Mitigating relaxation-induced embrittlement in metallic glasses with multi-component microalloying

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

Manipulation of relaxation processes in a metallic glass through cryogenic treatment

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

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

Unraveling the microstructural heterogeneity and plasticity of Zr50Cu40Al10 bulk metallic glass by nanoindentation

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.

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.

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

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.

Effect of ion irradiation in an Al90Fe2Ce8 metallic glass

Effect of enthalpy relaxation rejuvenation on microstructure and corrosion resistance of a Zr-based bulk metallic glass

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.

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.