Showing papers on "Directional solidification published in 2017"
TL;DR: In this paper, the effects of process parameters including laser power, scan velocity, hatch distance, and scan strategy that produce various solidification cooling rates and thermal gradients during the process, which also contribute to the resultant microstructure, have been analyzed.
Abstract: Laser powder bed fusion (L-PBF) as an additive manufacturing process produces nearly fully dense nickel alloy 625 (IN625) parts with complex features. L-PBF generates surfaces and microstructure through directional solidification that can be controlled by scan strategies and selection of process parameters. This study provides experimental investigations on microstructure formation including sizes of cellular grains and growth directions of columnar grains on the nickel alloy 625 test coupons. The effects of process parameters including laser power, scan velocity, hatch distance, and scan strategy that produce various solidification cooling rates and thermal gradients during the process, which also contribute to resultant microstructure, have been analyzed. Optimization studies are conducted on several objectives to improve the productivity while controlling the process effects on the resultant microstructure using response surface regression, desirability functions, and multi-objective genetic algorithm optimization.
123 citations
TL;DR: In this paper, the authors combine in situ X-ray radiography of a dilute Al-Cu alloy solidification experiments with three-dimensional phase-field simulations to build a microstructure selection map for this alloy.
120 citations
08 Feb 2017-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the eutectic growth of 15 and 18-wt% Si alloys was investigated under transient heat flow conditions and further characterization of the related microstructures.
Abstract: The present investigation deals with directional solidification (DS) of Al-15 wt% and 18 wt% Si alloys under transient heat flow conditions and further characterization of the related microstructures. Emphasis is given on the eutectic growth being affected not only by solidification kinetics but also by melt superheat, which is varied in two degrees for each alloy, i.e., 6% and 23% above the liquidus temperature. The dependences of interphase spacing (λ) on both solidification kinetics (fast, intermediate and slow cooling conditions) and on melt superheat during solidification of hypereutectic alloys are reported for the first time. Furthermore, functional experimental interrelations of tensile mechanical properties and interphase spacing between eutectic Si particles of both alloys evaluated are proposed. It is shown by these correlations that the tensile properties increase with the decrease in these spacings. More significant variations in properties are associated with a certain range of spacings (1.0 µm −1/2 ) has been verified for the present tested alloys and experimental conditions.
54 citations
TL;DR: In this article, the authors investigated the elastocaloric reversibility in Ni-Mn-In-Co meta-magnetic shape memory alloys and found that the asymmetry of the maximum ΔT between loading and unloading strongly depends on the magnitude of superelastic strain.
Abstract: In this letter, we investigate the elastocaloric reversibility in Ni-Mn-In-Co meta-magnetic shape memory alloys. A highly [001] textured Ni45Mn36.5In13.5Co5 polycrystalline alloy was grown by using the liquid-metal-cooling directional solidification technique. We have observed a giant adiabatic temperature change (ΔT) of +8.6 K caused by the stress-driven complete martensitic transformation. The asymmetry of the maximum ΔT between loading and unloading strongly depends on the magnitude of superelastic strain. Such an irreversible behavior is ascribed to the friction energy dissipation as well as the variation of the elastocaloric entropy change by shifting initial temperatures.
53 citations
TL;DR: In this article, the phase-field simulation of a nickel-based superalloy during solidification in three dimensions was investigated using the phasefield method, and the performance of the GPU-based parallel computing method was tested and the results demonstrate that a maximum performance of 774.292 GFLOPS (giga floating-point operations per second) can be obtained using a single NVIDIA GTX1080 GPU.
49 citations
TL;DR: In this paper, high-resolution X-ray radiography and tomography was used to investigate the behavior of colloidal suspensions of alumina particles during directional solidification by freezing, which provided both qualitative and quantitative information about the propagation kinetic of the solid/liquid interface, the particles redistribution between the crystals and a particle enriched phase and the 3D organization of the ice crystals.
Abstract: This paper investigates by in situ high-resolution X-ray radiography and tomography the behaviour of colloidal suspensions of alumina particles 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 particles redistribution between the crystals and a particle enriched phase and the 3D organisation of the ice crystals. In this first part of two companion papers, the precursor phenomena leading to directional crystallisation during the first instants of solidification is 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.
47 citations
TL;DR: In this article, the formation of the grain structure in Al-10-wt%Cu alloy during directional solidification was investigated experimentally and it was demonstrated that fragments detach from the dendrite tip region and move slightly ahead of the solid liquid interface as they grow.
43 citations
TL;DR: In this paper, the mesoscopic envelope model of columnar dendritic growth is compared to phase field simulations in two dimensions, where the phase field model resolves the detailed growth morphology at the microscale, while the mesoscale envelope model describes a dendrite grain by its envelope.
42 citations
TL;DR: High-operating-temperature direct ink writing (HOT-DIW) of mesoscale architectures that are composed of eutectic silver chloride-potassium chloride undergoes directional solidification upon printing on a cold substrate, enabling the manipulation of light in the visible and infrared range.
Abstract: High-operating-temperature direct ink writing (HOT-DIW) of mesoscale architectures that are composed of eutectic silver chloride-potassium chloride. The molten ink undergoes directional solidification upon printing on a cold substrate. The lamellar spacing of the printed features can be varied between approximately 100 nm and 2 µm, enabling the manipulation of light in the visible and infrared range.
41 citations
TL;DR: In this article, the solidification path of single-crystal nickel-base superalloys containing minor carbon was investigated under various laser rapid directional solidification (LRDS) conditions.
40 citations
29 Sep 2017-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effects of minor additions of Ag and Cu on a Sn-34-wt%Bi solder alloys produced by directional solidification were examined and the evolution of tensile strength and ductility as a function of λ 2 was examined.
Abstract: Over the past few years Sn-based solders containing third and fourth elements have become of great interest to try and improve the consistency of solders during application. In most reported cases this involved the addition of either Ni in Sn-Cu or Ag in Sn-Bi solder alloys. Still there is a lack of research showing how the combination of third element additions and varying cooling rates affect the mechanical properties of Sn-Bi-X solder alloys. As such the present investigation examines the effects of minor additions of Ag and Cu on a Sn-34 wt%Bi solder alloys produced by directional solidification. Directional solidification was used as the transient regime attained during directional solidification in a water-cooled mold may allow for similar cooling rates to those found in industrial reflow soldering operations. Microstructural analysis on the Sn-Bi-X alloys was conducted using eutectic spacing (λ E ), Bi precipitates spacing (λ p ) and the secondary dendritic spacing (λ 2 ) measurements. These measurements represented the complex eutectic growth, the solid-state precipitation of Bi within the β-Sn phase and the length-scale of the Sn-rich dendritic array respectively. In conjunction with these measurements the evolution of tensile strength and ductility as a function of λ 2 was examined. Considering the Sn-34 wt%Bi, Sn-34 wt%Bi-0.1 wt%Cu, Sn-34 wt%Bi-0.7 wt%Cu and Sn-33 wt%Bi-2 wt%Ag alloys, it was found that the modified alloys containing 0.7 wt%Cu and 2.0 wt%Ag showed lower tensile properties and lower ductility. In contrast, the addition of 0.1 wt%Cu increased the ductility for λ 2
TL;DR: In this paper, the microstructural patterns formed during liquid to solid phase transformations control the properties of a wide range of materials, including Ni, Fe, and Co alloys, are captured in 4D (3D plus time) using a methodology which exploits three separate advances: a bespoke high temperature environment cell; the development of high X-ray contrast alloys; and a novel environmental encapsulation system.
TL;DR: In this article, a method to determine material parameters by comparing the evolution of experimentally determined 3D microstructures to simulated 3D nano-structures is proposed. But this method is not applicable to other experiments, such as the one in this paper, in which the structure is compared to that measured experimentally at a later time.
TL;DR: In this paper, the mechanism of macrosegregation and modification to dendrite size and spacing from a transverse magnetic field has been modelled through direct numerical simulation and the primary driver for this mechanism was identified as a strong Lorentz force formed in the interdendritic region.
TL;DR: In this article, particle-shaped Tb-rich precipitates are formed and dispersively distributed in the matrix along the (sub-) grain boundaries; preferred 〈100〉 orientation is achieved in the alloys by appropriate directional solidification process, which makes contribution to improve the magnetostriction.
TL;DR: In this article, a combined experimental and simulation approach is taken to investigate the response of a three-phase eutectic system to changes in solidification velocity using Al-Ag-Cu as a model system, large scale three-dimensional phase-field simulations are compared to directionally solidified samples containing both, velocity increases and decreases.
TL;DR: In this article, the effect of static magnetic field on longitudinal macro segregation of primary silicon phase has been investigated in directionally solidified hypereutectic Al-Si alloy.
TL;DR: 2D CFD modeling was used to generate data for the design and training of artificial neural networks and for Gaussian process modeling to assess the complex nonlinear dependences among the parameters and to optimize them for the interface flattening.
TL;DR: In this article, the microstructure evolution and room temperature fracture toughness of as-cast and directionally solidified NiAl-Cr(Fe) alloy were investigated using OM, SEM, EDS, DSC and three-point bending tests.
TL;DR: In this paper, the microstructure of as-cast ingot and three-dimensional microstructures of carbides were analyzed by optical microscope and scanning electron microscope using X-ray diffraction.
TL;DR: In this article, the effect of silicon content on the microstructure (lamellar and flake), mechanical (microhardness, ultimate tensile strength) and electrical resistivity properties of Al-26Cu-Fe-Si quaternary alloys has been investigated.
TL;DR: In this article, a phase-field model based on the Grand potential approach is applied to simulate the eutectic reaction during directional solidification (DS), and two-and three-dimensional simulations of the DS process for three different growth velocities are performed.
TL;DR: In this article, a detailed analysis of the grain structures in the multi-crystalline silicon sheets grown by directional solidification was performed and the free energy change (per unit length) when one or two facets anchor to the groove tri-junction and the critical undercooling for twinning was derived and compared with experiments.
TL;DR: In this article, the effect of interfacial anisotropy on the growth direction selection during directional solidification of alloys by using the thin-interface phase-field model was investigated, and a convergence study with respect to the coupling constant was carried out for the tilted growth of dendritic arrays with different values of anisotropic to choose proper λ in simulations.
TL;DR: In this paper, the effects of Ce on secondary dendrite arm spacing and mechanical behavior of Al-Si-Cu-Mg alloys were investigated via computer-aided cooling curve thermal analysis.
Abstract: The effects of Ce on the secondary dendrite arm spacing (SDAS) and mechanical behavior of Al–Si–Cu–Mg alloys were investigated. The reduction of SDAS at different Ce concentrations was evaluated in a directional solidification experiment via computer-aided cooling curve thermal analysis (CA‒CCTA). The results showed that 0.1wt%–1.0wt% Ce addition resulted in a rapid solidification time, Δt
s, and low solidification temperature, ΔT
S, whereas 0.1wt% Ce resulted in a fast solidification time, Δt
a–Al, of the α-Al phase. Furthermore, Ce addition refined the SDAS, which was reduced to approximately 36%. The mechanical properties of the alloys with and without Ce were investigated using tensile and hardness tests. The quality index (Q) and ultimate tensile strength of (UTS) Al–Si–Cu–Mg alloys significantly improved with the addition of 0.1wt% Ce. Moreover, the base alloy hardness was improved with increasing Ce concentration.
TL;DR: In this article, a modified Bridgman process (Bridgman seed technique, BST) was used for the production of laboratory Ni-base single crystal (SX) superalloy cylinders of 12/120mm diameter/length.
TL;DR: In this paper, the effect of Ti addition on B removal during silicon refining by directional solidification of Al-30.wt.% Si alloy has been studied, and an apparent segregation coefficient is used to characterize the B removal.
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29 Oct 2017TL;DR: In this article, the effect of a time-periodic vertical gravitational acceleration (or equivalently vibration) on the onset of solutal convection was calculated based on linear stability using Floquet theory.
Abstract: During directional solidification of a binary alloy at constant velocity, thermosolutal convection may occur due to the temperature and solute gradients associated with the solidification process. For vertical growth in an ideal furnace (lacking horizontal gradients) a quiescent state is possible. For a range of processing conditions, the thermal Rayleigh number is sufficiently small that the stabilizing role of the thermal field during growth vertically upwards may be neglected, and only solutal convection need be considered. The effect of a time-periodic vertical gravitational acceleration (or equivalently vibration) on the onset of solutal convection is calculated based on linear stability using Floquet theory. We find that a stable base state can be destabilized due to modulation, while an unstable state can be stabilized. The flow and solute disturbance fields show both synchronous and subharmonic temporal response to the driving sinusoidal modulation.
TL;DR: In this paper, the mass transfer behavior induced by the high frequency magnetic field in a square electromagnetic cold crucible (EMCC) used for directional solidification was experimentally and numerically investigated.
TL;DR: In this article, the microstructural characteristics of steady growth zone, initial growth zone and solid/liquid interface are investigated under high temperature gradient, and the corresponding relationship between growth rate and eutectic spacing is determined.
Abstract: Directionally solidified Al2O3/Er3Al5O12/ZrO2 ternary eutectic ceramic in situ composite rods with length of 110 mm have been fabricated by laser floating zone melting. The microstructural characteristics of steady growth zone, initial growth zone and solid/liquid interface are investigated under high temperature gradient. In the steady growth zone, the eutectic spacing (λ) is rapidly decreased as increasing the growth rate (V), and the corresponding relationship between growth rate and eutectic spacing is determined to be λ = 11.14 × V
−1/2. The temperature gradient has been measured to be about 5.3 × 103 K/cm. In the initial growth zone, the melting process and temperature distribution are recorded by infrared thermal imager, and several unstable complex microstructures are observed. In the quenched zone, the regular eutectics with minimum eutectic spacing of 200 nm are obtained. Moreover, the solid/liquid interface during solidification shows convex interface morphology and the interface height is gradually decreased as increasing the growth rate. The eutectic growth behaviors at the center and edge of the as-grown rod are compared and discussed.