Solidification

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Kinds of Solidification

  • dendritic solidification
  • directional solidification
  • rapid solidification

  • Terms modified by Solidification

  • solidification problem
  • solidification process

  • Selected Abstracts


    Modeling of Hot Ductility During Solidification of Steel Grades in Continuous Casting , Part I,

    ADVANCED ENGINEERING MATERIALS, Issue 3 2010
    Dieter Senk
    The present paper gives an overview of the simultaneous research work carried out by RWTH Aachen University and ThyssenKrupp Steel Europe AG. With a combination of sophisticated simulation tools and experimental techniques it is possible to predict the relations between temperature distribution in the mould, solidification velocity, chemical steel composition and, furthermore, the mechanical properties of the steel shell. Simulation results as well as experimentally observed microstructure parameters are used as input data for hot tearing criteria. A critical choice of existing hot tearing criteria based on different approaches, like critical strain and critical strain rate, are applied and developed. The new "damage model" is going to replace a basic approach to determine hot cracking susceptibility in a mechanical FEM strand model for continuous slab casting of ThyssenKrupp Steel Europe AG. Critical strains for hot cracking in continuous casting were investigated by in situ tensile tests for four steel grades with carbon contents in the range of 0.036 and 0.76,wt%. Additionally to modeling, fractography of laboratory and industrial samples was carried out by SEM and EPMA and the results are discussed. [source]


    Modelling of Hot Ductility during Solidification of Steel Grades in Continuous Casting , Part II,

    ADVANCED ENGINEERING MATERIALS, Issue 3 2010
    Bernd Böttger
    In continuous casting, the probability of hot cracks developing strongly depends on the local solidification process and the microstructure formation. In ref. 1, an integrative model for hot cracking of the initial solid shell is developed. This paper focuses on solidification modelling, which plays an important role in the integrated approach. Solidification is simulated using a multiphase-field model, coupled online to thermodynamic and diffusion databases and using an integrated 1D temperature solver to describe the local temperature field. Less-complex microsegregation models are discussed for comparison. The results are compared to EDX results from strand samples of different steel grades. [source]


    Solidification of binary aqueous solution cooled from above

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2010
    Shigeo Kimura
    Abstract Freezing and melting phenomena are important in many different fields, including crystal growth, casting, metallurgy, geophysics, and oceanography. Solidification of a multi-component solution is the one often observed in nature. In order to investigate basic features of the freezing processes of binary systems, we conducted a series of laboratory experiments in a rectangular box cooled from above using aqueous NaNO3 solution. During the freezing, the solid phase always grows into many needle-like crystals called the mushy layer. We measured the growth of the mushy layer thickness, the solid fraction, the temperature, and the concentration distributions. The average solid fraction is found to increase with time in the mushy layer. This causes a slow descent of the released solute in the mushy layer and its eventual fall into the liquid region below because of gravity. We propose a one-dimensional model to explain the horizontally-averaged mushy layer growth. In the model, the estimate of a heat flux at the mushy-liquid interface due to natural convection is found essential for a correct prediction. The proposed theory predicts well the growth of the mushy-layer and the average solid fraction, once the convective heat flux is properly given. © 2009 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20278 [source]


    Solidification in heat packs: II.

    AICHE JOURNAL, Issue 2 2003
    Role of cavitation
    When the metallic trigger in a commercial heat pack is flexed to initiate solidification, the acceleration of the liquid near the solid surface can cause cavitation and collapse of small vapor bubbles. It is investigated whether such cavitation is responsible for the operation of the metallic trigger in the subcooled sodium acetate solution in a heat pack. Using cavity collapse theory and the results in Part I for the nucleation pressure of a sodium acetate solution, it is shown that cavitation can generate pressures greater than the nucleation pressure of the solution. However, the period of time during which the solution is exposed to such high pressure is not sufficient to lead to nucleation, and hence the metallic trigger does not induce solidification as a result of cavitation. Experimental results, using sonication, tribonucleation, and shock waves, confirm the theoretical findings. [source]


    Solidification in heat packs: III.

    AICHE JOURNAL, Issue 2 2003
    Metallic trigger
    The metallic trigger used in commercial heat packs initiates solidification by releasing minute crystals of solid sodium acetate trihydrate into the subcooled solution. These crystals are harbored in submicron cracks on the disk's surface and are released when the disk is flexed. Using scanning electron microscopy, such seed crystals are observed on the surface of a disk after flexing it. Classic nucleation theory is used to investigate the behavior of crystals residing in the cracks on the metallic disk's surface during heating and cooling. Sodium acetate trihydrate crystals are capable of surviving in a 1-nm crack or smaller at regeneration temperatures of the order of 353 K. These seed crystals grow to the mouth of the crack at temperatures below the liquidus, but can only promote solidification of the whole solution surrounding the disk at temperatures below 256 K or when the disk is flexed. [source]


    In Situ X-Ray Radiography and Tomography Observations of the Solidification of Aqueous Alumina Particle Suspensions,Part I: Initial Instants

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009
    Sylvain Deville
    This paper investigates by in situ high-resolution X-ray radiography and tomography the behavior of colloidal suspensions of alumina partic les during directional solidification by freezing. The combination of these techniques provided both qualitative and quantitative information about the propagation kinetic of the solid/liquid interface, the particle redistribution between the crystals and a particle-enriched phase, and the three-dimensional organization of the ice crystals. In this first part of two companion papers, the precursor phenomena leading to directional crystallization during the first instants of solidification are studied. Mullins,Sekerka instabilities are not necessary to explain the dynamic evolution of the interface pattern. Particle redistribution during these first instants is dependent on the type of crystals growing into the suspension. The insights gained into the mechanisms of solidification of colloidal suspensions may be valuable for the materials processing routes derived for this type of directional solidification (freeze-casting), and of general interest for those interested in the interactions between solidification fronts and inert particles. [source]


    Particle Redistribution During Dendritic Solidification of Particle Suspensions

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2006
    Noah O. Shanti
    Solidification of the liquid medium in ceramic suspensions containing less than a critical volume fraction powder leads to the formation of particle-free dendrites of the frozen medium. These particle-free dendrites create, after sublimation of the frozen vehicle, large dendrite pores. We define the conditions under which particle-free dendrites form, and relate the size and volume fraction of the dendrites to the volume fraction powder and the solidification rate. [source]


    Performance of thin-film transistors fabricated by sequential lateral solidification crystallization techniques

    PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 12 2008
    M. A. Exarchos
    Abstract The performance of Excimer Laser Annealed (ELA) Thin-Film Transistors (TFTs), in terms of drain current behaviour in unstressed as well as in DC stressed devices, is presented. The transistors studied were fabricated under different irradiation schemes of a novel Sequential Lateral Solidification (SLS) process. As far as unstressed transistors concerned, drain current transients relaxed through stretched exponential law. Fitting results disclosed that both gate dielectric polarization and carrier recombination mechanisms occurred through transient relaxation. Deep Level Transient Spectroscopy (DLTS) technique was called forth in order to investi- gate the origin of carrier recombination mechanisms. DC hot carrier stress measurements, under "worst ageing condition" regime, were conducted in order to probe degradation mechanisms and device reliability standards. Crystal domain size significantly affects threshold voltage degradation. The latter increases with decreasing crystal domain size, due to increased concentration of protrusions in the polysilicon film. Transconductance degradation also depends on crystal domain size, attributed mainly to bulk polysilicon trap generation. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Isotactic polypropylene solidification under pressure and high cooling rates.

    POLYMER ENGINEERING & SCIENCE, Issue 11 2000
    A master curve approach
    Solidification in industrial processes very often involves flow fields, high thermal gradients and high pressures: the development of a model able to describe the polymer behavior becomes complex. Recently a new equipment has been developed and improved to study the crystallization of polymers when quenched under pressure. An experimental apparatus based on a modified, special injection moulding machine has been employed. Polymer samples can be cooled at a known cooling rate up to 100°C/s and under a constant pressure up to 40 MPa. Density, Micro Hardness (MH), Wide angle X-ray diffraction (WAXD), and annealing measurements were then used to characterize the obtained sample morphology. Results on one iPP sample display a lower density and a lower density dependence on cooling rate for increasing pressure. Micro hardness confirms the same trend. A deconvolution technique of WAXD patterns is used to evaluate the final phase content of samples and to assess a crystallization kinetics behavior. A master curve approach to explain iPP behavior under pressure and high cooling rates was successfully applied on density results. On the basis of this simple model it is possible to predict the final polymer density by superposition of the effect of cooling rate and the effect of pressure in a wide range of experimental conditions. [source]


    Morphology in Immiscible Polymer Blends During Solidification of an Amorphous Dispersed Phase under Shearing

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2002
    Yves Deyrail
    Abstract Solidification under shear of dispersed polycarbonate (PC) fibers in copolymer polyethylene-methyl acrylate matrix (EMA) was investigated using a hot optical shear device. First, the deformation of PC droplets and its modeling under isothermal conditions were studied for comprehension purposes. Overall agreement with literature models was found and the main influence of the viscosity ratio has been stressed. Second, the morphology control through dynamic quenching was experimented. It consists of solidifying the amorphous PC dispersed phase under shear flow. Break-up times of PC fibers were taken into account. Shear rate and quenching-time balance was demonstrated. Thus, during dynamic solidification, a fibrillar morphology could be obtained through rapid quenching. Long quenching times allow nodular morphology, whose size depends on the shear rate used. PC rods can be obtained by adjusting the shear rate during dynamic quenching. La solidification sous cisaillement du polycarbonate (PC) dispersé dans une matrice copolymère éthylène-acétate de vinyle (EMA) a été suivie à l'aide d'un microscope et d'une platine de cisaillement chauffante. Dans un premier temps la déformation isotherme de billes de PC pour différentes températures a été étudiée, ainsi que sa modélisation. Une bonne corrélation avec les modèles issus de la littérature a été obtenue. L'importance du rapport des viscosités a été ainsi soulignée. Dans un second temps le contrôle de la morphologie par le procédé de « refroidissement dynamique » a été expérimenté. Celui-ci consiste à solidifier le PC sous cisaillement pendant le refroidissement. Les temps de rupture des fibres de PC ont été considérés et l'importance du couple gradient de cisaillement-temps de refroidissement sur le contrôle de la morphologie a été mis en évidence. Pendant la solidification, un refroidissement rapide permet d'obtenir une morphologie fibrillaire. [source]


    In-situ TiC precipitation in molten Fe-C and their characterisation

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2008
    K. I. Parashivamurthy
    Abstract TiC particles were formed in liquid iron solution by the reaction between pure titanium and carbon available in molten iron. TiC particles have been precipitated in steels with four different carbon contents by in situ reactions during melting. The influence of titanium and carbon concentration on the precipitation of TiC was studied. The samples were studied by means of optical microscopy, scanning electron microscopy and X-ray microanalysis. The morphology of the obtained crystals was studied and correlated with carbon and titanium. It was found that TiC crystallises as primary crystals at 1600°C during solidification of the Fe-Ti-C melt. The obtained crystals were of cubic, rectangle and had maximum size of 18.7 µm. The size and shape of the carbides increases with increasing carbon and titanium in molten iron. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Contribution to the stability analysis of the dewetted Bridgman growth under microgravity conditions

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 6 2004
    L. Bizet
    Abstract Experimental observations show that the gap between the sample and the crucible, commonly obtained after solidification in microgravity, is remarkably stable. With the aim to understand the reason of this stability, the dewetting phenomenon is studied by Lyapunov's method. After a short review of the existing mechanisms leading to dewetting, the open smooth crucible configuration is chosen as the most representative. The analytical stability analysis, taking into account geometrical and thermal effects, performed under some boundary heat transfer approximations, shows that, in most cases, the dewetting process is intrinsically stable. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Microstructural Analysis of the Reinforced Al-Cu5mgti/Tib2 5,wt % Alloy for Investment Casting Applications,

    ADVANCED ENGINEERING MATERIALS, Issue 6 2010
    Pedro Egizabal
    Abstract The paper describes the influence of 5,wt % titanium diboride (TiB2) particles on the microstructure of an Al-Cu alloy produced by plaster casting process. The elaboration route leads to a composite material with 1% of in situ TiB2 particles and 4% ex situ of TiB2 particles. The comparison of the reinforced alloy with the corresponding non-reinforced counterpart makes clear that the presence of TiB2 particles has a large influence in the observed microstructure. The presence of TiB2 particles decreases the grain sizes and the porosity level. It is also found that TiB2 particles play an important role in the precipitation events of Al2Cu precipitates that are formed during solidification at the TiB2/aluminum matrix interfaces. [source]


    Modeling of Coating Process, Phase Changes, and Damage of Plasma Sprayed Thermal Barrier Coatings on Ni-Base Superalloys,

    ADVANCED ENGINEERING MATERIALS, Issue 3 2010
    Tilmann Beck
    The paper gives an overview on the modeling activities on plasma sprayed thermal barrier coating in the frame of TFB 63. In the first part, through-process modeling of the APS deposition of a ZrO2 based TBC is described. Starting from simulation of the plasma jet, heat transfer into the powder particles, particle melting, particle impact on the substrate surface, and solidification is simulated. A homogenization method is introduced to describe the mechanical properties of the resulting TBC. The second part shows simulation of interdiffusion and phase transformations of MCrAlY and intermetallic oxidation protection coatings on several cast Ni-base alloy substrates. Finally, FEM-based damage simulation of oxidation protection coatings by transversal fatigue cracks during thermomechanical fatigue loading as well as by delamination of the TBC during thermocyclic loading is discussed. [source]


    Modeling the Porosity Formation in Austenitic SGI Castings by Using a Physics-Based Material Model,

    ADVANCED ENGINEERING MATERIALS, Issue 3 2010
    B. Pustal
    Abstract On solidification, microsegregations build up in solid phases due to changes in solid concentrations with temperature. Diffusion, which is a kinetic process, usually reduces the occurrence of microsegregations. This work is aimed at modeling such kinetic effects on the solidification of austenitic cast iron, using a holistic approach. For this purpose, a microsegregation model is developed and validated. Moreover, this model is directly coupled to a commercial process-simulation tool and thermodynamic software. A series of GJSA-XNiCr 20-2 clamp-rings is cast by varying the inoculation state and the number of feeders. The composition of this cast alloy is analyzed and the microstructure characterized to provide input data for the microsegregation model. In order to validate the software, cooling curves are recorded; differential thermal analysis, electron dispersive X-ray analysis and electron probe micro analysis are carried out. Furthermore, the porosity within the casting is analyzed by X-ray. By performing coupled simulations, the different cooling characteristics within the casting lead to pronounced differences in phase fractions and solidification temperatures which are due to dendrite arm coarsening. The hot spot effect below the feeders is assisted by a shift towards lower solidification temperatures over the solidification time. This shift is a result of the local cooling characteristics, which can only be predicted when process simulation is directly coupled with material simulation. The porosity predictions and the porosity analysis exhibit good agreement. A comparison between experimental and virtual cooling curves closes, implying that the novel coupling concept and its implementation are valid. [source]


    Heat Transport in Closed Cell Aluminum Foams: Application Notes,

    ADVANCED ENGINEERING MATERIALS, Issue 10 2009
    Jaime Lázaro
    Heat transport equations have been used to solve, by implementing the Finite Element Method (FEM), three different cases representative of the aluminium foams life: the production process (solidification in the molten state), post-production (water quenching heat treatments) and applications (fire barriers). [source]


    Effects of Zirconium Additions on the Microstructure of As-Cast and Aged AZ91 Magnesium Alloy

    ADVANCED ENGINEERING MATERIALS, Issue 3 2009
    Farhoud Kabirian
    The effects of Zr addition on the microstructure of AZ91 alloy were investigated under as-cast and isothermally aged conditions. The microstructures contained a eutectic , -Mg17Al12 phase together with fine Al,Zr intermetallic compounds. These intermetallic compounds inhibited grain growth during the 420,°C isothermal aging of Zr-containing alloys. Microstructural changes caused by Zr additions were most probably due to the consumption of Al by Zr, and redistribution of Al during solidification of dendrites. [source]


    Surface Tension and Viscosity of the Ni-based Superalloy CMSX-4 Measured by the Oscillating Drop Method in Parabolic Flight Experiments,

    ADVANCED ENGINEERING MATERIALS, Issue 5 2007
    K. Higuchi
    The surface tension and the viscosity of the Ni-based superalloy CMSX-4 were measured by the oscillating drop method on electromagnetically levitated specimen under reduced gravity conditions on a parabolic flight. The twenty seconds of reduced gravity available in a single parabola proved sufficient for melting, heating into the stable liquid and free cooling to solidification. [source]


    Nanocrystallized Al92Sm8 Amorphous Alloy Investigated by High-Resolution Microscopy and 3D Atom-Probe Analysis

    ADVANCED ENGINEERING MATERIALS, Issue 3 2007
    T. Gloriant
    A partially nanocrystallized amorphous Al92Sm8 (at.%) alloy was obtained directly by rapid solidification (one-step method). Because of the significant retained plasticity of the as-quenched alloy, the nanostructure and the atomic species distribution within the nanocomposite material could be characterized by field-ion microscopy (FIM) and by three-dimensional atom-probe analysis (3DAP). [source]


    The Joint Research Program "CPR Precipitation" , Towards More Powerful Computer Assisted Metallurgy Codes,

    ADVANCED ENGINEERING MATERIALS, Issue 12 2006
    P. Maugis
    Computer Assisted Metallurgy (CAM) is developed and used by both Alcan and Arcelor to predict material properties, optimize processing and accelerate the development of new innovative solutions. These CAM codes describe the microstructure evolution of an alloy from solidification to the final step of the transformation schedule and predict usage properties from the simulated end product microstructure. The accuracy of the predictions requires a reliable laboratory or plant experimental database and robust physical laws. [source]


    Biocompatibility of Lotus-type Stainless Steel and Titanium in Alveolar Bone

    ADVANCED ENGINEERING MATERIALS, Issue 9 2006
    Y. Higuchi
    Abstract Lotus-type porous stainless steel (SUS304L) and porous titanium were fabricated by unidirectional solidification in a mixture gas of hydrogen and argon. The porous metals which were cut into 5,mm cubes (non-dehydrogenated) and 3.4,mm,,×,5,mm cylinders (dehydrogenated) were implanted into the canine mandible alveolar bone for two, four and eight weeks for animal experiments. The changes in the tissues were observed using SEM. For porous stainless steel (cylindrical; dehydrogenated) new formation of bones was observed around the sample in two weeks without any sign of bony ingrowth into the pores. The osteogenesis was found in shallow areas in the pores in four weeks and deep in the pores in eight weeks. Porous titanium, on the other hand, showed deep ingrowth of new bones in four weeks. Our observations allowed us to expect application of the porous metals as biomaterials. They maintain mechanical strength and are lighter in weight so that it is expected to be applied for dental implants and core materials of artificial bones. [source]


    Metamaterials: How Far Are We from Making Metamaterials by Self-Organization?

    ADVANCED FUNCTIONAL MATERIALS, Issue 7 2010
    The Microstructure of Highly Anisotropic Particles with an SRR-Like Geometry (Adv. Funct.
    As part of ongoing efforts to create metamaterials by engineered self-organization using solidification of eutectics, D. A. Pawlak et al. report on page 1116 the fabrication of a fractal material with split-tubes mimicking (in cross section) the famous split-ring resonators (SRRs). The latter, when made of metal, are the basic element of a structure showing negative refractive index. This article shows that metallo-dielectric structures can be fabricated. The method employed has high potential for manufacturing materials with various functionalities. [source]


    How Far Are We from Making Metamaterials by Self-Organization?

    ADVANCED FUNCTIONAL MATERIALS, Issue 7 2010
    The Microstructure of Highly Anisotropic Particles with an SRR-Like Geometry
    Abstract Metamaterials offer new unusual electromagnetic properties, which have already been demonstrated, and many postulated new functionalities are yet to be realized. Currently, however, metamaterials are mostly limited by narrow band behavior, high losses, and limitation in making genuinely 3D materials. In order to overcome these problems an overlap between metamaterial concepts and materials science is necessary. Engineered self-organization is presented as a future approach to metamaterial manufacturing. Using directional solidification of eutectics, the first experimental realization of self-organized particles with a split-ring resonator-like cross section is demonstrated. This unusual morphology/microstructure of the eutectic composite has a fractal character. With the use of TEM and XRD the clear influence of the atomic crystal arrangement on the microstructure geometry is presented. The materials obtained present very high anisotropy and can be obtained in large pieces. Metallodielectric structures can be created by etching and filling the space with metal. The next steps in the development of self-organized materials exhibiting unusual properties are discussed. [source]


    Analysis of Nanostructuring in High Figure-of-Merit Ag1,xPbmSbTe2+m Thermoelectric Materials

    ADVANCED FUNCTIONAL MATERIALS, Issue 8 2009
    Bruce A. Cook
    Abstract Thermoelectric materials based on quaternary compounds Ag1,xPbmSbTe2+m exhibit high dimensionless figure-of-merit values, ranging from 1.5 to 1.7 at 700,K. The primary factor contributing to the high figure of merit is a low lattice thermal conductivity, achieved through nanostructuring during melt solidification. As a consequence of nucleation and growth of a second phase, coherent nanoscale inclusions form throughout the material, which are believed to result in scattering of acoustic phonons while causing only minimal scattering of charge carriers. Here, characterization of the nanosized inclusions in Ag0.53Pb18Sb1.2Te20 that shows a strong tendency for crystallographic orientation along the {001} planes, with a high degree of lattice strain at the interface, consistent with a coherent interfacial boundary is reported. The inclusions are enriched in Ag relative to the matrix, and seem to adopt a cubic, 96 atom per unit cell Ag2Te phase based on the Ti2Ni type structure. In-situ high-temperature synchrotron radiation diffraction studies indicated that the inclusions remain thermally stable to at least 800,K. [source]


    Effect of micro mass transfer through phase interface on numerical simulation of solidification process

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 6 2004
    Yanhui Feng
    Abstract Existing models for the solute redistribution during solidification have been reviewed. Some typical models are applied for the numerical simulation of heat and mass transfer with phase change under experimental condition of inverse casting. The results show that the effect of micro mass transfer models on the formation of the new phase cannot be omitted. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(6): 393,401, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20024 [source]


    Analysis of stress due to shrinkage in a hardening process of liquid epoxy resin

    HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 3 2002
    Tetsuro Nishimura
    Abstract At present, epoxy resin is applied during the manufacturing of more compact and thinner components for the packaging of electronic and other devices. Epoxy resin has superior properties in terms of heat resistance, insulation, and strength; however, defects such as deformations and cracks often occur because of stress concentration. It is important to determine the inner stress of resin solidification for molding processes. Through a combination of numerical analyses of heat generated due to chemical reactions and experiments on shrinkage and strain that occur during hardening of epoxy resin, it becomes possible to analyze the stress generated due to hardening shrinkage. The developed analytical method can contribute to the realization of highly reliable components made of epoxy resin. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(3): 194,211, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10028 [source]


    Processing of Bulk Metallic Glass

    ADVANCED MATERIALS, Issue 14 2010
    Jan Schroers
    Abstract Bulk metallic glass (BMG) formers are multicomponent alloys that vitrify with remarkable ease during solidification. Technological interest in these materials has been generated by their unique properties, which often surpass those of conventional structural materials. The metastable nature of BMGs, however, has imposed a barrier to broad commercial adoption, particularly where the processing requirements of these alloys conflict with conventional metal processing methods. Research on the crystallization of BMG formers has uncovered novel thermoplastic forming (TPF)-based processing opportunities. Unique among metal processing methods, TPF utilizes the dramatic softening exhibited by a BMG as it approaches its glass-transition temperature and decouples the rapid cooling required to form a glass from the forming step. This article reviews crystallization processes in BMG former and summarizes and compares TPF-based processing methods. Finally, an assessment of scientific and technological advancements required for broader commercial utilization of BMGs will be made. [source]


    The Contemporary Professoriate: Towards a Diversified or Segmented Profession?

    HIGHER EDUCATION QUARTERLY, Issue 2 2007
    Nelly P. Stromquist
    On the empirical basis of six national studies (Mexico, Brazil, Peru, Denmark, Russia and South Africa), this paper examines the phenomenon of segmentation, defined as the solidification of deep hierarchies with little crossover between categories of institutions or individuals. The massification of higher education has brought about a great diversity of institutions and, concomitantly, stark differences among the professoriate. While the public sector has to some extent been able to protect its academic personnel, the for-profit sector is moving towards an unstable professoriate, poorly paid, hired mostly on a per-hour basis, and for whom sharing in academic governance is a distant dream. Some of this differentiation is emerging also within institutions and a new kind of academic who could be termed ,just-in-time knowledge worker' is on the rise. [source]


    Approximation to the interface velocity in phase change front tracking

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 2 2002
    P. H. Zhao
    Abstract Numerical models for front tracking in the sharp interface limit must calculate the interface velocity by means of a differentiation of the temperature field on both sides of the interface, the resulting velocity shows an oscillatory error that introduces noise in the solution. In unstable solidification problems, the noise can actually change the resulting solution. In this work, we look at the effect of the noise in the solution of dendritic solidification in an undercooled melt and analyse ways to control it. We conclude that at this point, we cannot suppress the noise and that methods to reduce it can actually lead to different solutions to the same problem. Copyright © 2001 John Wiley & Sons, Ltd. [source]


    Interface tracking finite volume method for complex solid,fluid interactions on fixed meshes

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 2 2002
    H. S. Udaykumar
    Abstract We present a numerical technique for computing flowfields around moving solid boundaries immersed in fixed meshes. The mixed Eulerian,Lagrangian framework treats the immersed boundaries as sharp solid,fluid interfaces and a conservative finite volume formulation allows boundary conditions at the moving surfaces to be exactly applied. A semi-implicit second-order accurate spatial and temporal discretization is employed with a fractional-step scheme for solving the flow equations. A multigrid accelerator for the pressure Poisson equations has been developed to apply in the presence of multiple embedded solid regions on the mesh. We present applications of the method to two types of problems: (a) solidification in the presence of flows and particles, (b) fluid,structure interactions in flow control. In both these problems, the sharp interface method presents advantages by being able to track arbitrary interface motions, while capturing the full viscous, unsteady dynamics. Copyright © 2001 John Wiley & Sons, Ltd. [source]