Pure Melt Research Articles

A novel WC\u2013W2C composite synthesis by arc plasma melt cast technique: microstructural and mechanical studies

WC–W2C composites of three different compositions have been synthesized from mixture of WC + W (0, 5 and 16 wt% W) by thermal arc plasma melt-cast technique. Various grown phases observed in the composites consisting of major phases of WC and W2C and minor phases of unbound C (graphite) and tungsten (W) were confirmed by X-ray diffraction, selected area electron diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared studies. Transmission electron microscopy and field emission scanning electron microscopy show polycrystalline nature of composites. Energy dispersive spectroscopy (of X-ray) infers the absence of any impurity in the composite. Almost porous free nature of composites were observed from X-ray micro computed tomography and BET analysis studies. WC–W2C composite (16 wt% W) shows 25% and 21% higher micro hardness (2535 VHN) and Young’s modulus (625 GPa) values than that of pure melt cast WC sample.

Pure sediment-derived granites in a subduction zone

Abstract The Earth is unique in the Solar System due to significant volumes of granite in the lithosphere. However, the origins of granites are still highly debated, especially sediment-derived granites, which are often treated as a geochemical end-member of the continental crust. In the Yunnan region of South China, we identify the occurrence of pure sediment-derived granite in a subduction system. The suite of strongly peraluminous granite reported herein is interpreted to represent pure metasedimentary melts based on their whole-rock elemental and Sr-Nd-B and zircon Hf-O isotopic compositions. These Late Permian–Early Triassic (ca. 254–248 Ma) granites are characterized by radiogenically enriched Sr, Nd, and Hf isotopic signatures. They show δ11B and δ18O signatures akin to those of continental shales. Geochemical modeling indicates no contributions from the mantle that can be detected. Considering the regional tectonic evolution, these granites are suggested to be formed in a subduction zone by decompression melting of rapidly exhumed back-arc sediments. We posit that decompression melting was triggered by widespread extension and thinning of the crust prompted by rollback of the subducting oceanic crust. These granites thus provide evidence that granite formation in subduction zones does not necessarily contribute to crustal growth. These subduction-related pure sediment-derived granites have different elemental ratios and contents (e.g., Al2O3/TiO2 and Yb) from the Himalayan leucogranites. Considering their source compositions (e.g., pelitic rocks), which are similar to those of the Himalayan leucogranites, these differences are likely due to their higher formation temperature and lower pressure despite a great similarity in isotopic compositions. Identification of pure sediment-derived, strongly peraluminous granites (SPGs) in subduction systems provides an important geodynamic mechanism for crustal anatexis, which can both geochemically and tectonically complement their collisional counterparts identified in the Himalayas.

Multiple objects interacting with a solidification front

The interaction of objects suspended in a liquid melt with an advancing solidification front is of special interest in nature and engineering sciences. The front can either engulf the object into the growing crystal or repel it. Therefore, the object-front confrontation can have a strong influence on the microstructure and mechanical or functional properties of the solidified material. The past theoretical models and experimental studies have mostly investigated the interaction of isolated, spherical, and hard objects in pure melts. However, the outcome of object-front interactions in complex (more realistic) systems, where multiple objects and solutes are present, is still poorly understood. Here we show the interaction of multiple oil droplets with an ice-water front in the absence and presence of solute effects using in situ cryo-confocal microscopy. We report on how the object size, number of objects, and bulk solute concentration influence the the object-front interaction and the front morphology, as well as the subsequent object spatial distribution. We suggest that the volume fraction of objects suspended in a liquid melt in conjunction with the amount of bulk solute concentration are two important parameters to be incorporated in the development of object-front interaction models.

Atomic structure, diffusivity and viscosity of Al1-xMgx melts from ab initio molecular dynamics simulations

Atomic structure, diffusivity and viscosity of Al1-xMgx (x=0, 0.0039, 0.1172, 0.9180, 0.9961, 1)melts at 875, 1000, 1125, and 1250K were investigated by the ab initio molecular dynamics (AIMD) simulations. The simulated results are compared with available experimental and calculated data in the literature with reasonable agreements. Considering the results of pair correlation function g(r), it can be observed that Mg atoms in Al0.8828Mg0.1172 melt aggregate more obviously at 1000 and 1250K. For Al0.0820Mg0.9180, Al atom segregation is more obvious at 875 and 1000K. The tracer diffusion coefficients of Al or Mg in Al1-xMgx (x=0.1172, 0.9180) melts, and interdiffusion coefficients of Al0.8828Mg0.1172 and Al0.0820Mg0.9180 melts are all close to the self-diffusion coefficients of Al or Mg. With the increasing temperature, the diffusivity increases linearly. In dilute melts, the tracer diffusion coefficients of solute atom and the interdiffusion coefficients increase nonlinearly with the increasing temperature. For Al0.8828Mg0.1172 and Al0.0820Mg0.9180 melts, the viscosities ? are comparatively higher than pure melts. The viscosities of all melts decrease with the increasing temperature, then increase at 1250K. The results obtained in the present work provide an insight into the design of Al and Mg alloys.

Hybrid granite magmatism during orogenic collapse in the Eastern Desert of Egypt: Inferences from whole-rock geochemistry and zircon U–Pb–Hf isotopes

Granites can provide detailed insights into crust formation and reworking during the different stages of orogenic cycles. New field and petrographic observations are integrated with whole-rock geochemical and zircon U-Pb and Hf isotopic data of granitic and subvolcanic felsite intrusions associated with the Atalla Shear Zone (ASZ). Formation of the ASZ is attributed to regional oblique convergence, late in the tectono-magmatic evolution of the Central Eastern Desert of Egypt. The new data reveal three stages of post-collisional felsic magmatism, with a change in magma type from I- to A-type granites. The evolution commenced with formation of quartz-monzodiorite and granodiorite at 639 ± 2 Ma (stage 1), followed by a suite of granodiorite to syenogranite intrusions between 619 ± 2 and 612 ± 2 Ma (stage 2), and ceased with the Atalla felsites at 607 ± 2 Ma (stage 3). During stages 1 and 2, the ASZ was intruded by hybrid granites as a result of mixing of lower crust material with mantle-derived mafic sanukitoid-like melts, in addition to nearly pure crustal melts during stage 2. The Atalla felsites, with distinct A-type affinities, are interpreted to have resulted from fractional crystallization of hybrid magmas in shallow crustal levels prior to emplacement. The identical initial Hf isotope compositions of all ASZ-associated magmatic rocks imply that the crust and mantle reservoirs had similar Hf isotopic composition at ~640–610 Ma (εHf(t) = 8 ± 1). This implies that mantle enrichment was controlled largely by subducted Neoproterozoic oceanic crust, volcanic arc, and syn-collisional rocks. The new U-Pb ages combined with the geochemical characteristics of the ASZ granitic rocks are consistent with a prolonged period of decompression melting of hitherto enriched mantle and lower crust. Melting was likely triggered by rejuvenation of thoroughgoing transcurrent shearing and shear-driven asthenospheric mantle upwelling during the orogenic collapse stage.

Petrogenesis of the F-rich peraluminous A-type granites: An example from the Devonian Achala batholith (Characato Suite), Sierras Pampeanas, Argentina

The Characato suite (Achala batholith, Sierras Pampeanas, Argentina), consists of at least six granitic facies with affinities of F-rich moderately to strongly peraluminous A-type granites. The two more extensive facies (Facies 1 and 2) and a minor one (Facies 5) would represent at least three batches of magma generated by partial melting from the same source but at different times and under different P-T conditions. Previous and new U-Pb zircon ages for the Characato suite suggest that these granites crystallized between 366 ± 3 and 359 ± 5 Ma. U-Pb inherited zircon ages, Th/U ratios and the whole-rock Sr-Nd isotopic compositions indicate that the source is predominantly composed of Early Cambrian S-type granites and diatexites and minor Early Ordovician TTG granitoids, which formed part of the Devonian deep crust of the Sierras de Córdoba. Mineral saturation thermometers, phase equilibrium modeling and trace element modeling suggest that the Facies 1 comprise magmas generated at ~ 0.5 GPa and ~805°C and least evolved Facies 2 (+ Facies 5) comprise magmas generated at ~ 0.7 GPa and ~870°C: both could represent low proportions of pure melts (~10% to ~20%) that contain minor amounts of entrained residual mineral phases. Fractional crystallization models may explain the chemical variation in the evolved granitic samples (Facies 2, 3, 4 and 6) by fractional crystallization of plagioclase, K-feldspar, quartz, biotite, muscovite, zircon, monazite and Fe-Ti-oxides. Facies 6, composed of high evolved granitic rocks, probably represents the late stages of the fractional crystallization process where late fluids interacted with the magmas.

Threading-Unthreading Transition of Linear-Ring Polymer Blends in Extensional Flow.

Adding small amounts of ring polymers to a matrix of their linear counterparts is known to increase the zero-shear-rate viscosity because of linear-ring threading. Uniaxial extensional rheology measurements show that, unlike its pure linear and ring constituents, the blend exhibits an overshoot in the stress growth coefficient. By combining these measurements with ex-situ small-angle neutron scattering and nonequilibrium molecular dynamics simulations, this overshoot is shown to be driven by a transient threading-unthreading transition of rings embedded within the linear entanglement network. Prior to unthreading, embedded rings deform affinely with the linear entanglement network and produce a measurably stronger elongation of the linear chains in the blend compared to the pure linear melt. Thus, rings uniquely alter the mechanisms of transient elongation in linear polymers.

Theory of microstructure-dependent glassy shear elasticity and dynamic localization in melt polymer nanocomposites.

We present an integrated theoretical study of the structure, thermodynamic properties, dynamic localization, and glassy shear modulus of melt polymer nanocomposites (PNCs) that spans the three microstructural regimes of entropic depletion induced nanoparticle (NP) clustering, discrete adsorbed layer driven NP dispersion, and polymer-mediated bridging network. The evolution of equilibrium and dynamic properties with NP loading, total packing fraction, and strength of interfacial attraction is systematically studied based on a minimalist model. Structural predictions of polymer reference interaction site model integral equation theory are employed to establish the rich behavior of the interfacial cohesive force density, surface excess, and a measure of free volume as a function of PNC variables. The glassy dynamic shear modulus is predicted to be softened, reinforced, or hardly changed relative to the pure polymer melt depending on system parameters, as a result of the competing and qualitatively different influences of interfacial cohesion (physical bonding), free volume, and entropic depletion on dynamic localization and shear elasticity. The localization of polymer segments is the dominant factor in determining bulk PNC softening and reinforcement effects for moderate to strong interfacial attractions, respectively. While in the athermal entropy-dominated regime, the primary origin of mechanical reinforcement is the stress stored in the aggregated NP subsystem. The PNC shear modulus is often qualitatively correlated with the segment localization length but with notable exceptions. The present work provides the foundation for developing a theory of segmental relaxation, Tg changes, and collective NP dynamics in PNCs based on a self-consistent treatment of the cooperative activated motions of segments and NPs.

Conformations and Dynamics of Polymer Chains in Cis and Trans Polybutadiene/Silica Nanocomposites through Atomistic Simulations: From the Unentangled to the Entangled Regime

The conformations and the dynamics of poly(butadiene) (PB) chains, of various molecular weights, in PB/silica nanocomposites are studied through long-time atomistic molecular dynamics simulations at T = 413 K, well above Tg. The effect of the stereochemistry of PB chains is addressed by simulation of cis-1,4-PB/silica and trans-1,4-PB/silica nanocomposites. The model systems contain 30 wt % (≈12 vol %) silica nanoparticles (NPs) of diameter ≈4 nm. The nanocomposites are characterized through analyzing (i) interfacial packing and the dimensions of the PB chains; (ii) statistics of the train, bridge, loop, and tail conformations of adsorbed chains and the coupling between segmental orientational dynamics and chain conformations; and (iii) the orientational and translational dynamics of the polymer chains and the desorption kinetics of chains and segments. The dimensions of PB chains, excluding a small fraction of chains that wrap around the NP, are not affected. The segmental and terminal dynamics of PB chains are slower in the nanocomposites than in the respective bulk melts. Moreover, the dynamics of PB chains in the nanocomposites is very heterogeneous, and a coupling between the dynamics and the conformation of PB chains is observed: the adsorbed segments (trains) and the chains that have a higher number of contacts to the NPs are more decelerated. Additionally, at long times, bridge segments exhibit a very slow orientational decorrelation. The self-diffusion coefficients, D, of PB chains in the nanocomposites are also reduced compared to the respective bulk systems. A clear crossover from the unentangled (Rouse-like) to the entangled (reptation-like) regime is observed based on the calculation of the segmental mean-square displacement and D as a function of the chain length. The effective tube diameter of entangled PB chains in the nanocomposites is estimated to be slightly smaller than in the pure melts. The deceleration of dynamics in the nanocomposites, in both Rouse and reptation-like regimes, is discussed in terms of a higher effective monomeric friction coefficient. Finally, the correlation times for the desorption of segments and chains are much larger than the segmental and end-to-end-vector correlation times, respectively.

The compositional variation of I-type granites: Constraints from geochemical analyses and phase equilibrium calculations for granites from the Qinling orogen, central China

There is a large compositional variation of I-type granites. Although partial melting and fractional crystallization are the two primary mechanisms for the variation, it is intriguing to know how they jointly work. This issue is addressed by a combined study of geochemistry and phase equilibrium modelling for a Triassic pluton from the Qinling orogen. The pluton consists of high-K, calc-alkaline I-type granites. Geochemical results suggest that the granites are likely sourced from Triassic mafic-intermediate igneous rocks. Compared with experimental melts, it is inferred that the natural granites are not the crystallized product from pure magmatic melts. This is confirmed by phase equilibrium calculations that have utilized the Triassic mafic-intermediate igneous rocks as the source, yielding modelled melts that contain too low FeOt, MgO and Mg# to match the target granites. The addition of restitic mineral assemblages to melts can relieve the discrepancy, but the modelled magmas have much higher CaO than the granites. Replacing equilibrium melting by disequilibrium melting in terms of the plagioclase behavior can lead to a satisfactory match. Furthermore, by taking the average of the target granites as a parental magma, the modelled crystalline products can well reproduce the variation trends in the high-K, calc-alkaline I-type granites from the Qinling orogen. In this regard, the crustal anatexis would produce the parental magma at first, which experienced fractional crystallization to form the granitic pluton with the compositional variation as observed. Therefore, these two processes would jointly lead to the compositional variation of I-type granites in nature.

Microstructural Evolution and Growth of Intermetallic Compounds at the Interface between Solid Cast Iron and Liquid Al–Si Alloy

Compound casting has received a great deal of attention as a useful method for fabricating a single complicated part from dissimilar metallic materials. For example, in the case of automobile cylinder blocks, research is being carried out to compound cast iron with aluminum alloys. In order to manufacture such as composite parts, it is essential to control the intermetallic compound formed at the interface between two metals. In this research, the type and growth behavior of compounds formed at the interface between cast iron and aluminum, or Al–Si alloy, were investigated. It was observed that the Al5Fe2 phase was mainly formed at the interface between the pure aluminum melt and the solid cast iron, and the thickness of the interfacial compound increased proportionally with increasing contact time. On the other hand, more complex phases were formed at the interface between the Al–Si alloy melt and the solid cast iron. In the case of a specimen having a contact time of 10 min, Al4.5FeSi, Al8Fe2Si and Al5Fe2 phases appeared to occupy the largest portion of the interfacial compound region. The total thickness of the interfacial compounds also increased in proportion to the contact time.

Threading-Induced Dynamical Transition in Tadpole-Shaped Polymers.

The relationship between polymer topology and bulk rheology remains a key question in soft matter physics. Architecture-specific constraints (or threadings) are thought to control the dynamics of ring polymers in ring–linear blends, which thus affects the viscosity to range between that of the pure rings and a value larger, but still comparable to, that of the pure linear melt. Here we consider qualitatively different systems of linear and ring polymers, fused together in “chimeric” architectures. The simplest example of this family is a “tadpole”-shaped polymer, a single ring fused to the end of a single linear chain. We show that polymers with this architecture display a threading-induced dynamical transition that substantially slows chain relaxation. Our findings shed light on how threadings control dynamics and may inform design principles for chimeric polymers with topologically tunable bulk rheological properties.

Effects of valence and spin of Fe in MgSiO3 melts: Structural insights from first-principles molecular dynamics simulations

Iron (Fe) is present in terrestrial melts and at all depths inside the Earth. How Fe in its varying oxidation and spin states influences the properties of silicate melts is of critical importance to the understanding of the chemical evolution of our planet. Here, we report the results of first-principles molecular dynamics simulations of molten Fe-bearing MgSiO3 over a wide pressure range covering the entire mantle. Our results suggest that the structural properties of the host melt, such as the average bond length and coordination in Mg–O and Si–O do not differ much when compared with the pure melt. More importantly, they show that the local Fe–O structure is more sensitive to the spin state (high-spin, HS and low-spin, LS) of iron than to its valence state (Fe2+ and Fe3+). For iso-valence configurations, the average Fe–O bond length and coordination number differ by more than 10% and ∼30%, respectively, between the HS and LS states. In comparison, the corresponding differences between Fe2+ and Fe3+ for iso-spin configurations are within 5 and 15%, respectively. Ferrous iron shows lower average oxygen coordination numbers of ∼3.8 for HS and ∼3.3 for LS compared to the corresponding numbers of ∼4.1 and ∼3.7 for ferric iron at 0 GPa and 3000 K. As pressure increases, the coordination gap between the ferrous and ferric iron closes for HS but persists for LS. Our analysis of the proportions of non-bridging and bridging oxygens and the rates of bond breaking/formation events suggests an equivalent role of the ferrous and ferric iron in terms of their network forming ability. The predicted structural behavior of iron in its different oxidation states is generally consistent with the experimental inferences for MgO–FeO–SiO2 melts. Unlike other ferrosilicate compositions for which the experimental data suggest that Fe3+ increases and Fe2+ decreases the viscosity of the melt, the ferrous and ferric iron, due to their structural equivalence, are likely to have a similar influence on the dynamical behavior of deep mantle iron-bearing MgSiO3 melts.

The pre-hot dipping effects on the bimetal casting of nitriding steel sleeve into the Al-Si matrix

Steel-aluminum composite material combine the excellent mechanical properties of steel such as high strength and good wear resistance with the advantages of lightweight aluminum for widely using in automobile engine block, gearbox and other car body structures. In this paper, a new process is used to cast the alloy steel sleeve into Al-Si alloy matrix for preparing aluminum engine block with steel cylinder liner. The process consists of three parts: the surface pre-treatment of steel, the hot-dipping melt and solid-liquid casting of steel with aluminum. Generally, the hot dipping melt should have lower melting point than the melting point of aluminum alloy, good temperature oxidation resistance and amount of solid solubility both with steel and aluminum. Giving consideration of such condition and cost, Zn´ Al and its alloys are used in present paper for learning the effect of hot dip coating melts on the interface properties of steel/aluminum at different times. After hot dipping, a coating formed on the surface of the steel bushing, which improves its wettability in the aluminum melt and the metallurgical bonding effect of the steel-aluminum interface. The microstructure, phase composition, growth kinetics and hardness distribution of the interface were analyzed by metallographic microscopy, scanning electron microscopy with EDS. The results show that the metallurgical bonding interface of steel/aluminum bimetal casting can be obtained by hot dipping. Hard-brittle diffusion layer produced by dipping pure Al is thicker than that produced by ZL101. Dipping pure zinc produces a dense intermetallic layer of 3-5 um and a large amount of dispersed phase of Al3FeZnx, and the bonding performance of such interface is better than the other two. The interface hardness of steel-aluminum bimetal casting obtained by hot dipping pure Al melt, ZL101 melt and pure Zn melt can reach 563.5HV, 528.3HV and 632.3HV, respectively.

Dynamic Heterogeneity in Ring-Linear Polymer Blends.

We present results from a direct statistical analysis of long molecular dynamics (MD) trajectories for the orientational relaxation of individual ring molecules in blends with equivalent linear chains. Our analysis reveals a very broad distribution of ring relaxation times whose width increases with increasing ring/linear molecular length and increasing concentration of the blend in linear chains. Dynamic heterogeneity is also observed in the pure ring melts but to a lesser extent. The enhanced degree of dynamic heterogeneity in the blends arises from the substantial increase in the intrinsic timescales of a large subpopulation of ring molecules due to their involvement in strong threading events with a certain population of the linear chains present in the blend. Our analysis suggests that the relaxation dynamics of the rings are controlled by the different states of their threading by linear chains. Unthreaded or singly-threaded rings exhibit terminal relaxation very similar to that in their own melt, but multiply-threaded rings relax much slower due to the long lifetimes of the corresponding topological interactions. By further analyzing the MD data for ring molecule terminal relaxation in terms of the sum of simple exponential functions we have been able to quantify the characteristic relaxation times of the corresponding mechanisms contributing to ring relaxation both in their pure melts and in the blends, and their relative importance. The extra contribution due to ring-linear threadings in the blends becomes immediately apparent through such an analysis.

Revisiting tin melting for phase change model verification

Model verification is necessary before numerical models can be applied to produce meaningful results. For solid-liquid phase change modelling involving convection, pure gallium and tin melting have been widely used as reference for verification. It was later found that contrasting observations have been reported on the flow structure of both metals in the liquid region during the phase change process. Some researchers have reported monocellular while others reported multicellular structures in past works. In this work, tin melting problem was revisited by extending the results to flow structure visualization with Line Integral Convolution (LIC) plots to confirm the flow structure for tin melting thus pure metals in general. Enthalpy-porosity formulation coupled with Finite-Volume Method (FVM) was used to solve the set of governing equations which represented the problem at Prandtl Number = 0.02, Stefan Number = 0.01 and Rayleigh Number = 2.5 x 105. The location of solid-liquid interface and LIC plots at different times were presented. At initial state, the solid-liquid interface was closely similar for all grid sizes but as time progresses, finer grids provided improved solutions as expected. Reasonable fine grid size must be selected for solid-liquid phase change models to ensure complete physics of the problems are captured and eventually yield acceptable numerical results. The LIC plots confirmed that the flow structure is multicellular. Future phase change models referring to pure metal melting problem for verification should obtain similar flow structure to be considered acceptable.

Flow‐to‐Sliding Transition in Crystal‐Bearing Magma

AbstractThe presence of crystals in magmatic flows introduces spatial heterogeneity, which can build up to the degree that the flow behavior of the crystal‐bearing magma becomes substantially different from that of a pure melt. One example is the transition from flow to sliding, in which the deformation in the crystalline magma is concentrated almost entirely in a thin interfacial layer as opposed to being distributed in a typical flow profile throughout the domain. In this study, we use numerical reproductions of existing laboratory experiments of Fuji basalt in a rotational viscometer to identify when the flow‐to‐sliding transition is likely to occur in crystal‐bearing magma. We utilize a direct numerical method to resolve the interactions between the crystals and the magmatic melt at the scale of individual interfaces in 2‐D. All phase interactions and their aggregate effects on the flow emerge self‐consistently from the simulation itself. We find that the long‐range hydrodynamic interactions between crystals create nonlinear flow behavior even at low crystal fractions. By performing simulations in different geometries, we show that the formation and stability of force chains in crystal‐bearing magma depend sensitively not only on the crystal shape and size but also on the geometry of the experimental apparatuses. Our simulations are consistent with the observed discrepancies in previous laboratory measurements of shear thinning behavior, highlighting the delicacies of using point measurements in experiments to constrain the bulk rheology of crystal‐bearing magma.

Thermal conductivity and thermal diffusivity of Li-Pb eutectic in the temperature range of 293–1273 K

Thermal conductivity (λ) and thermal diffusivity (a) of an Li-Pb alloy of eutectic composition (with a Li content of 15.7 at.%) have been measured by the laser flash method in the range from room temperature to 1273 K. The error in the λ measurement was 3–5 % for solid and 4–6 % for liquid states. The data of this paper were compared with the results of other authors available in the literature. The thermal conductivity of the Li15.7Pb84.3 is shown to be lower than that of pure lead melt and to increase with temperature in both phases. Approximation equations and a table of reference values for the temperature dependence of λ, a have been obtained.

Numerical study of melting performance enhancement for PCM in an annular enclosure with internal-external fins and metal foams

Application of different heat transfer augmentation techniques, including the use of fins or foams, were investigated to enhance the melting rate of a solid phase change material within an annulus where the inner and outer pipes were subjected to constant wall temperature. The carbon fibre fins as well as three commonly-used foams (made of three different materials: nickel, aluminium and copper) were simulated. Firstly, keeping the total fin volume constant, the fin number density effect on the melting rate was investigated. After an optimal fin number density was obtained, three possible strategies (unequal length, uneven intervals and tree-shaped fins) were explored aimed at a more comprehensive understanding of the induced heat transfer enhancement. It was observed that with a fixed fin thickness and volume, the melting time is not a monotonic function of the fin number density and can be optimized. Comparing pure PCM melting, the use of optimized fin number reduced over 60% of melting time, while additional 8% and 4% further time reduction could be achieved by appropriately increasing lengths and decreasing intervals of bottom fins, respectively. The use of tree-like fins resulted in a longer melting time, comparing to that of longitudinal straight fins, which indicates it is not always a good option. Finally, the results, primarily the melting rates, were compared with those obtained through the use of metal foams with different metals. It was observed that the melting time of optimized strategy-1 is rather less than those of Cu and Al foams, and approximately 2200s shorter than that of Ni foams. These results indicate that the fins, if designed properly, can be as efficient as foams.

Effect of straining flow on growth of columnar crystal in ternary undercooled melt

As an important microstructure, columnar crystal growth technology, especially the growth technology of single columnar crystal plays an important role in improving the performances of semiconductor, optical devices and other related products. In many practical applications, because the alloy is composed of multi-component and there is inevitably flow in the melt, it is necessary to study the growth of columnar crystals in multi-component melt with flow separately. The growth of columnar crystal in a ternary undercooled melt subjected to straining flow under non-isothermal conditions is studied, and the approximate analytical expression for growth morphology of columnar crystal is given by using asymptotic method. It can be seen from the expression that straining flow is an important reason for irregular columnar crystal. When analyzing the effect of straining flow on the growth of columnar crystal in ternary melt, it is found that the incoming flow accelerates the growth velocity of the interface, while the outgoing straining flow reduces the growth velocity of the interface, namely, the straining flow makes the interface of columnar crystal deformed. At the same time, it is found that the interface deformation becomes more intense with the increase of flow velocity. The above conclusion can also be applied to the effect of straining flow on the interface morphology of columnar crystal in pure melt and binary melt. The comparison of the effects of straining flow on the interface of columnar crystal among pure melt, binary melt and ternary melt, shows that the interface morphology of columnar crystal in dilute alloy melt is more affected by straining flow than in the pure melt, but the more components are more easily affected by flow. However, the number of components in melt is not a decisive factor for the change of interface morphology of the columnar crystal, but the constitutional undercooling is an important factor for determining the interface morphology of multicomponent alloy. According to the conclusion of this paper, the influence of straining flow on the interface morphology of columnar crystal growth can be quantitatively predicted, which provides the necessary theoretical guidance in accurately controlling the interface morphology in the future.