Showing papers on "Directional solidification published in 2014"
TL;DR: In this article, the competitive growth of dendrites at the converging grain boundaries (GBs) of bicrystals during the directional solidification of an Al-Cu alloy was investigated by means of two-dimensional phase-field simulations.
116 citations
TL;DR: In this paper, the authors considered the directional solidification of Al-7 ¼ ¼ Si alloys under the influence of strong electric currents for the configuration of two parallel electrodes immersed from the free surface into the solidifying alloy, and demonstrated that the grain refining effect observed in these experiments can be attributed solely to the forced melt flow driven by the Lorentz force.
108 citations
TL;DR: In this article, an approach to grain control using seed-assisted growth in directional solidification (DS) is reported, where proper multi-crystalline silicon seeds at the bottom of the crucible provided numerous fine nucleation points for the controlled grain growth in an optimized hot-zone.
88 citations
TL;DR: In this paper, a coupling of the Kampmann-Wagner numerical (KWN) model to CALPHAD was carried out to predict the as-cast grain size of inoculated multicomponent aluminum alloys.
86 citations
TL;DR: In this paper, the microstructure evolution and mechanical properties of the samples were investigated as a function of withdrawal rate, which could be characterized by the decreased mean diameter of cellular eutectic, mean diameter and mean interphase spacing.
67 citations
TL;DR: Based on the concentration distributions of aluminum and calcium along the growth direction, the removal mechanism of such impurities with both high saturated vapor pressures and low segregation coefficients is investigated in this paper, where the results show that the removal of this type of impurities only depends on evaporation during vacuum induction melting process, thus their contents decrease significantly due to the strongly eva-oration under the high temperature and high vacuum conditions.
63 citations
TL;DR: In this article, a Co1.5 high-entropy alloy has been investigated for its high-temperature microstructural stability, which is shown to possess mainly a face-centered cubic (FCC) structure.
Abstract: In the present study, a Co1.5CrFeNi1.5Ti0.5 high-entropy alloy has been investigated for its high-temperature microstructural stability. This material is shown to possess mainly a face-centered cubic (FCC) structure; the η phase is present at the interdendritic region in the as-cast condition, and it is stable between 1073 K and 1273 K (800 °C and 1000 °C); γ′ particles are found throughout the microstructures below 1073 K (800 °C). Segregation analysis has been conducted on a single crystal sample fabricated by a directional solidification process with a single crystal seed. Results show that Co, Cr, and Fe partition toward the dendritic region, while Ni and Ti partition toward the interdendritic areas. Scheil analysis indicates that the solid–liquid partitioning ratio of each element is very similar to those in typical single crystal superalloys.
63 citations
TL;DR: In this paper, six alloys were directionally solidified at low growth speeds (1-5μm−s −1 ) under a weak transverse magnetic field (⩽0.5 T ) by means of synchrotron X-ray radiography and it was observed that dendrite fragments and equiaxed grains were moved approximately along the direction perpendicular to the magnetic field.
61 citations
TL;DR: In this paper, the growth behavior inside and above seed gaps during directional solidification of monocrystalline lab-scale silicon ingots was investigated, and it was shown that the silicon melt filled the gaps rapidly and monocrystaline growth started in most cases at the seed side walls toward the gap center.
61 citations
TL;DR: In this paper, a modified vacuum directional solidification system for producing multicrystalline silicon (mc-Si) was proposed, where the temperature distribution, melt convection, melt-crystal interface and thermal stress were simulated.
54 citations
TL;DR: In this paper, the evolution of the solid-liquid interface morphology during the initial transient of directional solidification is investigated by quantitative phase-field numerical simulation during cooling down of an Al-4.wt.% Cu alloy growing in the preferred 〈1.0 ͡ 0͡ ǫ-direction.
TL;DR: In this paper, cracks are mostly initiated by the fragmentation or cleavage of perforated β-phase platelets, in addition to that of coarse Si particles and undissolved Cu-intermetallics.
TL;DR: In this article, the electron backscattered diffraction (EBSD) analyses of the grains at different pulling rates, i.e., 1, 5, and 20 cm/h, were carried out.
TL;DR: In this article, a mold geometry was designed to evaluate a range of thermal conditions during solidification and assess the tendency for lateral growth in liquid metal-cooling (LMC) directional solidification process.
TL;DR: In this article, a 3D phase-field numerical model is used to analyze the growth direction and stability of a monocrystal growing in a thin sample by a single layer of homogeneously spaced microstructures.
TL;DR: In this article, the thermal gradient (GL), structural refinement, micro-segregation and porosity distribution of the Bridgman process was assessed in terms of the structural refinement of the process.
TL;DR: The columnar-to-equiaxed transition (CET) observed in the dendritic grain structure of the refined alloys, sharp or progressive, is defined and characterized based on the profile of the averaged elongation factor as mentioned in this paper.
22 Sep 2014-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the authors show that the interlamellar space of the directionally solidified samples decreases from the average 1650nm of as-cast to less than 565nm and is more homogeneous.
Abstract: The as-cast Ti44Al6Nb1.0Cr2.0V alloy master ingot was prepared by vacuum consumable melting technology. Some bars were cut from this ingot and they were directionally solidified by cold crucible under different pulling velocities. The samples could be well directionally solidified when the power (P) was 45 kW and the pulling velocity (V) was 8.33 μm/s or 11.67 μm/s. The results show that the interlamellar space of the directionally solidified samples decreases from the average 1650 nm of as-cast to less than 565 nm and is more homogeneous. The microcrack in the master ingot can be eliminated completely and the room temperature (RT) tensile property is also improved after cold crucible directional solidification (CCDS). The ultimate tensile strength (UTS) is 602.5 MPa and the elongation is 1.20% as P=45 kW and V=11.67 μm/s, compared with as-cast 499 MPa of UTS and 0.53% of elongation. Trans-granular and trans-lamella fractures are predominant modes. The relationship between CCDS interlamellar space (d) and the pulling velocity can be described as d = 1783.2 V − 0.554 and r 1 2 = 0.972 , where r 1 2 is the corresponding regression coefficient. The CCDS interlamellar space and nanoindentation hardness (HN) in the lamella region can be described as H N = 17.95 d − 0.145 and r 2 2 = 0.986 , and they are changed as H N ′ = 14.03 d ′ − 0.104 and r 3 2 = 0.975 when the cast condition is considered. The nanoindentation hardness of the B2 phase and the block γ phase are about 8.89 GPa and 8.15 GPa, respectively; both of them keep almost the same in different conditions.
TL;DR: In this paper, the grain selection process during single crystal casting of a Ni-base superalloy DD403 in spiral grain selector is simulated by a macro-scale ProCAST coupled a meso-scale Cellular Automaton Finite Element (CAFE) model.
TL;DR: In this article, a combination of synchrotron x-ray radiography and white-beam xray topography was used to reveal the deformations that dendritic microstructures undergo during the upward directional solidification of Al-7wt.%Si alloys.
Abstract: The in situ investigation of dendrite deformation during solidification processing is an ongoing challenge because of the technical difficulties in carrying out experimental observations and direct measurements in metallic systems that are opaque to visible light and have a high melting temperature. Over the last 20 years, x-ray imaging has been established as a method of choice to overcome this experimental barrier by taking advantage of the increased capabilities of third-generation synchrotron x-ray sources, providing information on growth process and semisolid deformation that is not available otherwise. In this article, we present results showing that the unique combination of synchrotron x-ray radiography and synchrotron white beam x-ray topography can help to reveal the deformations that dendritic microstructures undergo during the upward directional solidification of Al-7wt.%Si alloys. Particular focus will be placed on the bending phenomena of dendrites because of gravity, which may precede fragmentation in the case of well-developed secondary arms.
TL;DR: An analytical solution of the heat conduction equation was used as a novel approach to control the solidification velocity during the process and the relationships between processing conditions and resulting structure as well as between structure and mechanical properties were elucidated and discussed.
TL;DR: In this article, three experimental techniques, namely, mushy zone quenching (MZQ), planar directional solidification followed by quenched (PDSQ), and random sampling (RS), were implemented for the analysis of microsegregation tendency and the magnitude of solute elements by electron probe microanalysis.
TL;DR: In this paper, the evolution of the morphology of MC carbides with the change of cooling rate and carbon content in two kinds of nickel-base superalloys, K417G and DD33, has been investigated.
TL;DR: In this article, a directional solidification experiment was carried out with the Bi-2.5-wt%Ag eutectic so that a large range of cooling rates (T ) could be obtained under unsteady state conditions.
TL;DR: In this paper, it was shown that the quantity of hardening (fracture toughness) is proportional to the content of the transformable t phase, and that increasing the stabilizing impurity concentration leads to an increase in the volume fraction of the “untransformable” phase.
TL;DR: In this paper, a two-dimensional cellular automaton model with decentered square algorithm is developed for quantitatively predicting the dendritic growth during solidification process, where the growth kinetics of solid/liquid interface are determined by the local equilibrium composition and local actual liquid composition, and the calculation of the solid fraction increment is based on these two compositions to avoid the solution of growth velocity.
TL;DR: In this paper, the analysis of numerical simulation of the Bridgman directional solidification process performed on CMSX-4 rods was studied applying the ProCAST software and the coefficients of the equation were determined and used to calculate the growth rate of dendrite tip.
Abstract: The paper presents the analysis of numerical simulation of the Bridgman directional solidification process performed on CMSX-4 rods. The numerical simulation was studied applying the ProCAST software. The constitutive law parameters of the normal Gaussian distribution were used to describe the nucleation process. The coefficients of the equation were determined and used to calculate the growth rate of dendrite tip. The analysis of the as-cast microstructure was carried out with the use of Aphelion software in order to determine the average area of grains and their quantity. The experimental verification of both nucleation and grain growth coefficients used for the simulation of the directional solidification process confirmed that the model was correct and described well the investigated process of directional solidification using the Bridgman method.
TL;DR: In this article, the authors present the limitation of the cast technique for silicon growth and the obstacle to reduce the dislocation density below 10 3 ǫ cm −2, independent of other dislocation sources.
TL;DR: In this article, a single crystal Ni-base superalloy CMSX-6 was cast by using the downward directional solidification process (DWDS) using withdrawal rates of between 0.0013 and 0.0217 cm/s.
TL;DR: In this paper, the authors aimed at the refinement of primary microstructure appearing in the refractory lightweight structural TiAl-based intermetallics during their solidification from the melt.