Numerical simulation of fluid flow and alloy melting in RH process for electrical steels

Based on the Eulerian-Lagrangian approach,a mathematical model was established to describe the gas-liquid flow behavior in the Ruhrstahl-Heraeus(RH)degasser.The momentum source and the turbulent kinetic energy source due to the motion of gas bubbles were considered for the liquid flow.The effect of the expansion of gas bubbles on the liquid velocity,recirculation rate,and mixing time was quantitatively evaluated.After the fluid flow reached the steady state,the melting and mixing processes of aluminum alloys in the RH degasser were also investigated.The results indicate that the expansion of gas bubbles has a significant infuence on the recirculation rate and the mixing time in the RH process.Increasing the superheat of liquid steel and decreasing the initial diameter of alloy particles are beneficial to promote the melting and mixing of alloy particles.Due to the existence of solidified steel shells,the maximum diameter of the alloy particle is about 1.5 times its initial diameter.

Electromagnetic Filtration of Primary Fe-Rich Phases from Al-Si Alloy Melt

Electromagnetic filtration of primary Fe-rich phases (complex compound of AlFeSiMn) from Al-Si alloy melt containing 1.2 wt pct Fe have been studied by theoretical analysis and on a self-designed electromagnetic filtration equipment. The principle of the electromagnetic filtration is that the EMF (electromagnetic force) scarcely acts on the primary Fe-rich phases having low electric conductivity, which are then moved in the direction opposite to that of the EMF. Experimental results show that the primary Fe-rich phases are separated from Al-Si alloy melt and are collected in the filter while the melt is in horizontal flow. The removal efficiency of the primary iron-phases (77) calculated is less as the greatest flow velocity of the melt (UM) and the height of the filter (2h) are larger, while it becomes larger as EMF, operating distance of electromagnetic force (cr) and particle size (dv) become larger. It has been confirmed that the primary iron-phases larger than 20 jim can be removed efficiently by theoretical analysis and experiments. This new technique is high efficient and available for continuously flowing melts as compared with natural settling and filtration methods, which offer a possibility for recycling high quality aluminum alloys.

TEMPERATURE DEPENDENCE OF VISCOSITY OF Al-Si ALLOY MELTS

The relationship between the viscosity and temperature of Al-Si alloy melts was investigated. The viscosity of three different types of Al-Si alloy melts was measured. It was showed that the relationship between the viscosity and temperature of hypoeutectic Al-5%Si and eutectic Al- 12.5%Si alloy melts is approximately exponential except for some special zones, but that of the hypereutectic melt is different. The paper discussed the correlation of the viscosity and atomic density, which is thought that the viscosity corresponds to the atomic density to some extent.

Specific heat of superheated Al-10Sr alloy melts

The specific heat of superheated Al 10Sr melts was determined at different heating rates between 1 K/min and 20 K/min using a differential scanning calorimeter(DSC). As a whole, the specific heat increases with increasing temperature. A hump is observed on the specific heat curve at the temperature corresponding to the phase boundary temperature dependent on heating rate. Moreover, the hump shifts to higher temperature in the measured temperature range from about 840 ℃ to 890 ℃ with increasing heating rate. At certain temperature in the higher superheated zone, the specific heat of the melt as a function of temperature shows a sharp rise . The result indicates that disorder zone fraction begins to increase while atom clusters fraction decreases at the breaking temperature. [

Electrical Properties of GeTe-based Ternary Alloys

Ge_（50-x）Sb_xTe_（50） and Ge_（50-x）Bi_xTe_（50） ternary alloys were synthesized by vacuum melting at 1273 K with the starting materials of Ge, Bi, Sb, and Te. The lattice structures were analyzed based on X-ray diffraction patterns, which could all be indexed to R3m rhombic structure. Electrical properties measurements revealed that the Ge-Sb-Te ternary alloys were p-type semiconductors with high electrical conductivity of 4.5×10~5S？m^（-1） near room temperature. And the maximum electrical property was obtained at Ge_45Sb_5Te_50, with the power factor of 2.49×10^（-3）W？m^（-1）K^（-2） at 640 K. Due to the existence of secondary phases, the electrical conductivity of Ge-Bi-Te system was lower and Seebeck coefficient was higher comparing with those of Ge-Sb-Te system.

Simulation of Dendritic Growth with Melt Convection in Solidification of Ternary Alloys

A cellular automaton-lattice Boltzmann coupled model is extended to study the dendritic growth with melt convection in the solidification of ternary alloys. With a CALPHAD-based phase equilibrium engine, the effects of melt convection, solutal diffusion, interface curvature and preferred growth orientation are incorporated into the coupled model. After model validation, the multi dendritic growth of the Al-4.0 wt%Cu-1.0 wt%Mg alloy is simulated under the conditions of pure diffusion and melt convection. The result shows that the dendritic growth behavior, the final microstructure and microsegregation are significantly influenced by melt convection in the solidification.

Relationship between Voronoi entropy and the viscosity of Zr_(36)Cu_(64) alloy melt based on molecular dynamics

Molecular dynamics simulation is used to investigate the relationship between Voronoi entropy and viscosity for rapid solidification processing of Zr36Cu64 binary alloy melt. The simulation results at different temperatures, cooling rates, and pressures, show that Voronoi entropy is able to accurately describe the relationship of the transition between the cluster structure and the viscosity of Zr36Cu64 binary alloy melt through Voronoi polyhedron analysis. That is, the higher the degree of order of the microstructure, the lower the Voronoi entropy is and the higher the viscosity is. The simulation provides an important reference for studying metallic glass with high glass-forming ability.

Ab initio study of dynamical properties of U-Nb alloy melt

The U-Nb alloy,as a kind of nuclear material with good corrosion resistance and mechanical properties,plays an important role in the nuclear industry.However,the experimental measurements and theoretical calculations of many parameters which are essential in describing the dynamical properties of this alloy melt,including density,diffusivity,and viscosity,have not been carried out yet.The lack of data on the dynamical properties of nuclear materials seriously hinders the high-performance nuclear materials from being developed and applied.In this work,the dynamical properties of the U-Nb alloy melt are systematically studied by means of ab initio molecular dynamics simulations and their corresponding mathematical models are established,thereby being able to rapidly calculate the densities,diffusion coefficients,viscosities,and their activation energies in the whole U-Nb liquid region.This work provides a new idea for investigating the dynamical properties of binary alloy melts,thereby promoting the development of melt research.

Highly Improved Electrochemical Performances of the Nanocrystalline and Amorphous Mg_2Ni-type Alloys by Substituting Ni with M (M=Cu,Co,Mn)

The element Ni in the Mg2Ni alloy is partially substituted by M（M = Cu, Co, Mn） in order to ameliorate the electrochemical hydrogen storage performances of Mg2Ni-type electrode alloys. The nanocrystalline and amorphous Mg20Ni10-xMx（M = None, Cu, Co, Mn; x = 0-4） alloys were prepared by melt spinning. The effects of the M（M = Cu, Co, Mn） content on the structures and electrochemical hydrogen storage characteristics of the as-cast and spun alloys were comparatively studied. The analyses by XRD, SEM and HRTEM reveal that all the as-cast alloys have a major phase of Mg2Ni but the M（M = Co, Mn） substitution brings on the formation of some secondary phases, MgCo2 and Mg for the（M = Co） alloy, and Mn Ni and Mg for the（M = Mn） alloy. Besides, the as-spun（M = None, Cu） alloys display an entirely nanocrystalline structure, whereas the as-spun（M = Co, Mn） alloys hold a nanocrystalline/amorphous structure, suggesting that the substitution of M（M = Co, Mn） for Ni facilitates the glass formation in the Mg2Ni-type alloys. The electrochemical measurements indicate that the variation of M（M = Cu, Co, Mn） content engenders an obvious effect on the electrochemical performances of the as-cast and spun alloys. To be specific, the cyclic stabilities of the alloys augment monotonously with increasing M（M = Cu, Co, Mn） content, and the capacity retaining rate（S20） is in an order of（M = Cu） 〉（M = Co） 〉（M = Mn） 〉（M = None） for x≤1 but changes to（M = Co） 〉（M = Mn） 〉（M = Cu） 〉（M = None） for x≥2. The discharge capacities of the as-cast and spun alloys always grow with the rising of M（M = Co, Mn） content but first mount up and then go down with increasing M（M = Cu） content. Whatever the M content is, the discharge capacities are in sequence：（M = Co） 〉（M = Mn） 〉（M = Cu） 〉（M = None）. The high rate discharge abilities（HRDs） of all the alloys grow clearly with rising M（M = Cu, Co） content except for（M = Mn） alloy, whose HRD has a maximum value with varying M（M = Mn） content. Furthermore, for the as-cast alloys, the HRD is in order of（M = Co） 〉（M = Mn） 〉（M = Cu） 〉（M = None）, while for the as-spun（20 m·s^-1） alloys, it changes from（M = Co） 〉（M = Mn） 〉（M = Cu） 〉（M = None） for x = 1 to（M = Cu） 〉（M = Co） 〉（M = None） 〉（M = Mn） for x = 4.

Effect of Melt Quenching on Martensite Transformation in Fe-Ni Alloy

The main features of martensite transformation in melt-quenched Fe-31.4% Ni alloy on cooling below room temperature have been studied. It is found that the ribbon 50～60 μm thick, prepared by spinning technique, is a natural composite in which isothermal and surface martensite are not formed, while athermal martensite forms at lower temperature, all factors being the same, as compared to the alloy of the same composition and grain size, prepared by recrystallization.

Thermal Performance of Low-Melting-Temperature Alloy Thermal Interface Materials

Thermal resistance of low-melting-temperature alloy （LMTA） thermal interface materials （TIMs） was measured by laser flash method before and after different stages of heating. The results showed that the thermal performance of the LMTA TIMs was degraded during the heating process. It is suggested that the degradation may mainly be attributed to the interfacial reaction between the Cu and the molten LMTAs. Due to the fast growth rate of intermetallic compound （IMC） at the solid-liquid interface, a thick brittle IMC is layer formed at the interface, which makes cracks easy to initiate and expand. Otherwise, the losses of indium and tin contents in the LMTA during the interfacial reaction will make the melting point of the TIM layer increase, and so, the TIM layer will not melt at the operating temperature.

Direct manufacturing of Cu-based alloy parts by selective laser melting

The frequent defects of the metal parts, such as non-fully melting, thermal strain, and balling, which are produced by selective laser melting （SLM） that is a novel method of one-step manufacturing, are analyzed theoretically and experimentally. The processing parameters significantly affect the quality of the final parts, and simultaneously, the appropriate laser mode and the special scanning strategy assure a satisfying quality of the final parts. The SLM experiment is carried out using Cu-based powder. The metal part is divided into several scanned regions, each of which is scanned twice at the cross direction with different scanning speeds. The microstructure is analyzed on microscope. The results show that the part is metallurgically bonded entity with a relative density of 95%, and the microstructure is composed of equiaxial crystal and dendritic crystal whose distributions are mainly decided by the scanning strategy.

Research progress on solder thermal interface materials

Down to the road of miniaturization and high power density,the heat dissipation is becoming one of the critical factors restricting further development of advanced microelectronic devices.Traditional polymer-based thermal interface materials(TIMs) are not competitive for the high efficiency thermal management,mainly due to their low intrinsic thermal conductivity and high interface thermal resistance.Solder-based TIM is one of the best candidates for the next generation of thermal interface materials.This paper conducts a perspective review of the state of the art of solder TIM,including low melting alloy solder TIM,composite solder TIM and nanostructured solder TIM.The microstructure,process parameters,thermal performance and reliability of different TIMs are summarized and analyzed.The future trends of advanced TIMs are discussed.

Superelasticity of Cu–Ni–Al shape-memory fibers prepared by melt extraction technique

In the paper, a melt extraction method was used to fabricate Cu–4Ni–14Al（wt%） fiber materials with diameters between 50 and 200 μm. The fibers exhibited superelasticity and temperature-induced martensitic transformation. The microstructures and superelasticity behavior of the fibers were studied via scanning electron microscopy（SEM） and a dynamic mechanical analyzer（DMA）, respectively. Appropriate heat treatment further improves the plasticity of Cu-based alloys. The serration behavior observed during the loading process is due to the multiple martensite phase transformation.

Ab initio Molecular Dynamics Study of Local Atomic Structure Evolution of U–Zr Alloy Melts upon Solidification

We study the local atomic structure evolution of UZr and UZr_(2) alloy melts upon solidification through ab initio molecular dynamics simulations.This is achieved by analyzing in detail the temperature dependence of structure factors,pair correlation functions,the bond angle distributions,Honeycutt-Anderson index and Voronoi tessellation analysis as well as local bond orientation order parameters.We observe that as the temperature decreases the pair correlation functions and structure factors become more structured with clear distinctions at the liquid–solid phase transition temperature.The Honeycutt-Anderson indices and Voronoi tessellation analysis indicate that the liquid phase is predominantly comprised of the icosahedra-like local structures,whose fraction increases with decreasing temperature up to the transition temperature and then abruptly drops at the transition temperature,whereas the bcc-like local atomic structures dominate during the solidification process.Furthermore,the bond orientation order analyses with\({\overline{w}}_{6}\)–\({\overline{q}}_{6}\)correlation map and bond angle distribution imply that the local structures mainly consist of the bcc-type during the solidification below the transition temperature.All the analyses are consistent with each other,showing a first-order liquid to solid phase transition for both UZr and UZr_(2) solid solutions,which only differ in different predicted transition temperatures.This work provides a comprehensive insight into the detailed local structure evolution during the solidification of the U–Zr alloy melts at the atomic level.Similar strategies used here can be extended to studying the liquid–solid phase transition in other alloy systems.

Serrated chip characteristics and formation mechanism in high-speed machining of selective laser melted Ti6Al4V alloys

Serrated chips,consisting of extremely uneven plastic deformation,are a prominent feature of high-speed machining of difficultto-machine materials.This paper focuses on the evolution of chip form,chip morphology features(chip free surface,tool-chip contact surface,and chip edge),and chip segment parameters in subsequent high-speed(vc=50 and 150 m min-1)machining of selective laser melted(SLMed)Ti6Al4V alloys,which are significantly different from conventional Ti6Al4V alloy in microstructure,mechanical properties and machinability.The effect of laser beam scanning schemes(0°,67.5°,and 90°),machined surfaces(top and front),and cutting speeds on serrated chip characteristics of SLMed Ti6Al4Valloys was investigated.Based on the Johnson-Cook constitutive model of SLMed Ti6Al4Valloys,an orthogonal cutting model was developed to better understand the effect of physical-mechanical properties on the shear localization,which dominates the formation mechanism of serrated chips in post-machining of SLMed Ti6Al4V alloy.The results showed that the critical cutting speed(CCS)for chip serration of SLMed Ti6Al4V alloy is lower than that for serrated chips of conventional Ti6Al4V alloy,and the serrated profile of SLMed Ti6Al4V chips was more regular and pronounced.Besides,due to anisotropic microstructure and mechanical properties of SLMed Ti6Al4Valloys,the serration degree of chips produced on the top surfaces of SLMed Ti6Al4Valloys is more prominent than that of chips generated on the front surfaces.In addition,because of the poor deformation coordination and high plastic flow stresses of needle-like martensiteα′,the plastic flow and grain distortion in the adiabatic shear band(ASB)of SLMed Ti6Al4V chips are significantly smaller than those in the ASB of conventional Ti6Al4V with equiaxed grains.

Thermal decomposition kinetics of titanium hydride and Al alloy melt foaming process

A temperature programmed decomposition (TPD) apparatus with metal tube struc- ture, in which Ar is used as the carrier gas, is established and the TPD spectrum of titanium hy- dride is acquired. Using consulting table method (CTM), spectrum superposition method (SSM) and differential spectrum technique, TPD spectrum of titanium hydride is separated and a set of thermal decomposition kinetics equations are acquired. According to these equations, the rela- tionship between decomposition quantity and time for titanium hydride at the temperature of 940 K is obtained and the result well coincides with the Al alloy melt foaming process.

Micro-inhomogeneous structure of liquid Al-Fe alloys

Using X-ray diffraction, the structure factors of molten Al-Fe alloys were determined as a function of composition at a constant 1 550℃. The nearest neighbour distance and coordination number are given. Both structure factors and total density functions could be well reproduced by a micro-inhomogeneous model. The entire concentration region can be divided into four intervals with Al, Al7Fe, Al5Fe2,Fe3Al and Fe acting as borders. Alloys situated at the borders of the concentration intervals contain clusters of one type whose composition represents that of the alloy in question. The alloys between the borders contain clusters of the two border types.

Structures and electrochemical performances of as-spun RE-Mg-Ni-Co-Al alloys applied to Ni-MH battery

The La-Mg-Ni-Co-Al-based AB2-type La0.8-xCe0.2YxMgNi3.4Co0.4Al0.1 （x = 0, 0.05, 0.1, 0.15, 0.2） alloys were prepared by melt spinning. The effects of Y content on the structures and electrochemical hydrogen storage characters were thoroughly studied. The structures of the experimental samples were analyzed by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. It is shown that there are a main phase LaMgNi4 and a second phase LaNi5 in the experimental samples. The variation of Y content incurs obvious changes of the phase abundance without changing phase composition. Namely, with the increase of Y content, the LaMgNi4 phase increases and LaNi5 phase decreases. Furthermore, melt spinning and the replacement of Y for La also lead to the grains refinement of the alloy. The electrochemical tests display that the as-spun alloys possess excellent activation properties, and obtain the maximums of discharge capacity at the first cycling. The replacement of Y for La can visibly facilitate the discharge potential characteristics, however,diminish the discharge capacity. The electrochemical kinetics, involving in the high rate discharge ability （HRD）, hydrogen diffusion coefficient （D）, limiting current density （IL） and charge transfer rate, increases firstly and then decreases with the increase of Y content. The cyclic stability is greatly improved by melt spinning and the replacement of Y for La, which is derived from the improvement of the anti-corrosion, oxidation-resistance and the anti-pulverization abilities.

Mechanical Behaviors of Soft Elastomers Filled with LowMelting Alloys

Soft elastomers with mechanical properties similar to biological tissues have shown encouraging potential in applications of biomedical devices and stretchable electronics.With the ability to enhance electric and thermal conductivity,embedding low melting alloys into soft elastomer matrix has received considerable attention in recent years.However,the mechanical properties,especially the fatigue behaviors of these soft composites,have not been extensively investigated.Here,we fabricate two silicone elastomers filled with eutectic gallium-indium,a liquid metal alloy,which has a melting temperature around room temperature.The cyclic loading–unloading tests are first performed on the composites with low melting alloys in either solid or fluid state.The results show that the modulus and energy dissipation density of the composite increase with the ratio of the alloys when the deformation temperature is below the melting temperature,while these properties decrease with the ratio of alloys when they are in the fluid state.In contrast,the failure strain shows an opposite trend.Mechanical tests are further performed on specimens with a precut to measure the fracture energy and fatigue threshold.It is demonstrated that both fracture energy and fatigue threshold are significantly enhanced in the presence of low melting alloys regardless of their states.Finally,we apply a continuum damage model to describe the Mullins effect of the soft composites observed in the loading–unloading cycles,which further reveals the change of mechanical properties with deformation for different compositions of soft composites.