Solidification Of Liquid Metal Research Articles

Liquid Metal Flow Under Traveling Magnetic Field—Solidification Simulation and Pulsating Flow Analysis

Non steady applied magnetic field impact on a liquid metal has good prospects for industry. For a better understanding of heat and mass transfer processes under these circumstances, numerical simulations are needed. A combination of finite elements and volumes methods was used to calculate the flow and solidification of liquid metal under electromagnetic influence. Validation of numerical results was carried out by means of measuring with ultrasound Doppler velocimetry technique, as well as with neutron radiography snapshots of the position and shape of the solid/liquid interface. As a result of the first part of the work, a numerical model of electromagnetic stirring and solidification was developed and validated. This model could be an effective tool for analyzing the electromagnetic stirring during the solidification process. In the second part, the dependences of the velocity pulsation amplitude and the melt velocity maximum value on the magnetic field pulsation frequency are obtained. The ability of the pulsating force to develop higher values of the liquid metal velocity at a frequency close to the MHD resonance was found numerically. The obtained characteristics give a more detailed description of the electrically conductive liquid behaviour under action of pulsating traveling magnetic field.

Visualization of phase distribution in lead–bismuth eutectic during one-dimensional solidification process

Solidification process of lead–bismuth eutectic (LBE) is one of the key phenomena to prevent flow channel blockage accident in an LBE-cooled accelerator-driven system. However, the solidification of liquid metal cannot be observed optically and it is difficult to detect noninvasively. In this study, the one-dimensional solidification process of the LBE was visualized by pulsed neutron transmission imaging. Neutrons have higher transmittivity to the LBE than X-ray and neutron transmission spectrum of the LBE sample can be obtained by pulsed neutron imaging technique. The solid and liquid phases of the LBE were identified during the solidification process by the presence or absence of Bragg edge in the measured neutron transmission spectrum, and the transient behavior of the solid–liquid interface could be visualized. In addition, the characteristic spatial distribution of the crystalline structure was found in Bragg-edge transmission image after the solidification.

Solid-liquid metal interface definition studies using capillary fluctuation method

We present a review of various commonly used numerical approaches used to define the interface of a crystal-melt structure at the atomic scale using order parameters, local positioning and density functions. The effectiveness and deviations in interfacial stiffness, as calculated through the capillary fluctuation method, are compared between two methods, centrosymmetry parameter and the local concentration parameter, for the face-centered cubic structure of aluminum. In addition, a new maximum difference filtering technique is introduced that uses existing order parameters to create finely detailed interfaces between two phases. The filtering technique is used to define various fractal scales at the interface, and to demonstrate the effect on interfacial stiffness due to the change in scale on the fluctuation analysis for a range of wavenumbers. The presented material is intended for applications of the capillary fluctuation method where the consistent and automatic definition of two-phase interfaces is required for a large number of atom coordinate configurations.

Monitoring of Welding Process Parameters in Gas Tungsten Arc Welding of Carbon Steel Weldments

Results of present study show the possibilities to monitor and control the automatic gas tungsten arc welding process using additional filler rod, and investigate the evolution of microstructure and the mechanical characteristics of carbon steel weldments joint under the different welding parameters: welding current, arc voltage, and travel speed. Three types of weldments were produced and tested: build-up welds, U-grooved samples, and butt welds. Penetration and depth of heat affected zone in all types of welds are influenced especially by the welding current. Dendrite structure formed after welding gives a good indication of the thermodynamic processes during liquid metal solidification, welds are free from defects. The welded joints showed that crystal orientation and shape in the weld zone depend on thermodynamic processes during solidification and welding mode. The frequency and size of the successive droplets of the molten metal from the filler rod has been registered by piezoelectric sensor and due to the collected data the welding parameters and herewith the geometry and structure of heat affected zone and weld bead have been controlled. DOI: http://dx.doi.org/10.5755/j01.mech.25.1.22158

ЗАСТОСУВАННЯ РОЗРЯДНИКІВ НАПРУЖЕНЬ В ОСНОВНИХ ВУЗЛАХ ТЕХНОЛОГІЧНОГО УСТАТКУВАННЯ МБЛЗ

Presence of cracks and other surface defects is completely prohibited at exploitation of industrial facilities. This condition is of vital importance for component parts of a complex of big equipment. For example, for continuous casting machines (CCMs), whose total weight exceeds several thousand metric tons a failure of a single component part can lead to serious consequences, due to imminent hue material losses. Such hard conditions of such equipment not only influence its operation, reducing its service life, but also may have a negative impact on the quality of production. Such negative influence can be expressed in the following way: regulation of the main units may be altered following overheating of the equipment, due to thermal expansion of mostly heated elements. In case of presence of cracks in the most loaded unit of dummy bar –its head part its bearing capacity may be altered and appearance of excessive deformations may not be excluded, i.e. its transverse dimensions may be changed. Besides, cracks in the locking part of the dummy bar are out of the question, in order to avoid solidification of liquid metal in cracks.The problem of reducing intensity of cracks formation can be solved in different ways. Its practical solution depends upon the part’s design and peculiarities of its loading. For operation of dummy bars of slab casting CCMs it should be noted that this problem is closely connected with asymmetric design of dummy bars heads and one-way heat delivery and removal for its locking part. The finite elements method was used for the analysis of stress-strain state in the article. Three-dimensional simulation models were divided into finite elements and after that they underwent various theoretically possible loads. Simulation made it possible to establish the most vulnerable sections of the design, undergoing most severe loads, in case they are applied. Particularly, it was found out that the edge parts of transverse section of a dummy bar head experience the biggest deformations, consequently, cracks can spring up at a certain pitch and develop on the surface of the projection of the lock. The analysis of the initial data showed that for reduction of thermal strain in the lock projection it was necessary to make deformation inside its upper layers more free. It will be is possible if a transverse slot is made, dividing the projection length into two elements. Heating and cooling of the surface lock’s layer could become safer, at that, from the point of view of elongating stresses, thus reducing the probability of cracks formation.

Evolution of local atomic structures during rapid solidification of liquid metal W

Molecular dynamics (MD) simulations were performed to investigate the evolution of local atomic structure during rapid solidification of liquid metal W. The microstructures were characterized by means of potential energy (PE) per atom, pair distribution function and largest standard cluster analysis (LSCA). Instead of [12/555] perfect icosahedra, the [8/555 2/544 2/433] distorted icosahedra dominated in W monatomic metallic glasses (MGs). With the decrease of temperature, these clusters in metal W systems aggregated steeply into icosahedral medium-range orders (IMROs), especially in the super-cooling liquid region. Moreover, the maximal size [Formula: see text] of IMROs played a control role in the formation of W monatomic MGs rather than the number [Formula: see text]. The mean local fivefold symmetry [Formula: see text] of IMROs was demonstrated to be an effective indicator to characterize the glass transition of monatomic metal W liquids.

Phase formation under non-equilibrium processing conditions: rapid solidification processing and mechanical alloying

Rapid solidification processing (RSP) of metallic alloys, involving solidification of liquid metals at very high rates, results in the formation of a variety of metastable phases such as supersaturated solid solutions, crystalline intermetallic compounds, quasicrystalline phases, and metallic glasses. Additionally, significant refinement of the grain sizes and segregation patterns also occurs. Mechanical alloying (MA), another powerful non-equilibrium processing technique, utilizes repeated cold welding, fracturing, and rewelding of powder particles in a high-energy ball mill. MA also results in the formation of metastable phases and microstructural refinement similar to what happens during RSP. Consequently, comparisons are frequently made between the phases produced by RSP and MA and the general understanding is that they both result in similar metastable effects. A detailed analysis of the metastable phases produced by RSP and MA is made in the present work, and it is shown that even though the effects may appear similar, the mechanisms of formation and the composition ranges in which particular phases form are quite different. These two methods also have some unique features and produce different phases. The differences have been ascribed to the fact that RSP involves solidification from the melt while MA is a completely solid-state process that is not restricted by the phase diagram.

High P–T experiments and first principles calculations of the diffusion of Si and Cr in liquid iron

Chemical diffusion rates of Si and Cr in liquid iron have been measured over the P–T range of 1–18GPa and 1873–2428K. The experiments were performed using a multi-anvil apparatus with diffusion couples comprised of pure iron and iron alloy placed end to end in a vertical orientation. In order to extend our dataset to the Earth’s core–mantle boundary and to compare experimental data with theoretical diffusion rates calculated under laboratory-accessible conditions, we have also performed first principles molecular dynamic simulations (FP-MD) and calculated self-diffusion coefficients and activation parameters for Si, Cr, and Fe diffusion in liquid Fe, Fe0.92Si0.08 and Fe0.92Cr0.08 compositions over the P–T range of 1bar–135GPa and 2200–5500K. Over the entire range of pressures and temperatures studied using both methods, diffusion coefficients are described well using an exponential function of the homologous temperature relation, D=Dhexp(−gTh), where Th=Tm/T, Tm is the melting temperature at the pressure of interest and g and Dh are constants. Our findings indicate constant diffusivities of approximately 4×10−9m2s−1 for Si and Cr and 5×10−9m2s−1 for Fe along the melting curve from ambient to core pressures in all liquid compositions studied, with an increase of ∼0.8logunits at T=2Tm. Differences between experimental data and computational results are less than 0.1logunits. Structural properties of liquid iron alloys analyzed using partial radial distribution functions (RDFs) show the average distance between two Fe atoms, rFe–Fe, is identical to that of rFe–Si and rFe–Cr over the entire P–T range of study, which supports that the diffusion of Si and Cr (and thus likely other species of similar atomic radii) occurs via direct substitution with Fe. Diffusion coefficients and interatomic distances used to calculate liquid viscosities via the Stokes–Einstein relation yield constant viscosity along the melting curve of ∼6mPas for liquid Fe, ∼7mPas for liquid Fe0.92Cr0.08, and ∼8mPas for liquid Fe0.92Si0.08, with a decrease of ∼0.8logunits at T=2Tm. The data can also be reproduced within <10% using the Arrhenian model with derivatives of the activation parameters determined over a very wide range of P–T conditions. Verification of a homologous temperature dependence of diffusion in liquid metals, as well as the excellent agreement between experimental results and FP-MD simulations, provides a new and simple framework for interpreting and modeling mass transport processes of liquid iron alloys in all planetary bodies regardless of size. Our results are used to evaluate the kinetics of metal–silicate chemical equilibration during core formation and diffusivity contrasts across a solid–liquid metal interface, i.e. at the inner core boundary.

THE EFFECTS OF DISSOLUTION OF THE SOLID NICKEL IN LIQUID ALUMINIUM

The preparation of a large number of materials trough the propagating exothermic reactions has been the objective of numerous investigation. Self-propagating reactions are typically associated with high temperatures and extremely steep thermal gradients and thus offer the opportunity to investigate the formation of intermediate and metastable phases. Such reactions are also of interest from a practical point of view since, as has been described in numerous literature accounts, they provide the opportunity to prepare materials with unique properties.In this study the thermal effects of dissolution on the solid nickel in liquid aluminium and formation intermetallic phases was studied by simple experimental procedure. The thermal effects generated by exothermic solid-liquid metal interaction was judged by the rise of temperature in the system. Depending on experimental conditions, two different regimes of behavior were found: solid-liquid interaction leading to the considerable rise of the temperature in the system, and characterized by continuos decrease of the temperature in the system with time. The results of the experiments on the heat effects during the interaction of solid nickel with different particle size and liquid aluminium, with and without external mixing, are presented. It has been shown that, depending on experimental conditions, the evolved heat may influence the structure of a zone near to the solid-liquid interface. The experimental procedure correlates with the practical conditions of semi-industrial production of aluminium-nickel master alloys with relatively high percentage of nickel.

Laser Deep Penetration Welding of an Aluminum Alloy with Simultaneously Applied Vibrations

In aluminum welding, the grain structure of produced seams is an essential factor with respect to the seam properties. In the casting technology the effect of mechanical vibrations on the grain growth during the solidification of liquid metals is known as a refinement method. In this paper, the transferability of this approach from comparatively long-time processes in the field of casting to the short-time process of laser deep penetration welding is investigated. Therefore, specimens were sinusoidal vibrated with frequencies up to 4 kHz during bead-on-plate full-penetration welding experiments. The resulting grain size was determined by applying the circular intercept procedure on the center of a cross-section micrograph of each weld. The results show that grain refinement is in general achievable by mechanical vibrations in the audible frequency range during laser full penetration keyhole welding of the aluminum alloy EN AW-5083.

Process-Structure-Property Relationships for 316L Stainless Steel Fabricated by Additive Manufacturing and Its Implication for Component Engineering

We investigate the process-structure-property relationships for 316L stainless steel prototyping utilizing 3-D laser engineered net shaping (LENS), a commercial direct energy deposition additive manufacturing process. The study concluded that the resultant physical metallurgy of 3-D LENS 316L prototypes is dictated by the interactive metallurgical reactions, during instantaneous powder feeding/melting, molten metal flow and liquid metal solidification. The study also showed 3-D LENS manufacturing is capable of building high strength and ductile 316L prototypes due to its fine cellular spacing from fast solidification cooling, and the well-fused epitaxial interfaces at metal flow trails and interpass boundaries. However, without further LENS process control and optimization, the deposits are vulnerable to localized hardness variation attributed to heterogeneous microstructure, i.e., the interpass heat-affected zone (HAZ) from repetitive thermal heating during successive layer depositions. Most significantly, the current deposits exhibit anisotropic tensile behavior, i.e., lower strain and/or premature interpass delamination parallel to build direction (axial). This anisotropic behavior is attributed to the presence of interpass HAZ, which coexists with flying feedstock inclusions and porosity from incomplete molten metal fusion. The current observations and findings contribute to the scientific basis for future process control and optimization necessary for material property control and defect mitigation.

Numerical investigation on the fluid flow and heat transfer in electroslag remelting furnace with triple-electrode

Electroslag remelting (ESR) furnace with triple-electrode is always used to produce large ingots and the process complexity makes the application not widely spread. Thus, a transient three-dimensional coupled model in industrial scale has been developed to investigate the coupled magneto-hydrodynamics two-phase flow and heat transfer in system. Different from the previous studies with multi-electrode, the current work reveals the triple-electrode ESR with the formation of metal droplets and the solidification of liquid metal. Compared with single-electrode system with the same fill ratio, the heat source in the slag pool with triple-electrode is much more dispersive, and the U-shape metal pool in the ESR furnace with triple-electrode is much shallower and flatter than the V-shaped one in the single-electrode system. A shorter distance from each electrode to the center of system brings a higher heat efficiency, as well as a deeper and narrower metal pool.

Microstructure, fracture toughness and compressive property of as-cast and directionally solidified NiAl-based eutectic composite

Microstructure and room temperature mechanical property of as-cast and directionally solidified NiAl-Cr(Mo) eutectic composite were investigated by SEM, EDS, three point bending test and compression test. The microstructure of as-cast alloy consists of Cr(Mo) primary dendrites and equiaxed eutectic cells. For the directional solidification of liquid metal cooling technique (LMC), only the small quantity of Cr(Mo) primary dendrites appear in the beginning of solidification, and the fully and well-aligned lamellar structure parallel to the growth direction is obtained in the steady-state zone. However, the Cr(Mo) primary phase is always observed in the whole directional solidification of zone melted liquid metal cooling technique (ZMLMC), and the eutectic lamellas are disordered and not parallel to the growth direction in the steady-state zone. Compared to the ZMLMC alloys, the LMC alloy has the better room temperature fracture toughness and compressive property due to the well-aligned lamellar structure. Crack propagation and fracture surface are also observed to understand the fracture behavior.

Numerical Simulation of Electroslag Remelting Process of Hollow Ingot with T-shape Current Supplying Mold

A three dimensional quasi-steady state mathematical model of the slag bath and hollowingot has been established based on the newly developed electroslag remelting( ESR) technology for hollowingot manufacture. The electromagnetic, flowand temperature fields during the electroslag remelting hollowingot process with and without the current supplying mold( CSM)have been simulated using commercial software ANSYS. Computational results showed that the maximum current density and joule heat of the slag bath were obtained in the conductive section of T-shaped CSM,where the fluid flowvelocity was much faster and the temperature field of the slag bath was more uniform,and the metal pool shape was shallower. The CSMcan keep slag bath and metal pool temperature constantly during the exchange of electrodes,which avoided the rapid solidification of liquid metal near the mold wall to generated slag ditchs when the slag bath temperature drops rapidly. The solidification quality and surface quality of hollowingots were thus greatly improved.

Flow, heat and mass transfers during solidification under traveling/rotating magnetic field

In this paper, we present the relative problem of heat and mass transfer to adopt a means of imposing an electromagnetic field to improve solutal segregation (macrosegregation) during liquid metal solidification. A well-validated, quasi-two-dimensional solidifying experi- mental benchmark was introduced, which allowed us to observe the temperature field evolution and to provide the evident clues of phase transformation. We also observed naturally formed solutal segregations in the post-mortem sample. The idea of imposing a modulated magnetic field while optimizing modulation frequency and having a cable to suppress solutal segregation was confirmed by multi- scale numerical modeling. Magnetohydrodynamics, flow driven by a modulated traveling magnetic field, was experimentally studied. Furthermore, a more practical cylindrical shape of liquid metal bulk driven by a perma- nent helical magnetic field has been achieved. The spatial flow behaviors suggested an appropriate magnetic field with optimized electromagnetic parameters for obtaining high-quality, low-defect casting products.

Accelerating solidification process simulation for large-sized system of liquid metal atoms using GPU with CUDA

Molecular dynamics simulation is a powerful tool to simulate and analyze complex physical processes and phenomena at atomic characteristic for predicting the natural time-evolution of a system of atoms. Precise simulation of physical processes has strong requirements both in the simulation size and computing timescale. Therefore, finding available computing resources is crucial to accelerate computation. However, a tremendous computational resource (GPGPU) are recently being utilized for general purpose computing due to its high performance of floating-point arithmetic operation, wide memory bandwidth and enhanced programmability. As for the most time-consuming component in MD simulation calculation during the case of studying liquid metal solidification processes, this paper presents a fine-grained spatial decomposition method to accelerate the computation of update of neighbor lists and interaction force calculation by take advantage of modern graphics processors units (GPU), enlarging the scale of the simulation system to a simulation system involving 10 000 000 atoms. In addition, a number of evaluations and tests, ranging from executions on different precision enabled-CUDA versions, over various types of GPU (NVIDIA 480GTX, 580GTX and M2050) to CPU clusters with different number of CPU cores are discussed. The experimental results demonstrate that GPU-based calculations are typically 9∼11 times faster than the corresponding sequential execution and approximately 1.5∼2 times faster than 16 CPU cores clusters implementations. On the basis of the simulated results, the comparisons between the theoretical results and the experimental ones are executed, and the good agreement between the two and more complete and larger cluster structures in the actual macroscopic materials are observed. Moreover, different nucleation and evolution mechanism of nano-clusters and nano-crystals formed in the processes of metal solidification is observed with large-sized system.

Quantifying the effect of solid phase composition and structure on solid–liquid partitioning of siderophile and chalcophile elements in the iron–sulfur system

We report experimentally determined partition coefficients between solid and liquid phases for bulk compositions on either side of the Fe–FeS eutectic for a suite of siderophile, chalcophile, and lithophile elements. Experiments were performed at conditions of 1.5 and 2GPa in pressure (P), 1323K in temperature (T), and virtually identical eutectic sulfide liquid compositions in equilibrium with either solid face centered cubic Fe or solid FeS. This enabled isolation of the effect of solid phase composition and structure from pressure–temperature–melt composition effects. Solid phase–liquid metal partition coefficients (D values) for Ge, Re, Ni, Co, Cr, Mn, V, Sn, Pb, Re and W differ significantly if partitioning occurs between identical metallic liquids but different solid phases, whereas Zn, Cu and Mo are virtually unaffected. For all elements except Ge and Sn, measured solid Fe–liquid sulfide partition coefficients at 1.5 and 2GPa are inconsistent with model predictions based on atmospheric pressure experiments, indicating that such models may not be appropriate for modeling core crystallization processes at non-ambient pressure.The framework of a lattice strain-based model of solid–liquid metal partitioning (Stewart et al., 2009) enables us to quantify the effect of the solid phase. Changing the solid phase from Fe to FeS leads to systematic increases in r0 (from 1.54 to 1.65Å) and apparent Young's modulus E (from 112 to 178GPa). These systematic changes can be used to predict element partitioning in eutectic solid FeS-bearing systems from measurements in eutectic solid Fe-bearing systems. Although changing the solid phase from face centered cubic Fe to FeS is an end member example, our data suggest that changes with pressure in the structure (e.g., to hexagonally close packed at high pressure) and composition (e.g. to higher S content at high pressure) of solid iron could affect the partitioning of elements between Fe and liquid metal during the solidification of planetary cores.

A fast simulation of transient metal flow and solidification in a narrow channel. Part I: Model development using lubrication approximation

A fast numerical algorithm for modelling transient flow and solidification of liquid metal in a narrow gap is presented. The problem is closely related to the die-cast process, and, in particular, to metal flow in thin ventilation channels. After integrating over the channel thickness and employing the lubrication approximation, the Navier–Stokes equations are reduced to 2-D equations for modelling the in-plane flow. The flow model is solved along with a heat balance equation after including the effects of solidification in a control volume. The flow variables and temperature distribution are solved in three stages. In step one, commercial software FLOW3D® is used to solve 3-D Navier–Stokes equations coupled with the heat balance equation for flow and solidification in the main cavity. In step two, the flow and heat transfer variables from the main model are transferred as the entrance boundary condition for the proposed numerical simulation. Finally, in step three, the metal flow and solidification in a thin channel is modelled using the 2-D equations coupled with the 1-D heat balance equation. Since the solid–liquid interface introduces non-linearity in the flow, the 2-D flow equations are solved iteratively while a staggered grid arrangement as required by the SIMPLE algorithm is used for discretization. Later in part II, the proposed simulation is applied to predict parts produced by the high pressure die cast process (HPDC). The model is validated by comparing its results with those obtained from the commercial flow-and-solidification software Flow3D® as well as with the experimentally measured Secondary Dendrite Arm Spacing (SDAS).

A Fast Numerical Simulation for Modeling Simultaneous Metal Flow and Solidification in Thin Cavities Using the Lubrication Approximation

A numerical algorithm for modelling steady flow of liquid metal accompanied by solidification in a thin cavity is presented. The problem is closely related to a die cast process and in particular to the metal flow phenomenon observed in thin ventilation channels. Using the fact that the rate of metal flow in the channel is much higher than the rate of solidification, a numerical algorithm is developed by treating the metal flow as steady in a given time-step while treating the heat transfer in the thickness direction as transient. The flow in the thin cavity is treated as two dimensional after integrating the momentum and continuity equations over the thickness of the channel, while the heat transfer is modelled as a one-dimensional phenomenon in the thickness direction. The presence of a moving solid-liquid interface introduces non-linearity in the resulting set of equations, and which are solved iteratively. The location and shape of the solid-liquid interface are found as a part of the solution. The staggered grid arrangement is used to discretize the flow governing equations and the resulting set of partial differential equations is solved using the SIMPLE algorithm. The thickness direction heat-transfer problem accompanied by phase change is solved using a control volume formulation. The results are compared with the predictions of the commercial software FLOW3D® which solves the full three-dimensional set of flow and heat transfer equations accompanied with solidification. The Reynolds's lubrication equations accompanied by the through-the-thickness heat loss and solidification model can be successfully implemented to analyze flow and solidification of liquid metals in thin channel during the die cast process. The results were obtained with significant savings in CPU time.

Effects of Ce Addition on the Mobility and Hot Tearing Tendency of Al-4.5Cu Alloy

This paper aims to study the effects of rare earth Cerium addition on mobility, solidification shrinkage, casting microstructure and hot tearing tendency of Al-4.5Cu alloy. Results show that by adding appropriate rare earth Cerium into the Al-4.5Cu alloy, the viscosity of liquid metals can be reduced, the mobility of alloy can be increased, and the shrinkage during the solidification of liquid metal can be reduced. Further more, as the tendency of alloy dendrite is inhibited and the microstructure of the casting alloy is improved, the alloy can be purified, its thermal conductivity can be enhanced, and the hot tearing tendency of it can be decreased remarkably. It proves that when rare earth Ceriumaddition in Al-4.5Cu alloy is 4w%, the mobility of Al-4.5Cu alloy will be the maximum, and its volume shrinkage will be the least. Meanwhile, the grains of alloy are refined and round. The alloy also shows the lowest hot tearing tendency.