Low melting point metals such as Field's metal and gallium are increasingly used as transition phases in stiffness-tuning soft materials and devices. Nevertheless, there is a knowledge gap on the fundamental constitutive behaviors of metals with melting points below 100 degree. This letter reports the stress-strain relationships of Field's metal at various temperatures and strain rates. This metal has the lowest melting point among metals whose constitutive behaviors have been studied systematically. Experimental results indicate that Field's metal exhibits a strain-softening behavior, in oppose to the strain-hardening behaviors of most engineering metals and alloys. A modified Johnson-Cook model is devised in this letter to describe the constitutive behaviors of Field's metal. The proposed metal will facilitate the design and analysis of functional materials and structures consisting of Field's metal.
The macroscopic elastic-plastic response of a metal polycrystal is analyzed here by homogenizing the response of a representative volume element. With this purpose, the theory developed in Hill(1967)(The essential structure of constitutive laws for metal composites and polycrystals. J. Mech. Phys. Solids, 15, 79-95) is extended so that the structural changes caused by plastic deformation are taken into account. It is found that the type of evolution assigned to the slip systems of a constituent crystal influences significantly the structure of the constitutive system characterizing the overall…
Surface melting temperature is well-known significantly lower than the bulk melting point. But we find that the interior melting temperature in ultrathin nanowires is lower than that of the surface melting . The thermal stability of helical multi-walled cylindrical gold nanowires is studied using molecular dynamics simulations. The melting temperature of gold nanowires is lower than the bulk value, but higher than that of gold nanoclusters. An interesting interior melting is revealed in the gold nanowires and the thermodynamics is closely related to interior structures. The melting starts from…
We construct a simple thermodynamic model to describe the melting of a supported metal nanoparticle with a spherically curved free surface both with and without surface melting. We use the model to investigate the results of recent molecular dynamics simulations, which suggest the melting temperature of a supported metal particle is the same as that of a free spherical particle with the same surface curvature. Our model shows that this is only the case when the contact angles of the supported solid and liquid particles are similar. This is also the case for the temperature at which surface mel…
We present an analytical solution to the two-parabola Landau model, applied to melting of metal particles with sizes in the nanoscale range. The results provide an analytical understanding of the recently observed pseudo-crystalline phase of nanoscale Sn particles. Liquid skin formation as a precursor of melting is found to occur only for particles with radii, greater than an explicitly given critical radius. The size effect of the melting temperature and the latent heat has been calculated and quantitative agreement with experiments on Sn particles was found.
We consider the surface melting of metal nanowires by solving a phenomenological two-parabola Landau model and by conducting molecular dynamics simulations of nickel and aluminium nanowires. The model suggests that surface melting will precede bulk melting when the spreading parameter $Δγ$ for the melt in contact with the solid surface is positive (i.e. if the melt wets or partially wets the surface) and the wire is sufficiently thick, as is the case for planar surfaces and sufficiently large nanoparticles. Surface melting does not occur if $Δγ$ is negative. We test this model, which assumes t…
Hydrogen enhanced cracking is one of the many failure mechanisms in metals depending on the corrosive environment. In the presented work, a multiscale constitutive model has been presented for hydrogen enhanced intergranular cracking in metals. The proposed constitutive model takes into account one of the many micromechanisms, i.e. Slip based micromechanisms active in the grain interior using crystal plasticity theory while sensitized grain boundary zone has been modelled by proposing a phenomenological constitutive model motivated from cohesive zone modelling approach. Model has been assessed…
Thermodynamic equilibrium can be sometimes reached at the interaction between metal and oxide melts in high temperature welding and metallurgical processes. Calculation of equilibrium phase composition is also one of the stages (along with kinetics analysis) of building an end-to-end physical and chemical model of real processes. Developing a thermodynamic model of high temperature processes is described in many scientific sources (1-18). Thermodynamic patterns of oxidation-reduction reactions on the metal-slag melt interface are also taken into account when building phenomenological models of…
A multiscale numerical model based on nonequilibrium thermal effect for melting of metal powder bed subjected to constant heat flux is developed. The volume shrinkage due to density change is taken into account. The nonequilibrium model is discretized by an implicit finite difference method and solved numerically using an iterative tri-diagonal matrix algorithm. The evolutions of powder bed surface temperature and various interfacial locations as well as the melting temperature range during the melting process are investigated. The results show that liquid region, upper and lower parts of mush…
Group I elements - alkali metals Li, Na, K, Rb and Cs - are examples of simple metals with one s electron in the valence band. Under pressure these elements display unusually complex structural behaviour transforming from close-packed to low symmetry open structures. Unexpectedly complex form was found for melting curves of alkalis under compression with initial increasing in accordance to Lindemann criterion and further decreasing to very low melting point. To understand complex and low symmetry structures in compressed alkalis a transformation of the electron energy levels was suggested whic…
The prediction of the melting curve of metals by extrapolation to high pressures and temperatures based on the Lindemann-Gilvarry criterion (LG) assuming harmonic Debye solid is presented. The LG formulation uses the bulk modulus B and its pressure derivative B' as fit parameters deduced directly from the equation of state, however, the results are not unique and strongly depends on the chosen equation of state (EOS). By introducing a constraint that the bulk moduli parameters B and B' must simultaneously obey the Lindemann-Gilvarry criterion (LG) and the EOS, consistent bulk moduli are derive…
Thermodynamics analysis of oxidation-reduction reactions between metal melt and slag (1) provides answers to certain practical issues such as the path of specific chemical reactions, final (equilibrium) phase composition, and the elements that are reduced and oxidized at given physical parameters. Although considerable, this is obviously not enough to analyze real technological systems, because the required equilibrium cannot be normally achieved despite high temperatures of welding and metallurgical processes. Hence, a dynamic problem has to be resolved here, which is calculating phase compos…
We have demonstrated a new method for the large-area graphene growth, which can lead to a scalable low-cost high-throughput production technology. The method is based on growing single-layer or few-layer graphene films from a molten phase. The process involves dissolving carbon inside a molten metal at a specified temperature and then allowing the dissolved carbon to nucleate and grow on top of the melt at a lower temperature. The examined metals for the metal - carbon melts included copper and nickel. For the latter, pristine single layer graphene was grown successfully. The resulting graphen…
We demonstrate that the melting points and other thermodynamic quantities of the alkali metals can be calculated based on static crystalline properties. To do this we derive analytic interatomic potentials for the alkali metals fitted precisely to cohesive and vacancy energies, elastic moduli, lattice parameter and crystal stability. These potentials are then used to calculate melting points by simulating the equilibration of solid and liquid samples in thermal contact at ambient pressure. With the exception of lithium, remarkably good agreement is found with experimental values. The instabili…
Ductile metals undergo a considerable amount of plastic deformation before failure. Void nucleation, growth and coalescence is the mechanism of failure in such metals. α/β titanium alloys are ductile in nature and are widely used for their unique set of properties like specific strength, fracture toughness, corrosion resistance and resistance to fatigue failures. Voids in these alloys were reported to nucleate on the phase boundaries between α and β phase. Based on the findings of crystal plasticity finite element method (CPFEM) based investigation of the void growth at the interface of α and …
Observations are reported in isothermal torsional oscillation tests on melts of isotactic polypropylene (iPP) and low-density polyethylene (LDPE) in the intervals of temperature between 190 and 250C (iPP) and between 120 and 190C (LDPE). With reference to the concept of transient networks, constitutive equations are developed for the viscoelastic response of polymer melts at three-dimensional deformations with small strains. A melt is treated as an equivalent network of strands bridged by temporary junctions (entanglements and physical cross-links whose life-times exceed the characteristic tim…
We present molecular dynamics simulations of the homogeneous (mechanical) melting transition of a bcc metal, vanadium. We study both the nominally perfect crystal as well as one that includes point defects. According to the Born criterion, a solid cannot be expanded above a critical volume, at which a 'rigidity catastrophe' occurs. This catastrophe is caused by the vanishing of the elastic shear modulus. We found that this critical volume is independent of the route by which it is reached whether by heating the crystal, or by adding interstitials at a constant temperature which expand the latt…
Finding an accurate stress-strain relation, able to describe the mechanical behavior of metals during {forming} and machining processes, is an important challenge in several fields of mechanics, with significant repercussions in the technological field. Indeed, in order to predict the real mechanical behavior of materials, constitutive laws must be able to take into account elastic, viscous and plastic phenomena. Most constitutive models are based on empirical evidence and/or theoretical approaches, and provide a good prediction of the mechanical behavior of several materials. Here we present …
We present molecular dynamics simulations of the thermodynamic melting transition of a bcc metal, vanadium using the Finnis-Sinclair potential. We studied the structural, transport and energetic properties of slabs made of 27 atomic layers with a free surface. We investigated premelting phenomena at the low-index surfaces of vanadium; V(111), V(001), and V(011), finding that as the temperature increases, the V(111) surface disorders first, then the V(100) surface, while the V(110) surface remains stable up to the melting temperature. Also, as the temperature increases, the disorder spreads fro…
The p-V-T equation of state of magnesium metal has been measured up to 20 GPa and 1500 K using both multianvil and opposite anvil techniques combined with synchrotron X-ray diffraction. To fit the experimental data, the model of Anderson-Grüneisen has been used with fixed parameter δT. The 300-K bulk modulus of B0 = 32.5(1) GPa and its first pressure derivative, B0' = 3.73(2), have been obtained by fitting available data up to 20 GPa to Murnaghan equation of state. Thermal expansion at ambient pressure has been described using second order polynomial with coefficients a = 25(2)x10-6 K-1 and b …
The dependencies of the melting point and the lattice parameter of supported metal nanoclusters as functions of clusters height are theoretically investigated in the framework of the uniform approach. The vacancy mechanism describing the melting point and the lattice parameter shifts in nanoclusters with decrease of their size is proposed. It is shown that under the high vacuum conditions (p<10^-7 torr) the essential role in clusters melting point and lattice parameter shifts is played by the van der Waals forces of cluster-substrate interation. The proposed model satisfactorily accounts for t…
The high-pressure melting curves of metals provide simple and useful tests for theories of melting, as well as important constraints for the modeling of planetary interiors. Here, we present an experimental technique that reveals the latent heat of fusion of a metal sample compressed inside a diamond anvil cell. The technique combines microsecond-timescale pulsed electrical heating with an internally-heated diamond anvil cell for the first time. Further, we use the technique to measure the melting curve of platinum to the highest pressure measured to date. Melting temperature increases from $\…
Hybrid glasses connect emerging fields of metal-organic frameworks (MOFs) with the glass-formation, amorphization, and melting processes of these structurally diverse and chemically versatile systems. Most zeolites, including MOFs, amorphize around the glass transition, devitrifying and then melting at much higher temperatures. The relationship between the two processes has so far not been investigated. Herein we show how heating first results in a low density perfect glass, following an order-order transition, leading to a super-strong liquid of low fragility that dynamically controls MOF col…
Characterizing meltpool shape and geometry is essential in metal Additive Manufacturing (MAM) to control the printing process and avoid defects. Predicting meltpool flaws based on process parameters and powder material is difficult due to the complex nature of MAM process. Machine learning (ML) techniques can be useful in connecting process parameters to the type of flaws in the meltpool. In this work, we introduced a comprehensive framework for benchmarking ML for melt pool characterization. An extensive experimental dataset has been collected from more than 80 MAM articles containing MAM pro…
It is claimed that all of the pressure scales of the reported melting curves derived by diamond anvil cell experiments require a correction which takes into account the pressure thermal shift, where vanadium is an illustrative example. The linear behavior of the thermal pressure (Pth) vs. the temperature, as predicted by first principles theoretical assumptions is then experimentally confirmed. This allows extrapolation to determine of the actual pressure and thermal temperature at the melt. Accounting for the role of the pressure transmitting media in diamond anvil cell experiments, the analy…
We present calculations of the free energy, and hence the melting properties, of a simple tight-binding model for transition metals in the region of d-band filling near the middle of a d-series, the parameters of the model being designed to mimic molybdenum. The melting properties are calculated for pressures ranging from ambient to several Mbar. The model is intended to be the simplest possible tight-binding representation of the two basic parts of the energy: first, the pairwise repulsion due to Fermi exclusion; and second, the d-band bonding energy described in terms of an electronic densit…
A solution for the most important problems in 3D printing technology (long print times, small build volumes and limited material properties) is proposed. Method is based on the fact that temperature of melts crystallization can be shifted up by pressure. Required pressure can be created by Ampere force caused by electric current in the melt flow. Magnetohydrodynamical model (with heat taken into account) is developed. It has been shown that additional heating of melt by this current can be overcome by appropriate choice of tunable parameters and introduction of some additional magnetic field. …
We propose a modification of the embedded-atom method-type potential aiming at reconciling simulated melting and ground-state properties of metals by means of classical molecular dynamics. Considering titanium, magnesium, gold, and platinum as case studies, we demonstrate that simulations performed with the modified force field yield quantitatively correctly both the melting temperature of the metals and their ground-state properties. It is shown that the accounting for the long-range interatomic interactions noticeably affect the melting point assessment. The introduced modification weakens t…
We present an extensive but concise review of our present understanding, largely based on theory and simulation work from our group, on the equilibrium behavior of solid surfaces and nanosystems close to the bulk melting point. In the first part we define phenomena, in particular surface melting and nonmelting, and review some related theoretical approaches, from heuristic theories to computer simulation. In the second part we describe the surface melting/nonmelting behavior of several different classes of solids, ranging from van der Waals crystals, to valence semiconductors, to ionic crystal…
It is generally assumed that solid hydrogen will transform into a metallic alkali-like crystal at sufficiently high pressure. However, some theoretical models have also suggested that compressed hydrogen may form an unusual two-component (protons and electrons) metallic fluid at low temperature, or possibly even a zero-temperature liquid ground state. The existence of these new states of matter is conditional on the presence of a maximum in the melting temperature versus pressure curve (the 'melt line'). Previous measurements of the hydrogen melt line up to pressures of 44 GPa have led to cont…
A crystal of pure nickel grows from its melt at a rate that reaches 70 meters per second. This extraordinary growth rate has led to the suggestion that metallic crystals might provide the next generation of phase change materials. The huge crystal growth rates of metals are a consequence of kinetics without activated control, in sharp contrast to the prediction of the classic theory of crystal growth. While the existence of growth kinetics without barriers is now well established in atomic melts, no physical explanation for the absence of an activation barrier to ordering has been established.…
We report the measurements of the thermal conductivity ($κ$) of iron (Fe) and nickel (Ni) at high pressures and high temperatures. $κ$ values are estimated from the temperature measurements across the sample surface in a laser heated diamond anvil cell (LHDAC) and using the COMSOL software. Near-isothermal $κ$'s are observed to increase with pressure in both the metals due to the increase of density of the pressed metals. In both metals $κ$'s are observed to follow a sharp fall during melting at different pressure points and are consistence with the other multi-anvil measurements. Constant val…
A microscopic picture of the ``preparation'' of a crystal to the transition to liquid state at the approach to melting temperature is proposed. Basing on simple crystallogeometric considerations and the analysis of the computational results for corresponding anharmonic characteristics an evaluation is given for the magnitude of atomic displacements leading to the appearance of close packed Bernal pseudonuclei in the solid phase. A physical meaning of the classical Lindeman criterion and the mechanisms of the formation of free volume in the crystal phase are discussed.
The paper presents the results of molecular dynamics study of the viscosity of nickel-containing binary metal melts for a wide range of temperatures, including the region of the equilibrium liquid phase and supercooled melt. It is shown that the temperature dependencies of the viscosity of binary metal melts are described by the Kelton's quasi-universal model. Based on the analysis of the viscosity coefficient of the binary melt composition within the framework of the Rosenfeld's scale transfor\-mations, it has been established that to correctly describe the viscosity of binary/multi\-componen…
A Universal Polybromide Melt Strategy for the Direct Conversion of Metals into Optoelectronic-Grade Bromide Perovskites
Ben Gurion University of the Negev（本-古里安大学）；Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev（本-古里安大学伊尔斯·卡茨纳米科学与技术研究所）
We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding is supplanted by amorphization in a highly localized nanoscale band, which allows massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are, lack of dislocation slip systems, low thermal conduction and temperature near the melting point. The first two are ex…
A simple method for detection of melting event in laser-heated diamond anvil cells (DACs) is introduced. The melting is registered optically by the formation of spherical drops of the investigated material as heated in an inert pressure transmitting medium. Feasibility of the method is demonstrated on the examples of metal (iron and gold) and iron oxide (Fe2O3), materials molten at pressures over 40 GPa employing a portable laser heating system.
Large scale molecular dynamics (MD) simulations are performed to study and to model the ejecta production from the dynamic fragmentation of shock-loaded metals under melt conditions. A generic 3D crystal in contact with vacuum containing about 10^8 atoms and with a sinusoidal free surface roughness is shock loaded so as to undergo a solid-liquid phase change on shock. The reflection of the shock wave at the interface metal/vacuum gives rise to the ejection of 2D jets/sheets of atoms (Richtmyer-Meshkov instabilities in the continuum limit) which develop and break up, forming ejecta (fragments) …
In this paper we present a thermodynamically consistent material model which is capable of modelling ductile-to brittle failure mode transition in ductile material undergoing deformations at high strain rates, and demonstrate the performance of the model in a numerical study using a fully coupled thermal-structural finite element analysis of a notched aluminium alloy specimen loaded in cyclic tension. The model is based on an objective representation of the deformation and stress measures and on a rate type constitutive equations. It does not only complies with the principles of material model…
Phonon collapse and anharmonic melting of the 3D charge-density wave in kagome metals
Donostia International Physics Center (DIPC)（圣塞巴斯蒂安国际物理中心）；University of the Basque Country (UPV/EHU)（巴斯克大学）；Centro de Física de Materiales (CSIC-UPV/EHU)（材料物理中心）；Max Planck Institute for the Structure and Dynamics of Matter（马普物质结构与动力学研究所）；Max Planck Institute for Chemical Physics of Solids（马普固体化学物理研究所）
The relaxation dynamics of glass-forming systems shows a multitude of features that are absent in normal liquids, such as non-exponential relaxation and a strong temperature-dependence of the relaxation time. Connecting these dynamic properties to the microscopic structure of the system is very challenging because of the presence of the structural disorder. Here we use computer simulations of a metallic glass-former to establish such a connection. By probing the temperature and wave-vector dependence of the intermediate scattering function we find that the relaxation dynamics of the glassy mel…
Understanding melting in metals is a hot topic of present research. This may be accomplished by pumping the system with infrared (IR) laser radiation, and probing it with hard X-rays produced by an X-ray Free-Electron Laser (XFEL). In this work we studied nanostructured polycrystalline thin films of platinum that were illuminated by IR radiation of increasing fluences. We characterized the structural response as well as the nucleation and propagation of the liquid phase as a function of time delay between the IR pump and X-ray probe. We observed partial melting of the samples for IR fluences h…
Gradient structured (GS) metals processed by severe plastic deformation techniques can be designed to achieve simultaneously high strength and high ductility. Significant kinematic hardening is key to their excellent strain hardening capacity which results in a favorable strength-ductility combination. Unfortunately, no constitutive model has been established to simulate and analyze the characteristic kinematic hardening behavior of GS metal to understand the relationship between their microstructure and macroscopic response. In this work, we developed a deformation-mechanismbased strain gradi…
Zr-based AB2-Laves phase type alloys containing the same type of A and B metals, have been prepared from pure elements by melting and subsequent re-melting under argon atmosphere by using a HF-induction levitation furnace. Characterization of the alloys has resulted from powder X-Ray Diffraction (XRD) measurements and SEM/EDX analyses. Systematic PCI (Pressure-Composition-Isotherms) measurements have been recorded at 20 and 90 oC, using a high-pressure Sievert's type apparatus. The purpose of this study is to find a series of alloys promptly forming metal hydrides (MH) with suitable properties…
Molecular dynamics simulations have been used to study the mechanism of ion beam mixing in metal bilayers. We are able to explain the ion induced low-temperature phase stability and melting behavior of bilayers using only a simple ballistic picture up to 10 keV ion energies. The atomic mass ratio of the overlayer and the substrate constituents seems to be a key quantity in understanding atomic mixing. The critical bilayer mass ratio of $δ< 0.33$ is required for the occurrence of a thermal spike (local melting) with a lifetime of $τ> 0.3$ ps at low-energy ion irradiation (1 keV) due to a ballis…
The ratio of the mean square amplitude root of thermal vibrations and the interatomic distance is a universal constant dls at the melting temperature Tm. The classical Gibbs free energy change completed by a volume energy saving els (or Delg)*DHm that governs the liquid to solid and liquid to ultra-stable glass transformations leads to a universal constant equal to els (or Delg), DHm being the crystal melting enthalpy. The minimum values 0.217 of els and 0.103 of dls are used to predict ultra-stable glass formation in pure metallic liquid elements at a universal reduced temperature 0g = (Tg-Tm…
In this paper, the Wulff cluster model combined phonon calculation is used to investigate the relationship between the structure of metallic melts (Pb/Al) and the abnormal viscosity change. Although absolute value of the surface energy does not change significantly with temperature, the Wulff shape changed evidently. When temperature raise to 975K, Pb(321) surface that has the highest interaction strength completely disappears, while the abnormal viscosity drop happens at the same temperature range. Oppositely, Al(100) surface that has the lowest interaction strength disappears when temperatur…
Conventional 3D printings are generally time-consuming and printable metal inks are rather limited. From an alternative way, we proposed a liquid phase 3D printing for quickly making metal objects. Through introducing metal alloys whose melting point is slightly above room temperature as printing inks, several representative structures spanning from one, two and three dimension to more complex patterns were demonstrated to be quickly fabricated. Compared with the air cooling in a conventional 3D printing, the liquid-phase-manufacturing offers a much higher cooling rate and thus significantly i…
The electronic phase diagram of the weak spin-orbit Mott insulator (Sr(1-x)Lax)3Ir2O7 is determined via an exhaustive experimental study. Upon doping electrons via La substitution, an immediate collapse in resistivity occurs along with a narrow regime of nanoscale phase separation comprised of antiferromagnetic, insulating regions and paramagnetic, metallic puddles persisting until x~0.04. Continued electron doping results in an abrupt, first-order phase boundary where the Neel state is suppressed and a homogenous, correlated, metallic state appears with an enhanced spin susceptibility and loc…
Charge density waves (CDWs) are symmetry-broken ground states that commonly occur in low-dimensional metals due to strong electron-electron and/or electron-phonon coupling. The non-equilibrium carrier distribution established via photodoping with femtosecond laser pulses readily quenches these ground states and induces an ultrafast insulator-to-metal phase transition. To date, CDW melting has been mainly investigated in the single-photon and tunneling regimes, while the intermediate multi-photon regime has received little attention. Here we excite one-dimensional indium wires with a CDW gap of…
Microcanonical molecular dynamics study of the spontaneous alloying(SA), which is a manifestation of fast atomic diffusion in a nano-sized metal cluster, is done in terms of a simple two dimensional binary Morse model. Important features observed by Yasuda and Mori are well reproduced in our simulation. The temperature dependence and size dependence of the SA phenomena are extensively explored by examining long time dynamics. The dominant role of negative heat of solution in completing the SA is also discussed. We point out that a presence of melting surface induces the diffusion of core atoms…
We determine the structure and melting behavior of supported metallic clusters using an ab initio density-functional-based treatment of intracluster interactions and an approximate treatment of the surface as an idealized smooth plane yielding an effective Lennard-Jones interaction with the ions of the cluster. We apply this model to determine the structure of sodium clusters containing from 4 to 22 atoms, treating the cluster-surface interaction strength as a variable parameter. For a strong cluster-surface interaction, the clusters form two-dimensional (2D) monolayer structures; comparisons …
One of the challenges for development, qualification and optimisation of arc welding processes lies in characterising the complex melt-pool behaviour which exhibits highly non-linear responses to variations of process parameters. The present work presents a simulation-based approach to describe the melt-pool behaviour in root-pass gas metal arc welding (GMAW). Three-dimensional numerical simulations have been performed using an enhanced physics-based computational model to unravel the effect of groove shape on complex unsteady heat and fluid flow in GMAW. The influence of surface deformations …
