Showing papers on "Directional solidification published in 2013"
TL;DR: In this paper, the authors investigated the impact of the morphological and crystallographic texture on the competitive growth of selective laser melting (SLM) of a metal powder with a preferential crystal orientation along the building direction.
467 citations
TL;DR: The results show that both structure and mechanical properties of the freeze-cast composites can be custom-designed and that they are thus ideally suited for a large variety of applications that require high porosity at low or medium load-bearing capacity.
103 citations
TL;DR: In this paper, the survival of unfavorably oriented dendrites and highly complicated dendrite-dendrite interactions in three-dimensional space during the directional solidification of a binary alloy were observed for the first time through very large-scale phase-field computations performed by a graphics processing unit (GPU) supercomputer and a high-performance algorithm developed for parallel computing.
102 citations
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06 Aug 2013TL;DR: In this paper, the authors report the results of experiments aimed at identifying the sources of high temperature creep resistance and high levels of strength in a two phase Al2O3/ZrO2(Y 2O3) system.
Abstract: The eutectic architecture of a continuous reinforcing phase within a higher volume fraction phase or matrix, can be described as a naturally occurring in-situ composite. Here we report the results of experiments aimed at identifying the sources of high temperature creep resistance and high levels of strength in a two phase Al2O3/ZrO2(Y2O3) system. The mechanical properties of two phase Al2O3/ZrO2(Y2O3) eutectic are superior to that of either constituent alone due to strong constraining effects provided by the coherent interfaces and micrsostructure. The Al2O3/ZrO2(Y2O3) eutectic maintains a low energy interface resulting from directional solidification and can produce strong and stable reinforcing phase/matrix bonding. The phases comprising a eutectic are thermodynamically compatible at higher homologous temperatures than man-made composites and as such offer the potential for superior high temperature properties.
97 citations
TL;DR: In this paper, the development of the chimney and the probability of their surviving depend sensitively on the spatial and temporal properties of the flow field, and variations of the vertical temperature gradient along the solidification cell lead to the observation of different mechanisms for chimney formation.
Abstract: The directional solidification of Ga-25wt pct In alloys within a Hele-Shaw cell under the influence of thermosolutal convection was observed by means of X-ray radioscopy. The unstable density stratification at the solidification front causes the formation of rising plumes containing solute-rich liquids. The development of the chimneys and the probability of their surviving depend sensitively on the spatial and temporal properties of the flow field. Variations of the vertical temperature gradient along the solidification cell lead to the observation of different mechanisms for chimney formation. Perturbations of the dendritic structure are the origin of development of segregation freckles in case of low temperature gradients. The long-term stabilities of these segregation channels are strongly influenced by the transient nature of the melt convection. The situation at higher temperature gradients is characterized by two dominating convection rolls in the liquid phase which are driven by a lateral temperature gradient and the convex shape of the solidification front. The penetration of this flow pattern into the mushy zone results in continuous accumulation of solute in the central part of the mushy zone followed by a remelting of the solid fraction and the occurrence of a stable chimney.
81 citations
TL;DR: Results of directional solidification experiments conducted on board the International Space Station and quantitative phase-field modeling of those experiments reveal the existence of oscillatory breathing modes with time periods of several 10's of minutes.
Abstract: We report results of directional solidification experiments conducted on board the International Space Station and quantitative phase-field modeling of those experiments. The experiments image for the first time in situ the spatially extended dynamics of three-dimensional cellular array patterns formed under microgravity conditions where fluid flow is suppressed. Experiments and phase-field simulations reveal the existence of oscillatory breathing modes with time periods of several 10's of minutes. Oscillating cells are usually noncoherent due to array disorder, with the exception of small areas where the array structure is regular and stable.
73 citations
TL;DR: In this paper, the microstructural evolution of Mg-3, 6 and 9-wt. alloys with respect to the solidification parameters such as thermal gradient (G), solidification velocity (V), cooling rate (G·V) and solute (Al) content were investigated.
65 citations
TL;DR: In this paper, a dendritic needle network (DNN) model is proposed for simulating quantitatively the solidification of Dendritic alloys, which is intended to reliably bridge the gap between phase-field simulations on the scale of dendrite tip radius ρ and cellular-automaton simulations on a several orders of magnitude larger scale of an entire dendrick grain.
65 citations
TL;DR: In this paper, the effects of terbium additives on the microstructure and magnetic properties of Fe83Ga17Tbx alloys (x = 0, 0.2, 0., 0.4, 0, 6, and 0.8) were investigated.
Abstract: We present the effects of terbium additives upon the microstructure and magnetic properties of Fe83Ga17Tbx alloys (x = 0, 0.2, 0.4, 0.6, and 0.8), prepared by vacuum electric arc-melting and directional solidification techniques. Experiments indicate that small amounts of terbium more than double the saturation magnetostriction of a [110] textured Fe83Ga17 alloy with λ = 72 × 10−6 and lower the magnetostriction saturation field. The pronounced increase in magnetostriction stems from the appearance of [100] texture in polycrystalline alloys. It is verified that [110] and [100] textures are enhanced by the introduction of terbium atoms preferentially residing in a Tb-rich intergranular phase.
62 citations
TL;DR: In this article, the authors summarize experimental and numerical studies particularly concerned with applications of rotating magnetic fields (RMF) or travelling magnetic field (TMF) to directional solidification of metal alloys.
Abstract: In this minireview, we summarize experimental and numerical studies particularly concerned with applications of rotating magnetic fields (RMF) or travelling magnetic fields (TMF) to directional solidification of metal alloys. After introducing some fundamentals of electromagnetic stirring, we review the insights gained into flow-induced modifications of microstructure and the formation of freckles and macrosegregations. We further discuss recent strategies, using time-modulated RMF and TMF, which aim to overcome the deficiencies of conventional stirring, in particular flow-induced macrosegregation, by effectively controlling the flow field. On the microscale, we show that time-varying flows are able to alter the sidebranch characteristics vital to the potential of fragmentation.
60 citations
TL;DR: In this paper, the conditions to grow bulk Si crystals from Si-Sn melts were consistent with the constitutional supercooling criterion, and the growth process was confirmed to be controlled by the diffusion of Si for the present growth conditions.
TL;DR: In this article, the microstructure parameters were expressed as functions of solidification parameters by using a linear regression analysis, and the dependency of HV, σ on the cooling rate, microstructures and composition were determined.
Abstract: Al(100−x)-Cux alloys (x=3 wt%, 6 wt%, 15 wt%, 24 wt% and 33 wt%) were prepared using metals of 99.99% high purity in vacuum atmosphere. These alloys were directionally solidified under steady-state conditions by using a Bridgman-type directional solidification furnace. Solidification parameters (G, V and ), microstructure parameters (λ1, λ2 and λE) and mechanical properties (HV, σ) of the Al-Cu alloys were measured. Microstructure parameters were expressed as functions of solidification parameters by using a linear regression analysis. The dependency of HV, σ on the cooling rate, microstructure parameters and composition were determined. According to experimental results, the microhardness and ultimate tensile strength of the solidified samples was increased by increasing the cooling rate and Cu content, but decreased with increasing microstructure parameters. The microscopic fracture surfaces of the different samples were observed using scanning electron microscopy. Fractographic analysis of the tensile fracture surfaces showed that the type of fracture significantly changed from ductile to brittle depending on the composition.
TL;DR: In this paper, non-basal slip systems in the Mg12ZnY long-period stacking ordered (LPSO) phase, the operational frequency of which is increased at high-temperatures and affects the mechanical properties, were clarified.
Abstract: Non-basal slip systems in the Mg12ZnY long-period stacking ordered (LPSO) phase, the operational frequency of which is increased at high-temperatures and affects the mechanical properties, were clarified. The f1 100gh11 20i prism slip was identified in both 18R and 14H LPSO phases, even though they have the different lattice systems. This behavior is different from that observed in a Ni-based LPSO phase. The peculiar chemical modulation in the Mg12ZnY LPSO phase may affect the selection of operative slip systems. [doi:10.2320/matertrans.MI201208]
TL;DR: In this article, a comparison between the in situ and real-time observation of a directional solidification experiment carried out at the European Synchrotron Radiation Facility and a direct simulation of grain structure formation in the sample using a two-dimensional cellular automaton-finite element (CA-FE) model is presented.
TL;DR: In this article, the microstructural characterisation, mechanical testing and fractography investigation were performed on twinning induced plasticity (TWIP) steels, fabricated with resistance spot welding, and failure mode during the cross-tensile test was found to follow the sequences of strain localisation of both sheets, crack initiation at notch tip, crack following along the fusion boundary and finally, ductile shear fracture along the sheet thickness direction.
Abstract: In this study, the microstructural characterisation, mechanical testing and fractography investigation were performed on twinning induced plasticity (TWIP) steels, fabricated with resistance spot welding. Failure mode during the cross-tensile test was found to follow the sequences of strain localisation of both sheets, crack initiation at notch tip, crack following along the fusion boundary and, finally, ductile shear fracture along the sheet thickness direction. On the other hand, failure in the tensile shear test was always directed along the sheet/sheet (s/s) interface; the interfacial failure and shear deformation were observed at the weld centreline. Solidification occurred as a primary austenitic solidification mode, and no martensitic transformations were detected through electron backscatter diffraction analysis. The fusion zone was mainly composed of austenite with directional solidification towards the centreline; the columnar dendritic and equiaxed structures were identified. Interdendr...
TL;DR: In this article, a facility was designed and developed to investigate directional solidification on metallic alloys in microgravity conditions with in situ X-ray radiography observation, which was used to validate the experimental results.
TL;DR: This article used the laser floating zone method to texture Bi2Ba2Co2Ox thermoelectric ceramics at a growth rate of 5mm/h−1.
TL;DR: In this paper, directional solidification experiments were carried out with Sn-0.7.wt.%Ni alloys and interrelations of solidification thermal parameters, microstructure, and tensile properties have been established.
Abstract: Environmental concerns over the toxicity of Pb are resulting in the progressive ban of Pb-based solders as part of electrical and electronic devices. Sn-Cu alloys are becoming interesting Pb-free solder alternatives. In the case of hypoeutectic Sn-Cu alloys (<0.7 wt.% Cu), small alloying additions of Ni can prevent the growth of coarse and deleterious Cu6Sn5 particles. Solidification thermal parameters such as the growth rate, cooling rate, and interfacial heat transfer coefficient (h
i) determine the morphology and scale of the phases forming the resulting microstructure. In the present study, directional solidification experiments were carried out with Sn-0.7 wt.%Cu, Sn-0.7 wt.% Cu-0.05 wt.%Ni, and Sn-0.7 wt.%Cu-0.1 wt.%Ni alloys and interrelations of solidification thermal parameters, microstructure, and tensile properties have been established. The highest time-dependent h
i profile was found for the Sn-0.7 wt.%Cu-0.1 wt.%Ni alloy, which is an indication that this alloy has the highest fluidity. Constrained dendritic arrangements were observed for all alloys experimentally examined. This morphology has been associated with high cooling rates and growth rates. Cellular regions, characterized by aligned eutectic colonies, were also observed to occur for cooling rates lower than 0.9 K/s and 6.0 K/s for the unmodified Sn-0.7 wt.%Cu alloy and for both Ni-modified Sn-Cu alloys, respectively. Experimental Hall–Petch-type equations correlating the ultimate tensile strength and elongation with cell/dendritic spacings are proposed.
TL;DR: In this paper, it was shown that the ice crystal growth in food and biomaterials is a function of the freezing rate, and that the food freezing process is reasonably comparable to the solidification process in alloys, as is apparent in the comparable exponent in the fitted scaling rule with the one commonly used in alloy solidification.
TL;DR: In this paper, the grain boundary groove evolution mechanisms during solidification have been studied and the shape and evolution revealed grain competition phenomena and were drastically modified by the occurrence of new grains or twins.
TL;DR: In this paper, the authors have revealed the solidification path of 18-8 austenitic stainless steel using directional solidification and liquid quenching, and confirmed that austenite is formed through peritectic transformation rather than eutectic reaction.
TL;DR: In this paper, heat transfer characteristics were investigated at different stages in cold crucible directional solidification (CCDS) and a dimensionless parameter K (axial-to-radial heat flux density ratio) was defined and used to characterize the direction of heat flux, the effects of the temperature gradient (G L ), the current frequency ( f ), and the pulling rate ( u ) were evaluated.
TL;DR: In this paper, a dual-phase (β-Ni518Mn314In168 and γ-Ni624Mn325In51) Ni52Mn32In16 alloy prepared by the zone melting liquid metal cooling directional solidification method was presented.
TL;DR: In this paper, the twinning phenomenon has been identified and observed in situ and in real time during the solidification using X-ray synchrotron imaging techniques: radiography and topography.
15 Apr 2013-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a transient directional solidification system was used, which permitted the assessment of microstructures along castings lengths of hypereutectic Sn-2.0 and 2.8% Cu alloys, for a wide spectrum of experimental tip growth rates (V L ) and tip cooling rates (T • ).
Abstract: In this study a transient directional solidification system was used, which permitted the assessment of microstructures along castings lengths of hypereutectic Sn–2.0 wt% and 2.8 wt% Cu alloys, for a wide spectrum of experimental tip growth rates ( V L ) and tip cooling rates ( T • ). The primary Cu 6 Sn 5 IMC developed typical M-shaped or H-shaped morphologies. However, rod-like particles prevailed along the Sn-rich β matrix of both alloys evaluated. Smaller inter-branch spacings ( λ ) are shown to be associated with the alloy having higher Cu content, and the presence of Cu 3 Sn (e) intermetallic compound (IMC) was detected by X-ray diffraction (XRD). Such IMC developed probably due to the combination of high cooling rates during solidification and incomplete peritectic reaction along the Cu-enriched regions of the casting, which provided less η than predicted under equilibrium conditions. Hall–Petch type relationships are proposed interrelating Vickers hardness (HV), ultimate tensile strength ( σ u ) and elongation to fracture against λ . The two alloys examined showed roughly similar trends considering HV and σ u , despite having a very different ductility behavior. However, the mechanical strength of each alloy is shown to be controlled by different microstructure features. The higher fraction of eutectic rod-like Cu 6 Sn 5 intermetallics observed for the Sn–2.0 wt% Cu alloy was shown to be associated with the corresponding higher experimental mechanical strength.
TL;DR: In this article, the columnar to equiaxed transition and primary dendritic arm spacings of Al-3wt.%Si alloy were investigated during horizontal directional solidification.
Abstract: The main purpose of this paper is to investigate both the columnar to equiaxed transition and primary dendritic arm spacings of Al-3wt.%Si alloy during the horizontal directional solidification. The transient heat transfer coefficient at the metal-mold interface is calculated based on comparisons between the experimental thermal profiles in castings and the simulations provided by a finite difference heat flow program. Simulated curve of the interfacial heat transfer coefficient was used in another numerical solidification model to determine theoretical values of tip growth rates, cooling rates and thermal gradients that are associated with both columnar to equiaxed transition and primary dendritic arm spacings. A good agreement was observed between the experimental values of these thermal variables and those numerically simulated for the alloy examined. A comparative analysis is carried out between the experimental data of this work and theoretical models from the literature that have been proposed to predict the primary dendritic spacings. In this context, this study may contribute to the understanding of how to manage solidification operational parameters aiming at designing the microstructure of Al-Si alloys.
TL;DR: In this article, the influence of casting and baffle geometry, mold thickness as well as withdrawal speed on solidification conditions and resulting microstructure was examined for the case of simple cylindrical castings and found that the nature of the baffle has a stronger effect than the different mechanism of heat dissipation.
TL;DR: In this article, the authors investigated the mechanism of competitive growth during the directional solidification with bi-crystal superalloy AM3 and proposed that the factor contributing to the competitive growth was the rotation angle of the unfavorably oriented grain.
TL;DR: In this article, several three-dimensional coupled unsteady calculations are carried out for a 22×22×11 cm3 silicon melt directionally solidified in a traveling magnetic field.
TL;DR: In this article, the authors investigated the relationship between the scale of the minority phase of the monotectic microstructure and the corresponding wear behavior in Al-5.5 Wt% In Alloy.