No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
An experimental study of deformation of a columnar dendritic mushy zone using a transparent succinonitrile-acetone alloy
Abstract
The deformation of a directionally solidified columnar dendritic mushy zone in a transparent succinonitrile-acetone (SCN-ACE)
alloy has been studied expermentally. In addition to solidifying dendritically like a metal alloy, this alloy also has mechanical
properties that are similar to those of metals near the melting point. The experiments are relevant, for example, to the deformation
of a partially solidified strand during continuous casting of steel slabs. A test cell was designed which allows for directional
solidification of the alloy and controlled compression of the solid-liquid mush which forms. Measurements during solidification
and deformation include temperatures, interface positions, local displacements of the solid skeleton in the mush, and liquid
concentrations. Results are presented for a range of initial test-cell thicknesses, deformation amounts, and deformation start
times. The measurements are suitable for validation of future models.
... The role of microstructures in initiating such defects, particularly the role of shear banding and dilation of the inter-granular spacing was not understood. Therefore, semi-solid deformation of partially molten alloys has been investigated by several researchers to explore the following key aspects: (i) microstructural response to deformation (e.g., [111]); (ii) granular behaviour of the semi-solid mixture, including Reynold's dilatancy (e.g., Gourlay and Dahle [34]); (iii) deformation of the microstructures such as equiaxed [61], columnar [112], and globular [22,113] morphologies; and (iv) the role of deformation on defects such as hottearing or hot-cracking (e.g., [52,114]), intermetallics [33] and porosity [29]. ...
... The role of microstructures in initiating such defects, particularly the role of shear banding and dilation of the inter-granular spacing was not understood. Therefore, semi-solid deformation of partially molten alloys has been investigated by several researchers to explore the following key aspects: (i) microstructural response to deformation (e.g., [111]); (ii) granular behaviour of the semi-solid mixture, including Reynold's dilatancy (e.g., Gourlay and Dahle [34]); (iii) deformation of the microstructures such as equiaxed [61], columnar [112], and globular [22,113] morphologies; and (iv) the role of deformation on defects such as hot-tearing or hot-cracking (e.g., [52,114]), intermetallics [33] and porosity [29]. ...
In this review, we present an overview of significant developments in the field of in situ and operando (ISO) X-ray imaging of solidification processes. The objective of this review is to emphasize the key challenges in developing and performing in situ X-ray imaging of solidification processes, as well as to highlight important contributions that have significantly advanced the understanding of various mechanisms pertaining to microstructural evolution, defects, and semi-solid deformation of metallic alloy systems. Likewise, some of the process modifications such as electromagnetic and ultrasound melt treatments have also been described. Finally, a discussion on the recent breakthroughs in the emerging technology of additive manufacturing, and the challenges thereof, are presented.
... Acetone was of particular interest to form an SCN alloy that preserved the linear solid-liquidus line in the SCN phase diagram. SCN has continued to be popular in solidification research as researchers continue to focus on more specific areas of solidification and grain refinement [47][48][49]. It has also garnered interests in electronics due to its solid conductive properties [50]. ...
Turbulent filling of molten metal in sand-casting leads to bi-films, porosity and oxide inclusions which results in poor mechanical properties and high scrap rate of sand castings. Hence, it is critical to understand the metal flow in sand-molds, i.e., casting hydrodynamics to eliminate casting defects. While multiple numerical methods have been applied to simulate this phenomenon for decades, harsh foundry environments and expensive x-ray equipment have limited experimental approaches to accurately visualize metal flow in sand molds. In this paper, a novel approach to solve this challenge is proposed using Succinonitrile (SCN) as a more accurate metal analog in place of water. SCN has a long history in solidification research due to its BCC (Body-Centered-Cubic) crystal structure and dendrite-like solidification (melting temperature ~60 °C) like molten aluminum. However, this is the first reported study on applying SCN through novel casting hydrodynamics to accurately visualize melt flow for casting studies. This paper used numerical simulations and experiments using both water and SCN to identify the critical dimensionless numbers to perform accurate metal flow analog testing. Froude’s number and wall roughness were identified as critical variables. Experimental results show that SCN flow testing was more accurate in recreating the flow profile of molten aluminum, thus validating its utility as a metal analog for metal flow research. Findings from this study can be used in future metal flow analysis such as: runner, in-gate and integrated filling-feeding-solidification studies.
... Industrial experiment, [5,6] of course, reveals in a full scale the relationship between the processing parameters and actual solidified structure of slabs, but this method is often prohibitively expensive or physically impossible. Physical simulation has sometimes been adopted using transparent materials [7] or metals with low melting points to study flow fields, [8,9] and solidification behav- iors. [10][11][12]This is the method that has most commonly been used to develop current solidification theories, [2] and it has contributed considerably to the study of flow fields in mold during continuous casting (CC). ...
Eighty years after the invention of continuous cast of steels, reproducibility from few mm3 samples in the laboratory to m3 product in plants is still a challenge. We have engineered a thermal simulation method to simulate the continuous casting process. The temperature gradient (G
L
) and dendritic growth rate (v) of the slab were reproduced by controlling temperature and cooling intensity at hot and chill end, respectively, in our simulation samples. To verify that our samples can simulate the cast slab in continuous casting process, the heat transfer, solidification structure, and macrosegregation of the simulating sample were compared to those of a much larger continuous casting slab. The morphology of solid/liquid interface, solidified shell thickness, and dendritic growth rate were also investigated by in situ quenching the solidifying sample. Shell thickness (δ) determined by our quenching experiment was related to solidification time (τ) by equation: δ = 4.27 × τ
0.38. The results indicated that our method closely simulated the solidification process of continuous casting.
... In solidification processing, deformation in the semisolid can induce a range of defects, including extrusion segregation in squeeze-casting [1] and surface exudation in direct-chill casting [7]. Although several prior investigations have identified deformation-driven melt flow as a possible mechanism of such defects [1,7,12], the influence of stress on a semi-solid alloy and the melt flow through the equiaxed microstructure are not clearly understood. Many models have been developed to predict the formation of those defects, based on the proposition of the mushy zone as a sponge saturated with liquid [2,7,13,14]. ...
The rheology of semi-solid alloys has been studied by a novel in situ tomographic technique. Via extruding an equiaxed Al-15 wt.%Cu alloy, the inhomogeneous coherent compression of the α-Al grains was quantified, including the interdendritic channel closure and formation of a liquid extrudate. This investigation not only provides important insights into the microstructural changes occurring during semi-solid deformation, but also offers a validation benchmark for segregation and rheological models. © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
... [16,17] The current authors support the hypothesis that most deformation in the mushy zone occurs near the strand core, where the solid volume fraction is the lowest rather than a homogeneous deformation across the whole section of the mushy zone. This opinion has been supported by many experimental studies [29][30][31] ; however difficulties in determining the empirical constants in Eq. [17] remain. Another issue is the volume change of the solid-state phase transition (from d ferrite to c austenite), which may play an important role in the mechanical deformation as well. ...
A two-phase columnar solidification model is used to study the principle of mechanical soft reduction (MSR) for the reduction of centerline segregation in slab casting. The two phases treated in the model are the bulk/interdendritic melt and the columnar dendrite trunk. The morphology of the columnar dendrite trunk is simplified as stepwise growing cylinders, with growth kinetics governed by the solute diffusion in the interdendritic melt around the growing cylindrical columnar trunk. The solidifying strand shell moves with a predefined velocity and the shell deforms as a result of bulging and MSR. The motion and deformation of the columnar trunks in response to bulging and MSR is modeled following the work of Miyazawa and Schwerdtfeger from the 1980s. Melt flow, driven by feeding of solidification shrinkage and by deformation of the strand shell and columnar trunks, as well as the induced macrosegregation are solved in the Eulerian frame of reference. A benchmark slab casting (9-m long, 0.215-m thick) of plain carbon steel is simulated. The MSR parameters influencing the centerline segregation are studied to gain a better understanding of the MSR process. Two mechanisms in MSR modify the centerline segregation in a slab casting: one establishes a favorable interdendritic flow field, whereas the other creates a non-divergence-free deformation of the solid dendritic skeleton in the mushy region. The MSR efficiency depends not only on the reduction amount in the slab thickness direction but also strongly on the deformation behavior in the longitudinal (casting) direction. With enhanced computation power the current model can be applied for a parameter study on the MSR efficiency of realistic continuous casting processes.
... Techniques using transparent plastic crystal systems, which solidify dendritically in a manner similar to Ni-base superalloys, have opened a literal window into the growth mechanisms of dendritic structures. [69,70,72,[86][87][88][89] Unfortunately, theory is still struggling to describe what is observed in complex, multicomponent systems. Additionally, the controlled laboratory experiments that are often used as inspiration or qualification for dendrite growth models are not typically representative of the complex conditions occurring during solidification of a turbine blade with three-dimensional shape. ...
The drive for higher efficiency in very large industrial gas turbines (IGTs) used in power generation applications has led to the need for directional solidification of large cross-section components, such as turbine blades, used in the hot gas path sections of the IGTs. The Bridgman directional solidification technique, which is currently used to produce these components, has been optimized for much smaller aero-engine components. The scale-up of this technique to produce large parts has resulted in numerous problems, and consequently low casting yield, which can all be related to the limited cooling capability of the Bridgman process. In this dissertation, a higher cooling efficiency process, liquid-metal cooling (LMC) using Sn as the cooling medium, has been evaluated for improved capability to cast large cross-section components. A series of castings were made for direct comparison using both the conventional Bridgman and the high thermal gradient LMC processes. Casting conditions were selected to simulate the state of the art for the Bridgman method and to assess the limits of casting with the less familiar LMC method. The experiments were evaluated through thermocouple analyses of casting conditions and post-casting analyses of grain defects, microstructural features, and mechanical behavior. Additionally, a finite element model of the solidification process was developed to further elucidate casting conditions. The casting parameters and elements of the LMC process that had the greatest influence on casting conditions were determined. Results indicated that the LMC process is capable of significantly enhancing cooling efficiency during directional solidification of large cross-section components. The enhanced cooling allowed much faster solidification withdrawal rates and resulted in substantially refined cast microstructure. The LMC process eliminated freckle-type defects in all cases and considerably reduced other casting defects under optimal conditions. It also was determined that the location of the solidification front during the LMC process is a crucial parameter that must be controlled to produce a high quality casting. Additionally, a floating thermal baffle used with the LMC-Sn process was established as an indispensable element of the LMC process.
A multi-physics model has been developed to investigate the molybdenum and nickel distribution in large-scale Ti-0.3 wt.% Mo-0.8 wt.% Ni slab ingots obtained by electron beam cold hearth melting. Numerical methods are pivotal in revealing the distribution trends of molybdenum and nickel in slab ingot in different casting conditions. The distribution of molybdenum slightly changed between 0.28 and 0.32 wt.% in the solidified ingot. However, the sharp change in the nickel distribution (between 0.73 and 1.53 wt.%) was caused by the fluid velocity decrease along the flow direction, resulting from a weakened vortexing effect. Additionally, the increase of the casting speed or pouring temperature led to a deeper molten pool and evident vortexing effect. A potential relationship indicates the decrease of nickel segregation degree at higher pouring temperatures, or the casting speed decrease within the research scope.
Two mononuclear mixed-ligand ruthenium(III) complexes with oxalate dianion (ox2−) and acetylacetonate ion (2,4-pentanedionate, acac−), K2[Ru(ox)2(acac)] (1) and K[Ru(ox)(acac)2] (2), were prepared as a candidate for a building block. In fact, reaction of complex 2 with manganese(II) sulfate gave a heterometallic tetranuclear complex, TBA[MnII{(μ-ox)RuIII(acac)2}3] (5) in the presence of tetrabutylammonium (TBA) bromide. The 1H NMR, UV–Vis, selected IR and FAB mass spectral data of these complexes are presented. Both mixed-ligand ruthenium(III) complexes gave a Nernstian one-electron reduction step in 0.1 mol dm−3 Na2SO4 aqueous solution on a mercury electrode at 25 °C. Comparison of observed reversible half-wave potentials with calculated values for a series of [Ru(ox)n(acac)3−n]n− (n=0–3) complexes by using Lever’s ligand electrochemical parameters is presented.
Hot tearing susceptibility of two Ni-base superalloys, IN792 and CM247, during directional solidification was studied. Effects Hot tearing susceptibility of two Ni-base superalloys, IN792 and CM247, during directional solidification was studied. Effects
of grain-boundary (GB) misorientation on castability were examined by casting single-crystal (SC) and bicrystal (BC) specimens. of grain-boundary (GB) misorientation on castability were examined by casting single-crystal (SC) and bicrystal (BC) specimens.
Crack-free specimens were obtained in castings with GB misorientation angles of less than ∼12 deg. Severe cracking occurred Crack-free specimens were obtained in castings with GB misorientation angles of less than ∼12 deg. Severe cracking occurred
if the GB angle was greater than 25 deg. Secondary dendrite arm length right at the GB was found to be larger than in the if the GB angle was greater than 25 deg. Secondary dendrite arm length right at the GB was found to be larger than in the
GB vicinity and to increase with GB misorientation. The amount of eutectic melt and foreign element segregation is also larger GB vicinity and to increase with GB misorientation. The amount of eutectic melt and foreign element segregation is also larger
at the GB. The greater susceptibility of the GB to hot tearing is almost certainly caused by reduced strength compared to at the GB. The greater susceptibility of the GB to hot tearing is almost certainly caused by reduced strength compared to
the grain interior. The reduced strength is either due to reduced secondary arm bridging because of geometrical constraints the grain interior. The reduced strength is either due to reduced secondary arm bridging because of geometrical constraints
or due to the existence of a thin liquid film as a result of stronger segregation. or due to the existence of a thin liquid film as a result of stronger segregation.
A two-phase volume-averaged continuum model is presented that quantifies macrosegregation formation during solidification
of metallic alloys caused by deformation of the dendritic network and associated melt flow in the coherent part of the mushy
zone. Also, the macrosegregation formation associated with the solidification shrinkage (inverse segregation) is taken into
account. Based on experimental evidence established elsewhere, volumetric viscoplastic deformation (densification/dilatation)
of the coherent dendritic network is included in the model. While the thermomechanical model previously outlined (M. M’Hamdi,
A. Mo, and C.L. Martin: Metall. Mater. Trans. A, 2002, vol. 33A, pp. 2081–93) has been used to calculate the temperature and velocity fields associated with the thermally
induced deformations and shrinkage driven melt flow, the solute conservation equation including both the liquid and a solid
volume-averaged velocity is solved in the present study. In modeling examples, the macrosegregation formation caused by mechanically
imposed as well as by thermally induced deformations has been calculated. The modeling results for an Al-4 wt pct Cu alloy
indicate that even quite small volumetric strains (≈2 pct), which can be associated with thermally induced deformations, can
lead to a macroscopic composition variation in the final casting comparable to that resulting from the solidification shrinkage
induced melt flow. These results can be explained by the relatively large volumetric viscoplastic deformation in the coherent mush resulting from the applied constitutive model, as well as the relatively large
difference in composition for the studied Al-Cu alloy in the solid and liquid phases at high solid fractions at which the
deformation takes place.
Glass samples with composition of (64-x)TeO2 + (x)ZnO + 15 ZnCl2 + 0.5 Sm2O3 + 0.5
Er2O3 (x = 20, 25 and 30 mol%) are prepared by melt quenching method. The season for co-doping
with rare earth ions such as samarium (Sm3+) and erbium (Er3+) is to explore the feasibility of their
simultaneous exploitation as high performing up-converted lasing materials. The role of varying
modifier of ZnO concentration in improving the hardness and structural properties are evaluated.
The density is observed to reduce and ionic packing density is augmented with increasing
concentration of ZnO. Glass with 25 mol% of ZnO revealed the optimum hardness of 2830 N/mm2
.
Incorporation of Zn2+ into the tellurite host matrix is found to shift the IR bands position slightly
without altering their intensity. Bonding vibrations corresponding to bending of TeO3 unit
(784-762 cm-1), stretching of TeO4 units (678-676 cm-1) and Zn-O bonds (462-452 cm-1) are
evidenced. Incorporation of ZnO as modifier is established to enhance the hardness and improved
the structural properties. The proposed glass composition may be useful for industrial purposes.
Three dimensional deformation behavior of continuously cast strand during soft reduction, which is considered to be an important factor when applying optimum reduction rate in soft reduction technology for reducing center segregation, was experimentally and theoretically analyzed and following results were obtained.
(1) Continuously cast strand deforms during soft reduction not only in the thickness direction but also in the width and casting directions. The longitudinal elongation and width spreading are proportional to the reduction amount.
(2) Theoretical model to simulate deformation behavior during soft reduction has been developed.
(3) Reduction efficiency defined as the ratio of reduction area for unsolidified region to the total reduction area is expressed as a function of the ratio of unsolidified width to the total strand width and decreases with the decreases in unsolidified width and aspect ratio of the strand.
A test on soft reduction employing conventional one-piece rolls was conducted to analyze the influence of soft reduction and reduction timing on center segregation. As a result, the following findings were obtained. Center segregation was improved when soft reduction was applied only in the final stage of solidification in which the fraction of solid at the slab center is larger than 0.25. When soft reduction was applied employing one-piece rolls over the wide range of solidification stage including the solidification stage with the fraction of solid at the slab center below 0.25, center segregation deteriorated with increasing amount of reduction and the amplitude of variations in center segregation in the casting direction was also increased. It is estimated that the deteriorating tendency of center segregation by soft reduction on the upper stream side is attributable to the new flow of molten steel caused by uneven reduction due to mechanical factors such as roll bending. For the improvement of center segregation, therefore, the optimization of reduction timing is indispensable especially when mechanical factors of uneven reduction are present.
The deformation-induced macrosegregation in continuous casting of steel has been simulated using a finite-volume scheme. For
that purpose, a two-dimensional heat-flow computation was first performed in a Eulerian reference frame attached to the mold,
assuming a unique solidification path, i.e., a unique relationship between temperature and enthalpy. This gave the stationary enthalpy field in the longitudinal section
of the slab. On the other hand, bulging of the slab between two rolls was calculated in the same section, assuming plane-strain
deformation and using the ABAQUS code. The Lagrangian reference frame was attached to the slab, and the rolls were moved at
the surface until a stationary, bulging deformation profile was reached. The bulging of the surface was then used as an input
condition for the calculation of the velocity and pressure fields in the interdendritic liquid. Using a fairly simple hypothesis
for the deformation of the solid skeleton, the mass conservation and Darcy equations were solved in a Eulerian reference frame.
This calculation was performed in an iterative loop, within which the solute conservation equation was also solved. At convergence
and using the enthalpy field, this calculation allowed to obtain the temperature, the volume fraction of solid, and the average
concentration fields, in addition to the fluid velocity and pressure. It is shown that the positive centerline segregation
of carbon in the slab is well reproduced with this model. The effects of shrinkage and soft reduction were also investigated.
Numerical calculations revealing the relationship between the as-cast structure and cooling conditions in near-net-shape casting of steels are presented. The solidification behaviour of steels of different composition was investigated for different process conditions with a one-dimensional heat-flow model. The dependence of the secondary dendrite arm spacing (SDAS) on the distance from the chill surface was determined on the basis of the empirical relationship between local solidification time and SDAS. The numerical results were compared with experimental values of SDAS for a stainless steel, a carbon tool steel and a high-speed steel, resp. Reasonable agreement of model calculations with the experimentally determined SDAS was obtained utilizing time-dependent effective heat-transfer coefficients of the order of 2.5 to 4.5 · 103 W/m2K for typical thin-slab dimensions and 6.0 · 103 W/m2K for thin-strip casting. Es wird über numerische Berechnungen zur Ermittlung des Zusammenhanges zwischen Gußgefüge und Abkühlbedingungen beim endabmessungsnahen Gießen von Stahl berichtet. Das Erstarrungsverhalten von Stählen unterschiedlicher Zusammensetzung wurde mit einem eindimensionalen Wärmeflußmodell für verschiedene Prozeßbedingungen untersucht. Die Abhängigkeit des sekundären Dendritenarmabstandes (SDAS) vom Abstand zur gekühlten Oberfläche wird auf der Basis der empirischen Beziehung zwischen lokaler Erstarrungszeit und SDAS bestimmt. Die numerischen Ergebnisse werden mit experimentellen Werten der SDAS für nichtrostenden Stahl, unlegierten Werkzeugstahl und einen Schnellarbeits-stahl verglichen. Eine gute Übereinstimmung der Modellberechnungen mit den experimentell ermittelten lokalen SDAS wurde unter Benutzung effektiver zeitunabhängiger Wärmeübergangskoeffizienten im Bereich von 2.5 bis 4.5 · 103 W/m2K für typische Abmessungen von Dünnbrammen und 6.0 · 103 W/m2K für das Dünnbandgießen erreicht.
A one-dimensional mathematical model for calculating temperature, strain and segregation distributions has been developed to predict the fluctuated macrosegregation phenomenon in the continuous casting process. The governing differential equations of the mathematical model have been solved simultaneously. Two industrial samples of different carbon-steel alloys under various cooling and casting conditions have been simulated to verify this model quantitatively and qualitatively. A good agreement was obtained between the predicted and measured compositions. The model has demonstrated that this form of segregation is quite sensitive to rapid cooling conditions in the primary stages in continuous casting. A harmonic relationship has been found between the segregation profile and strain behaviour that was mainly obtained within the interdendritic strain region in the mushy zone.
Model for computation of macrosegregation in slabs due to bulging. Assumptions involved. Simplification for the case of no bulging. Introduction of a modified stream function for the mushy zone. Computation of macrosegregation profiles for various conditions. Modell zur Berechnung von Makroseigerungen in Brammensträngen, die durch Ausbauchungen entstehen. Annahmen. Vereinfachungen für den Fall, daß keine Ausbauchungen stattfinden. Einführung einer modifizierten Stromfunktion für die heterogene Schicht. Berechnung der Seigerungsprofile für verschiedene Bedingungen. Modèle pour le calcul de ségrégations majeures en brames dues aux gonflements. Suppositions. Simplification pour le cas qu'il n'y a pas de gonflements. Introduction d'une fonction de courant modifiée pour la zone hétérogène. Calcul des profils de ségrégation pour des conditions différentes.
Hot isostatic pressing (HIP) experiments using the metal analogue materials camphene and succinonitrile are described. Data obtained previously from uniaxial creep experiments are used in densification rate equations for HIP taken from the literature, and the predicted densification behaviour is compared with experimental data. The HIP equations are then modified to include two different representations of the friction stress arising from a dispersed phase of fine, hard particles. In each case the modified theory adequately describes the experimental data.
The effect of a. dispersed phase of small, hard particles on the creep behaviour of two plastic crystals, camphene and succinonitrile, is investigated experimentally. Three models describing the creep deformation of a material containing hard particles are compared to the experimental data. Previous work has considered the particles to result in a constant friction stress which opposes creep deformation. The experimental results for plastic crystals are shown to be equally consistent with a model in which the friction stress is a linear function of the applied stress.
Measurements are reported of the liquid and liquid–solid mixture (mush) densities of succinonitrile–acetone (SCN–ACE) alloys for use in crystal growth and solidification studies. The measured data for the liquid is analyzed and consolidated into a correlation that expresses the liquid density as a function of composition and temperature. This correlation also allows for the calculation of the thermal and solutal coefficients of volume expansion for liquid SCN–ACE alloys. Using the measured results for the liquid–solid mixture densities, the solid densities of SCN–ACE alloys during solidification in a mushy mode are estimated based on either the Lever or Scheil solidification model, and are found to be close to solid densities for pure SCN.
The paper discusses the pros and cons of a process shortening in terms of effectiveness and flexibility. A combined casting/metal-forming process offers great potential for process shortening. This is documented in detail for the case of the double-roller technique of steel strip manufacture. The interlinking of casting and forming provides an integrated analysis of the liquid phase, the solidification process and the directly-linked forming operation which follows solidification. The paper describes various models and their application for the analysis of the process cycle and the resulting properties of the product. Close attention is also given to determining the high temperature yield stress and the heat transmission coefficient for this ultra-high temperature forming process.
The creep of polycrystalline camphene and succinonitrile was studied in uniaxial compression at temperatures of 273 and 293 K. Succinonitrile exhibited classic power-law creep under all conditions with a stress exponent of 5.4 +/- 0.1. Camphene showed power-law creep at higher stresses with an exponent of 4.7 +/- 0.1. However, at lower stresses, camphene exhibited diffusion creep. The minimum applied stress in each material was not sufficiently low to identify a threshold stress for creep. The creep of particle-hardened alloys was modelled using camphene and succinonitrile containing a dispersion of alumina particles of average size 0.4 mum. The volume percentage of alumina was varied from 0 to 6.6% for camphene-alumina and from 0 to 4.8% for succinonitrile-alumina. Creep measurements were made at 273 and 293 K. In all cases, creep was found to obey a power-law. The stress exponent increased by factors of up to 3 for camphene-alumina, and 2 for succinonitrile-alumina. The data could be described with the same stress exponent as that of the unalloyed systems by subtracting a back stress from the applied stress.
Steady-state theories of dendritic solidification are reviewed, and three nonisothermal theories, expressed as simple power laws, are chosen for experimental verification. Specifically, the axial growth rate,V, of a freely growing dendrite can be expressed asV =βGΔθ
n
, wheren andβ are the exponent and prefactor derived from each theory,G is a lumped material parameter, andΔθ is the supercooling. Succinonitrile, a low entropy-of-fusion plastic crystal, was prepared in several states of purity as the test system, and dendritic growth was studied both in the usual manner in long tubes, and in a novel apparatus in which the conditions for “free” dendritic growth were attained. Kinetic measurements show that only when “free” growth conditions obtain are the data reconcilable with current theory in the form discussed above. In particular, we show thatn = 2.6, in agreement with the theories of Nash and Glicksman and that of Trivedi; however, the prefactorsβ of those theories do not agree with the value determined for succinonitrile, which is the only substance for whichG is known accurately. Tip radius measurements, taken over a relatively narrow range of supercooling, when combined with the growth rate data prove that the Peclet number-supercooling relationship derived for each of the three nonisothermal steady-state theoriesall agree with experiment. This curious agreement, along with the inability to “decompose” the Peclet numbers into acceptable velocity-supercooling and tip radius-supercooling relationships is explained on the basis of the limitations imposed by the steady-state assumption itself. Directions for future theoretical and experimental investigation are discussed in the light of the findings presented.
A basic model of the transport phenomena occurring during solidification of multicomponent mixtures is presented. The model
is based on a two-phase approach, in which each phase is treated separately and interactions between the phases are considered
explicitly. The macroscopic transport equations for each phase are derived using the technique of volumetric averaging. The
basic forms of the constitutive relations are developed. These relations link the macroscopic transport phenomena to microscopic
processes such as microstructure development, interfacial stresses, and interfacial heat and mass transfer. Thermodynamic
relations are presented, and it is shown that nonequilibrium effects can be addressed within the framework of the present
model. Various simplifications of the model are examined, and future modeling needs are discussed.
Temperature and time-dependent measurements of the Vickers microhardness of camphene, camphor, succinonitrile and their composites with alumina particles have been made. The materials have previously been shown to be good analogues of metals as regards their creep behaviour. The indentation creep behaviour of these materials at relatively high homologous temperatures provides new information about the indentation creep process, and is found to be consistent with a back/internal stress description of indentation creep.
Alloys generally solidify dendritically, and associated with that is the microsegregation of impurities. Pure metals also solidify in dendritic form as 'thermal' dendrites, which actually segregate the system's enthalpy. In this investigation, small additions of solute to succinonitrile have been studied and dendritic growth observed in a supercooled melt. This free dendritic growth-mode is similar to that experienced by equiaxed dendrites found in alloy castings. Observations of these free dendrites include measurement of velocity and tip radius of the dendrites at different supercoolings and solute concentrations.
- M E Glicksman
- R J Schaefer
- J D Ayers
M.E. Glicksman, R.J. Schaefer, and J.D. Ayers: Metall. Trans. A, 1976,
vol. 7A, pp. 1747-59.
- M A Chopra
- M E Glicksman
- N B Singh
M.A. Chopra, M.E. Glicksman, and N.B. Singh: Metall. Trans. A,
1988, vol. 19A, pp. 3087-96.
349-61.
thicknesses. It is found that the deformation induces not 20
- D L Ceynar
- C Beckermann
- T Fujimura
- K Kushida
- K Sorimach
amount and start time for different initial and final test cell
14. L.K. Chiang: 72nd Steelmaking Conf. Proc., Iron and Steel Society,
Chicago, IL, 1989, pp. 81-89.
thicknesses. It is found that the deformation induces not
20. D.L. Ceynar and C. Beckermann: J. Crystal Growth, 2001, vol. 222,
15. T. Fujimura, K. Kushida, and K. Sorimach: CAMP-ISIJ, 1989, vol. 2
(4), pp. 1166-69.
pp. 380-91.
- S Thiem
- W Loser
S. Thiem and W. Loser: Steel Res., 1992, vol. 63, pp. 291-96.
fixed insulating plate representing the centerline in a slab.
Jonas of the solid growth and deformation behaviors. The experiet al
- E Essadiqi
- L E Collins
- M T Shehata
- L K Chiang
melting point. Its transparency allows for direct observation
3. E. Essadiqi, L.E. Collins, M.T. Shehata, and L.K. Chiang: 2nd Canada-
Japan Symp. Modern Steelmaking and Casting Techniques, J.J. Jonas
of the solid growth and deformation behaviors. The experiet al., eds., TMS-CIM, Toronto, 1994, pp. 251-64.
This alloy not only 1
- Utilizing
- Scn-Ace
utilizing the transparent alloy SCN-ACE. This alloy not only
1. M. Kawaberi, Y. Yamamoto, and K. Asoh: Kawasaki Steel Giho, 1994,
solidifies like many technologically important metal alloys,
vol. 26 (1), pp. 26-32.
Miyahara: els that predict both solid deformation and liquid flow during CAMP-ISIJ
- H Kobayashi
- S Kuriyama
- T Masaoka
- M Suzuki
H. Kobayashi, S. Kuriyama, T. Masaoka, M. Suzuki, and S. Miyahara:
els that predict both solid deformation and liquid flow during
CAMP-ISIJ, 1989, vol. 2 (4), pp. 1158-61.
Deformation is induced by the movement 5 Iron Steel of a cooled side wall (i.e., the heat exchanger) toward a Inst
- S Ogibayashi
- M Kobayshi
- M Yamada
- T Mukai
tion of steel slabs. Deformation is induced by the movement
5. S. Ogibayashi, M. Kobayshi, M. Yamada, and T. Mukai: Iron Steel
of a cooled side wall (i.e., the heat exchanger) toward a
Inst. Jpn. Int. 1991, vol. 31, pp. 1400-07.
- G C Davies
- D R H Jones
G.C. Davies and D.R.H. Jones: Acta Mater., 1997, vol. 45, pp. 775-89.
25. J. Ni and C. Beckermann: Metall. Trans. B, 1991, vol. 22B, pp.
solidification behavior and deformation-induced transport 10. M. El-Bealy and H. Fredriksson: Scand The relatively simple experimental setup
solidification behavior and deformation-induced transport
10. M. El-Bealy and H. Fredriksson: Scand. J. Metall., 1994, vol. 23, pp.
phenomena. The relatively simple experimental setup,
140-50.
Modern Steelmaking and Casting Techniques
- E Essadiqi
- L E Collins
- M T Shehata
- L K Chiang
- E. Essadiqi
Solid State Phenomena
- G Lesoult
- S Sella
- G. Lesoult