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Abstract Understanding the atomistic mechanisms of inelastic deformation in metallic glasses (MGs) remains challenging due to their amorphous structure, where local carriers of plasticity cannot be easily defined. Using molecular dynamics (MD) simulations, we analyzed the onset of inelastic deformation in CuZr MGs, specifically the temperature dependence of the elastic limit, in terms of localized shear transformation (ST) events. We find that although the ST events initiate at lower strain with increasing temperature, the elastic limit increases with temperature in certain temperature ranges. We explain this anomalous behavior through the framework of an energy-strain landscape (ESL) constructed from high-throughput strain-dependent energy barrier calculations for the ST events identified in the MD simulations. The ESL reveals that the anomalous behavior is caused by the transition of ST events from irreversible to reversible with increasing temperature. An analytical formulation is developed to predict this transition and the temperature dependence of the elastic limit.

The interfacial energies between a eutectic Ga–In–Sn liquid alloy and single nanoscopic asperities of SiOx, Au, and PtSi have been determined in the temperature range between room temperature and 90 °C by atomic force spectroscopy. For all asperities used here, we find that the interfacial tension of the eutectic Ga–In–Sn liquid alloy is smaller than its free surface energy by a factor of two (for SiOx) to eight (for PtSi). Any significant oxide growth upon heating studied was not detected here, and the measured interfacial energies strongly depend on the chemistry of the asperities. We also observe a weak increase of the interfacial energy as a function of the temperature, which can be explained by the reactivity between SiOx and Ga and the occurrence of chemical segregation at the liquid alloy surface.

Materials with controlled structural gradient have gained attention due to their unique combinations of properties. Here the authors report strategies to design controllable gradients in bulk metallic glasses, demonstrating extra plasticity and suppression of shear localization.

The high-temperature tensile deformation behaviors of the recrystallization annealed Al7(CoNiV)93 medium entropy alloy with a duplex hierarchical microstructure of face-centered cubic (fcc) and ordered body-centered cubic L21 Heusler-type grains were investigated. The alloy showed a remarkably high tensile strength of ∼1.1 GPa and good ductility of ∼17% at 923 K due to a good strain hardening capacity of 60 MPa. At 1073 K, the highest fracture elongation of ∼270% was displayed at a strain rate of 10−3 s−1. The strain rate sensitivity was estimated to be about 0.32, which is typical of alloys that show this quasi-superplastic elongation. The activation energy was also estimated to be ∼421 kJ/mol. With deformation at 1073 K at a strain rate of 10−3 s−1, the duplex microstructure transformed into a refined triplex fcc-L21-σ equiaxed microstructure. The development of the triplex equiaxed microstructure resulted from dynamic recrystallization (DRX), which assisted in the maximum superplastic-like elongation of 270%. The inability of the alloy to access true superplasticity was attributed to immense cavitation due to the high amount of the brittle σ phase, which served as de-cohesion sites for the early fracture of the sample. However, the observed quasi-superplasticity could still be useful in superplastic forming operations.

The ten articles [1–10] included in this Special Issue on “Liquid Metals” do not intend to comprehensively cover this extensive field, but, rather, to highlight recent discoveries that have greatly broadened the scope of technological applications of these materials. Improvements in understanding the physics of liquid metals are, to a large extent, due to the powerful theoretical tools in the hands of scientists, either semi-empirical [1,5,6] or ab initio (molecular dynamics, see [7]). Surface tension and wetting at metal/ceramic interfaces is an everlasting field of fundamental research with important technological implications. The review of [2] is broad enough, as the work carried out at Grenoble covers almost all interesting matters in the field. Some issues of interest in geophysics and astrophysics are discussed in [3]. The recently discovered liquid–liquid transition in several metals is dealt with in [4]. The fifth contribution [5] discusses the role of icosahedral superclusters in crystallization. In [6], thermodynamic calculations are carried out to identify the regions of the ternary phase diagram of Al-Cu-Y, where the formation of amorphous alloys is most probable. Experimental data and ab initio calculations are presented in [7] to show that an optimal microstructure is obtained if Mg is added to the Al-Si melt before than the modifier AlP alloy. Shock-induced melting of metals by means of laser driven compression is discussed in [8]. With respect to recent discoveries, one of the most outstanding developments is that of gallium alloys that are liquid at room temperature [9], and that, due to the oxide layer that readily cover their surface, maintain some “stiffness”. This has opened the possibility of 3D printing with liquid metals. The last article in this Special Issue [10] describes nano-liquid metals, a suspension of liquid metal and its alloy containing nanometer-sized particles. A room-temperature nano-liquid metal and its alloys were first introduced in the area of cooling high heat flux devices, which now is a commercial reality. However, their applications are not only in chip cooling, and can also be extended to waste heat recovery, kinetic energy harvesting, thermal interface material, etc. This is mainly due to properties such as low melting point, high thermal and electrical conductivity, as well as other additional physical or chemical properties. These articles are summarized in more detail hereafter [...]

We investigate Cu-Zr liquid alloys using molecular dynamics simulation and well-accepted embedded atom method potentials over a wide range of chemical composition and temperature as model metallic glass-forming (GF) liquids. As with other types of GF materials, the dynamics of these complex liquids are characterized by "dynamic heterogeneity" in the form of transient polymeric clusters of highly mobile atoms that are composed in turn of atomic clusters exhibiting string-like cooperative motion. In accordance with the string model of relaxation, an extension of the Adam-Gibbs (AG) model, changes in the activation free energy ΔGa with temperature of both the Cu and Zr diffusion coefficients D, and the alpha structural relaxation time τα can be described to a good approximation by changes in the average string length, L. In particular, we confirm that the strings are a concrete realization of the abstract "cooperatively rearranging regions" of AG. We also find coexisting clusters of relatively "immobile" atoms that exhibit predominantly icosahedral local packing rather than the low symmetry packing of "mobile" atoms. These two distinct types of dynamic heterogeneity are then associated with different fluid structural states. Glass-forming liquids are thus analogous to polycrystalline materials where the icosahedrally packed regions correspond to crystal grains, and the strings reside in the relatively disordered grain boundary-like regions exterior to these locally well-ordered regions. A dynamic equilibrium between localized ("immobile") and wandering ("mobile") particles exists in the liquid so that the dynamic heterogeneity can be considered to be type of self-assembly process. We also characterize changes in the local atomic free volume in the course of string-like atomic motion to better understand the initiation and propagation of these fluid excitations. [ABSTRACT FROM AUTHOR]

Knowledge of the high-pressure behavior of carbon dioxide (CO2), an important planetary material found in Venus, Earth, and Mars, is vital to the study of the evolution and dynamics of the planetary interiors as well as to the fundamental understanding of the C-O bonding and interaction between the molecules. Recent studies have revealed a number of crystalline polymorphs (CO2-I to -VII) and an amorphous phase under high pressure-temperature conditions. Nevertheless, the reported phase stability field and transition pressures at room temperature are poorly defined, especially for the amorphous phase. Here we shed light on the successive pressure-induced local structural changes and the molecular-to-nonmolecular transition of CO2 at room temperature by performing an in situ study of the local electronic structure using X-ray Raman scattering, aided by first-principle exciton calculations. We show that the transition from CO2-I to CO2-III was initiated at around 7.4 GPa, and completed at about 17 GPa. The present study also shows that at ∼37 GPa, molecular CO2 starts to polymerize to an extended structure with fourfold coordinated carbon and minor CO3 and CO-like species. The observed pressure is more than 10 GPa below previously reported. The disappearance of the minority species at 63(±3) GPa suggests that a previously unknown phase transition within the nonmolecular phase of CO2 has occurred. [ABSTRACT FROM AUTHOR]

When a material is heated, generally, it dilates. Here, we find a general trend that the average distance between a center atom and atoms in the first nearest-neighbor shell contracts for several metallic melts upon heating. Using synchrotron X-ray diffraction technique and molecular dynamics simulations, we elucidate that this anomaly is caused by the redistribution of polyhedral clusters affected by temperature. In metallic melts, the high-coordinated polyhedra are inclined to evolve into low-coordinated ones with increasing temperature. As the coordination number decreases, the average atomic distance between a center atom and atoms in the first shell of polyhedral clusters is reduced. This phenomenon is a ubiquitous feature for metallic melts consisting of various- sized polyhedra. This finding sheds light on the understanding of atomic structures and thermal behavior of disordered materials and will trigger more experimental and theoretical studies of liquids, amorphous alloys, glasses, and casting temperature effect on solidification process of crystalline materials. [ABSTRACT FROM AUTHOR]

lkali-surfactant-polymer (ASP) flooding has been considered to be one of the useful tertiary oil recovery techniques. However, field tests in China have revealed that serious side effects may occur due to using alkali. Thus alkali-free SP flooding is more favorable in China. Unfortunately, surfactants effective in ASP flooding are usually ineffective in the absence of alkali and new surfactants need to be designed. In this paper N-(3-Oxapropanoxyl)dodecanamide as a pure compound and a mixture of homologues with narrow EO number distribution, synthesized by the reaction of lauroyl chloride with diglycolamine and addition of one ethylene oxide to coconut monoethanolamide respectively, are examined for their adaptability in SP flooding. It is found that, when mixed with betaines, both products can reduce Daqing crude oil/connate water interfacial tension to a magnitude of 10-10 mNm at 45 °C in a wide surfactant concentration range, 0.01-0.5 wt%, and oil displacement tests using natural cores indicates that a tertiary oil recovery of 18.6 ± 0.4% OOIP can be achieved by SP flooding with the N-(3-Oxapropanoxyl)dodecanamide as the main surfactant without adding any alkaline agent and neutral electrolyte. N-(3-Oxapropanoxyl)dodecanamide, as a nonionic surfactant without a cloud point and producible industrially from renewable materials, is an ideal surfactant for SP flooding in the absence of an alkaline agent. [ABSTRACT FROM AUTHOR]

The formation of substitutional alloys has been restricted to elements with similar atomic radii and electronegativity. Using high-pressure at 298 K, we synthesized a face-centered cubic disordered alloy of highly dissimilar elements (large Ce and small Al atoms) by compressing the Ce3Al intermetallic compound >15 GPa or the Ce3AI metallic glass >25 GPa. Synchrotron X-ray diffraction, Ce L3-edge absorption spectroscopy, and ab initio calculations revealed that the pressure-induced Kondo volume collapse and 4f electron delocalization of Ce reduced the differences between Ce and Al and brought them within the Hume-Rothery (HR) limit for substitutional alloying. The alloy re- mained after complete release of pressure, which was also accompanied by the transformation of Ce back to its ambient 4f electron localized state and reversal of the Kondo volume collapse, resulting in a non-HR alloy at ambient conditions. [ABSTRACT FROM AUTHOR]

In the present paper, the surface tensions and interfacial energies for pure metals and alloys for different structures were predicted by combining with the evaluated thermodynamic parameters in the framework of the CALPHAD (Calculation of Phase Diagrams) method. It is shown that the calculated results are in good agreement with the existing experimental data. On the basis of the predicted values of surface tension and interfacial energy, the phase stability and phase diagram with nano-size particles can be calculated by considering the Gibbs-Thomson equation. The calculated results for pure Fe indicate that the fcc phase is more stable with the decreasing of size of particles, which is in agreement with the experimental data reported, and the phase diagram with nano-size particle can be calculated. [ABSTRACT FROM AUTHOR]

A recent report on the "room temperature superplasticity" in the Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass [Y.H. Liu et al., Science315, 1385 (2007)] was ascribed to the distinctive micrometer-sized structural heterogeneity. To verify the microstructure in this alloy, transmission electron microscopy (TEM) and anomalous small-angle x-ray scattering experiments were conducted. The results show that no micrometer-sized or nanometer-sized structural heterogeneities can be found. The micrometer-sized dark and bright regions that were previously reported as the reason for the plasticity are artifacts caused by TEM specimen preparation, rather than the intrinsic structure feature of this alloy. This finding is important for further studying the unique properties of this alloy. [ABSTRACT FROM AUTHOR]

The article focuses on long-range topological order in Ce75Al25 metallic glass (MG) that corresponds to a single crystal of indefinite length. It states that structural examinations of MG confirm it is unstrained, amorphous and isotropic but will devitrify independently into a face-centered cubic crystal under 25 gigapascals hydrostatic pressure. It mentions that synchrotron x-ray and molecular dynamics simulations elucidate that crystallization is frustrated by mismatches between Cerium and Aluminum atoms, resulting in amorphization, but that pressure will induce an electronic transition in Cerium and eliminate the mismatch.

In pressure-induced reversible structural transitions, the term "reversible" refers to the recovery of the virgin structure in a material upon complete decompression. Pressure-induced amorphous-to-crystalline transitions have been claimed to be reversible, but evidence that amorphous material recovers its virgin amorphous structure upon complete depressurization has been lacking. In amorphous As2Se3 (a-As2Se3) chalcogenide, however, we report a novel reversible amorphous-to-crystalline transition that provides compelling experimental evidence that upon complete decompression, the recovered amorphous phase is structurally the same as that of the virgin (as-cast) amorphous phase. Combining the experimental results with ab initio molecular dynamics simulations, we elucidate that the amorphization is mediated by a surplus of total free energy in the high-pressure face-centered cubic phase as compared to the virgin amorphous phase and that the structural recovery to the virgin amorphous phase is a consequence of an enhancement in covalent bonding character over interlayer forces upon complete decompression. Furthermore, we observed a two-dimensional to three-dimensional network transition under compression and its reversibility upon decompression. [ABSTRACT FROM AUTHOR]