic scales. The important factors that control the mechanical behavior of metallic glasses are outlined on the basis of recent theoretical and experimental findings. The outstanding issues highlighted in this review are expected to be important for future research on the mechanical properties of metallic glasses.

Effect of ion irradiation in an Al90Fe2Ce8 metallic glass