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1
Sobolev, S. L. "Rapid solidification under local nonequilibrium conditions." Physical Review E 55, no. 6 (June 1, 1997): 6845–54. http://dx.doi.org/10.1103/physreve.55.6845.
2
Sobolev, S. L. "Driving force for binary alloy solidification under far from local equilibrium conditions." Acta Materialia 93 (July 2015): 256–63. http://dx.doi.org/10.1016/j.actamat.2015.04.028.
3
Domeij, Björn, and Attila Diószegi. "Solidification Chronology of the Metal Matrix and a Study of Conditions for Micropore Formation in Cast Irons Using EPMA and FTA." Materials Science Forum 925 (June 2018): 436–43. http://dx.doi.org/10.4028/www.scientific.net/msf.925.436.
Анотація:
Microsegregation is intimately coupled with solidification, the development of microstructure, and involved in the formation of various casting defects. This paper demonstrates how the local composition of the metal matrix of graphitic cast irons, measured using quantitative electron microprobe analysis, can be used to determine its solidification chronology. The method is applied in combination with Fourier thermal analysis to investigate the formation of micropores in cast irons with varying proportions of compacted and spheroidal graphite produced by remelting. The results indicate that micropores formed at mass fractions of solid between 0.77 and 0.91, which corresponded to a stage of solidification when the temperature decline of the castings was large and increasing. In 4 out of the 5 castings, pores appear to have formed soon after the rate of solidification and heat dissipation had reached their maximum and were decreasing. While the freezing point depression due to build-up of microsegregation and the transition from compacted to spheroidal type growth of the eutectic both influencing solidification kinetics and the temperature evolution of the casting, the results did not indicate a clear relation to the observed late deceleration of solidification.
4
Sobolev, Sergey L., Mikhail G. Tokmachev, and Yuri R. Kolobov. "Rapid Multicomponent Alloy Solidification with Allowance for the Local Nonequilibrium and Cross-Diffusion Effects." Materials 16, no. 4 (February 15, 2023): 1622. http://dx.doi.org/10.3390/ma16041622.
Анотація:
Motivated by the fast development of various additive manufacturing technologies, we consider a mathematical model of re-solidification of multicomponent metal alloys, which takes place after ultrashort (femtosecond) pulse laser melting of a metal surface. The re-solidification occurs under highly nonequilibrium conditions when solutes diffusion in the bulk liquid cannot be described by the classical diffusion equation of parabolic type (Fick law) but is governed by diffusion equation of hyperbolic type. In addition, the model takes into account diffusive interaction between different solutes (nonzero off-diagonal terms of the diffusion matrix). Numerical simulations demonstrate that there are three main re-solidification regimes, namely, purely diffusion-controlled with solute partition at the interface, partly diffusion-controlled with weak partition, and purely diffusionless and partitionless. The type of the regime governs the final composition of the re-solidified material, and, hence, may serve as one of the main tools to design materials with desirable properties. This implies that the model is expected to be useful in evaluating the most effective re-solidification regime to guide the optimization of additive manufacturing processing parameters and alloys design.
5
Plotkowski, A., K. Fezi, and M. J. M. Krane. "Estimation of transient heat transfer and fluid flow for alloy solidification in a rectangular cavity with an isothermal sidewall." Journal of Fluid Mechanics 779 (August 14, 2015): 53–86. http://dx.doi.org/10.1017/jfm.2015.424.
Анотація:
Transient scaling and integral analyses were performed to predict trends in alloy solidification in a rectangular cavity cooled by an isothermal sidewall. The natural convection fluid flow was approximated by a scaling analysis for a laminar boundary layer at the solidification front, and was coupled to scaling and integral analyses of the energy equation to predict the solidification behaviour of the system. These analyses predicted several relevant aspects of the solidification process, including the time required to extinguish the initial superheat and the maximum local solidification time as a function of the system parameters and material properties. These results were verified by comparison to numerical simulations for an Al–4.5 wt% Cu alloy for various initial and boundary conditions and cavity aspect ratios. The analysis was compared to previous attempts to analyse similar fluid flow and solidification processes, and the limitations of the assumptions used for this analysis were discussed.
6
Gotterbarm, Martin R., Alexander M. Rausch, and Carolin Körner. "Fabrication of Single Crystals through a µ-Helix Grain Selection Process during Electron Beam Metal Additive Manufacturing." Metals 10, no. 3 (February 28, 2020): 313. http://dx.doi.org/10.3390/met10030313.
Анотація:
Selective Electron Beam Melting (SEBM) is a powder bed-based additive manufacturing process for metals. As the electron beam can be moved inertia-free by electromagnetic lenses, the solidification conditions can be deliberately adjusted within the process. This enables control over the local solidification conditions. SEBM typically leads to columnar grain structures. Based on numerical simulation, we demonstrated how technical single crystals develop in IN718 by forcing the temperature gradient along a µ-Helix. The slope of the µ-Helix, i.e., the deviation of the thermal gradient from the build direction, determined the effectiveness of grain selection right up to single crystals.
7
Merchant, G. J., and S. H. Davis. "Kinetic Effects in Directional Solidification." Applied Mechanics Reviews 43, no. 5S (May 1, 1990): S76—S78. http://dx.doi.org/10.1115/1.3120855.
Анотація:
Mullins and Sekerka showed for fixed temperature gradient that the planar interface is linearly stable for all pulling speeds V above some critical value, the absolute stability limit. Near this limit, where solidification rates are rapid, the assumption of local equilibrium at the interface may be violated. We incorporate nonequilibrium effects into a linear stability analysis of the planar front by allowing the segregation coefficient and interface temperature to depend on V in a thermodynamically-consistent way. In addition to the steady cellular mode, we find a new branch of long-wavelength time-periodic states. Under certain conditions there exists a stability window separating the steady and oscillatory branches.
8
Zimmermann, Gerhard, Viktor T. Vitusevych, and Laszlo Sturz. "Microstructure Formation in AlSi6Cu4 Alloy with Forced Melt Flow Induced by a Rotating Magnetic Field." Materials Science Forum 649 (May 2010): 249–54. http://dx.doi.org/10.4028/www.scientific.net/msf.649.249.
Анотація:
The objective of this paper is the experimental investigation of the microstructure in Al-6wt%Si-4wt%Cu alloy, directionally solidified without and with forced melt flow, induced by a rotating magnetic field. The flow leads to reduced primary dendrite spacing and to strong radial segregation of silicon and copper. As a consequence the local solidification conditions change, resulting in different types of Al2Cu phase formation. This outcome is explained by ThermoCalc calculations predicting the corresponding solidification behavior.
9
Heckmann, C. J., W. Stets, and G. Wolf. "Plate Fracture of Nodular Cast Iron." Key Engineering Materials 457 (December 2010): 367–73. http://dx.doi.org/10.4028/www.scientific.net/kem.457.367.
Анотація:
Plate fracture is a defective fracture structure in nodular cast iron that can be found especially in the transition area of feeder, feeder neck and the cast part itself. It occurs rather spontaneously due to the fact that the exact reason for it is still unknown. The microstructure of the casting in the area of plate fracture comprises aligned graphite nodules in combination with a pronounced dendritic microstructure as characteristical features. A series of casting trials was performed in which plate like samples were produced. It could be shown by means of metallographic investigation of these samples in combination with the simulation of the solidification that specific local conditions during the solidification are the metallurgical reasons for the appearance of plate fracture. These specific conditions were the local temperature gradient and the velocity of the liquid/solid interface.
10
Huo, Miao, Chuyue Chen, Hangyue Jian, Wenchao Yang, and Lin Liu. "The Stray Grains from Fragments in the Rejoined Platforms of Ni-Based Single-Crystal Superalloy." Metals 13, no. 8 (August 15, 2023): 1470. http://dx.doi.org/10.3390/met13081470.
Анотація:
Nickel-based single crystal superalloy is the most important material for blade preparation. However, some solidification defects inevitably occur during the process of preparing single-crystal blades through directional solidification. In this study, in order to study the origin of misorientation defects during solidification, a model with rejoined platforms was designed according to the geometry of single-crystal guide vanes. Electron Back-Scattering Diffraction (EBSD) was used to quantify the orientation deviation of the dendrites and identify the solidification defects in the rejoined platforms. The results showed that stray grain defects appeared in the platforms and their misorientation changed gradually, not abruptly. Combined with the simulation results, it was proposed that the stray grains formed as the result of the dendrites fragment, which was induced by solute enrichment in the mushy zone during solidification. Meanwhile, it was accompanied by a obvious dendritic deformation, which was caused by solidification shrinkage stress. This suggested that the fragmentation was induced by multiple factors, among which, the concave interface shape provided favorable conditions for solute enrichment, and the dynamic variability in the local thermal gradient and fluctuations of the solidification rate might play catalytic roles.
11
Rittinghaus, Silja-Katharina, and Jonas Zielinski. "Influence of Process Conditions on the Local Solidification and Microstructure During Laser Metal Deposition of an Intermetallic TiAl Alloy (GE4822)." Metallurgical and Materials Transactions A 52, no. 3 (February 4, 2021): 1106–16. http://dx.doi.org/10.1007/s11661-021-06139-2.
Анотація:
AbstractTemperature-time cycles are essential for the formation of microstructures and thus the mechanical properties of materials. In additive manufacturing, components undergo changing temperature regimes because of the track- and layer-wise build-up. Because of the high brittleness of titanium aluminides, preheating is used to prevent cracking. This also effects the thermal history. In the present study, local solidification conditions during the additive manufacturing process of Ti-48Al-2Cr-2Nb with laser metal deposition (LMD) are investigated by both simulation and experimental investigations. Dependencies of the build-up height, preheating temperatures, process parameters and effects on the resulting microstructure are considered, including the heat treatment. Solidification conditions are found to be dependent on the build height and thus actual preheating temperature, process parameters and location in the melt pool. Influences on both chemical composition and microstructure are observed. Resulting differences can almost be balanced through post heat treatment.
12
PLOTKOWSKI, ALEX. "Geometry-Dependent Solidification Regimes in Metal Additive Manufacturing." Welding Journal 99, no. 2 (February 1, 2020): 59s—66s. http://dx.doi.org/10.29391/2020.99.006.
Анотація:
Recent modeling and experimental work in additive manufacturing has suggested cross-sectional geometry may play a significant role in the local development of the solidification structure through its influence on the heat source path. This effect has been rationalized as the transi-tion from a quasistatic point heat source regime to a regime dominated by the quasistatic motion of an equiva-lent line source. This work provides a simple analytical framework for determining the conditions under which a system transitions between these regimes. A transient semianalytical heat transfer model is used to examine a wide range of process conditions and material properties. A simple analytical expression is derived and shown to accu-rately predict the transition between solidification regimes over these conditions. The functional form of this expres-sion is then used to help understand the importance of various material properties, process parameters, and geometric factors on the characteristics of the solidification con-ditions. This approach may be used as a simple guideline for optimizing process conditions in response to variations in cross-sectional geometry to produce more consistent microstructural distributions in additively manufactured components.
13
Cenni, Riccardo, Matteo Cova, and Giacomo Bertuzzi. "A methodology to consider local material properties in structural optimization." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 231, no. 15 (March 29, 2016): 2822–34. http://dx.doi.org/10.1177/0954406216640807.
Анотація:
We propose a finite element methodology to consider local material properties for large cast iron components in shape optimization. We found that considering local strength instead of uniform strength within shape optimization brings to different results in terms of safety-cost balance for the same component. It is well known that local mechanical properties of large cast iron components are defined by their microstructure and defects, which locally affect the strength of the components. Considering or not local mechanical properties can dramatically change a component reliability evaluation during its design. Since a typical industrial aim for shape optimization is trying to get the optimal solution in terms of component quality and cost, considering local material properties is even more important than in traditional design process where no optimization techniques are used. We compute solidification process parameters via finite element solidification analysis, and then we exploit experimental correlation between these parameters and ultimate tensile strength to evaluate the local reliability of the finished component under its static loading conditions. We believe that this methodology represents an opportunity to better design casting components when mechanical properties are deeply affected by their production process as described in the provided examples. In these examples, we wanted to minimize casting cost constrained by a target reliability and we get component cost reduction by considering local material properties. Future research will address the problem of using dedicated casting simulation software instead of general purpose finite element analysis software to compute solidification analysis and then introducing fatigue analysis and correlation between fatigue material properties and casting process output variables.
14
Basu, I., J. T. Wood, and Jonathan P. Weiler. "Effect of Process Variables on Microstructural Features during Solidification of AM60B Magnesium Alloy." Materials Science Forum 706-709 (January 2012): 1279–84. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.1279.
Анотація:
In this study, commercial AM60B magnesium alloy was studied under different solidification conditions to understand the influence of cooling rate, thermal gradient, growth velocity, Niyama criterion, solidification time and mold dimensions on microstructural features such as secondary and tertiary dendrite arm spacing, grain size, porosity, pore shape and size, local morphological and phase variations. Porosity, grain size and dendrite arm spacing were measured as functions of the process variables. It was realized that the process of mold filling and solidification are simultaneous in nature and they significantly affect the microstructure development trends and its dependency on the process parameters. A significant effect, of the above mentioned, was found on the obtained porosity values and their variation along the casting. The results clearly indicate that rate of filling, nature of flow of liquid and shape of the mold greatly affect the solidification process and thereby the microstructure.
15
Rodrigues, Christian M. G., Menghuai Wu, Haijie Zhang, Andreas Ludwig, and Abdellah Kharicha. "Bridging Capillary-Driven Fragmentation and Grain Transport with Mixed Columnar-Equiaxed Solidification." Metallurgical and Materials Transactions A 52, no. 10 (August 12, 2021): 4609–22. http://dx.doi.org/10.1007/s11661-021-06414-2.
Анотація:
AbstractIn this study, a first attempt is made to bridge capillary-driven fragmentation and grain transport using a mixed columnar-equiaxed solidification model. Grain transport is an intrinsic feature of the employed solidification model which has been extensively investigated over the years. Regarding the capillary-driven fragmentation event, a new correlation between the number of fragments and interfacial area density of the columnar structure was recently established by Cool and Voorhees (2017) based on experimental research under isothermal conditions. Here, we propose to modify Cool and Voorhees’ equation to extend its range of applicability to the solidification-dominant stage without destroying the agreement with the reported measurements in the coarsening-dominant stage. With this improvement in the mixed columnar-equiaxed solidification model, capillary effects can be isolated from the motion of the phases during fragmentation events, which facilitates understanding of the results. Under pure diffusive solidification conditions (no flow or crystal sedimentation), the simulation results were validated against phase-field simulations. In more realistic scenarios where liquid flow and fragment sedimentation are both considered, the simulations indicate very reasonable results for the detection of columnar-to-equiaxed transition, which suggests that the newly proposed model can be an important tool for industrial casting applications. Moreover, flow direction and intensity were shown to affect the potential for local fragmentation. Graphic Abstract
16
Roósz, András, Arnold Rónaföldi, Yuze Li, Nathalie Mangelinck-Noël, Gerhard Zimmermann, Henri Nguyen-Thi, Mária Svéda, and Zsolt Veres. "Microstructure Analysis of Al-7 wt% Si Alloy Solidified on Earth Compared to Similar Experiments in Microgravity." Crystals 12, no. 9 (August 31, 2022): 1226. http://dx.doi.org/10.3390/cryst12091226.
Анотація:
During ground-based solidification, buoyancy flow can develop by the density difference in the hypoeutectic type of the alloys, such as Al-7 wt% Si alloy. Buoyancy flow can affect the thermal field, solute distribution in the melt, and the position and amount of the new grains. As solidification is a very complex process, it is not very easy to separate the different effects. Under microgravity conditions, natural convection does not exist or is strongly damped due to the absence of the buoyancy force. Therefore, experiments in microgravity conditions provide unique benchmark data for pure diffusive solidification conditions. Compared to the results of the ground-based and microgravity experiments, it is possible to get information on the effect of gravity (buoyancy force). In the framework of the CETSOL project, four microgravity solidification experiments were performed on grain refined (GF) and non-grain refined Al-7 wt% Si alloy onboard the International Space Station in the Materials Science Laboratory. These experiments aimed to study the effect of the solidification parameters (solid/liquid front velocity vSL, temperature gradient GSL) on the grain structure and dendritic microstructures. The microgravity environment eliminates the melt flow, which develops on Earth due to gravity. Four ground-based (GB) experiments were performed under Earth-like conditions with the same (similar) solidification parameters in a vertical Bridgman-type furnace having four heating zones. The detailed analysis of the grain structure, amount of eutectic, and secondary dendrite arm spacing (SDAS) for different process conditions is reported and compared with the results of the microgravity experiments. GB experiments showed that the microstructure was columnar in the samples that do not contain GF material or in case the solid/liquid (vSL front velocity was slow (0.02 mm/s)). In contrast, in the sample which contained GF material, progressive columnar/equiaxed transition (PCET) was observed at vSL = 0.077 mm/s and GSL = 3.9 K/mm. The secondary (SDAS) dendrite arm spacing follows the well-known power law, SDAS=K[t0]13, where K is a constant, and t0 is the local solidification time for both GB and µg experiments.
17
Atkinson, Helen V., Faraj Alshmri, S. V. Hainsworth, and S. D. A. Lawes. "Microstructural Characterization of Rapidly Solidified Al-High Si Alloys." Advanced Materials Research 328-330 (September 2011): 1545–51. http://dx.doi.org/10.4028/www.scientific.net/amr.328-330.1545.
Анотація:
Aluminium silicon alloys are the most used raw material for automotive applications. One of the main limitations on using aluminium high silicon alloys is the formation of coarse brittle phases under conventional solidification conditions. However, rapid solidification processing (RS) (for example, through melt spinning) is very effective in limiting the coarsening of primary silicon due to the high cooling rate. In the present work, characterisation of the material at the first stage of production as melt-spun ribbon and flake has been carried out. The microstructures show typical characteristics of a ‘featureless zone’ on the wheel-side and coarser microstructures on the air-side, with clusters of silicon particles evident. At high magnification, on the wheel-side, TEM and FEGSEM reveal local variations in the silicon and aluminium content (although on average there is no macrosegregation from the wheel-side to the air-side during solidification). In FEGSEM, the ‘rosette-structure’ also displays local variations in Al, Si, Fe, Cu and Ni over a scale of a few microns.
18
Hagenlocher, Christian, Patrick O’Toole, Wei Xu, Milan Brandt, Mark Easton, and Andrey Molotnikov. "The Effect of Heat Accumulation on the Local Grain Structure in Laser-Directed Energy Deposition of Aluminium." Metals 12, no. 10 (September 25, 2022): 1601. http://dx.doi.org/10.3390/met12101601.
Анотація:
The energy used to melt the material at each layer during laser-directed energy deposition (L-DED) accumulates in the solidified layers upon layer deposition and leads to an increase in the temperature of the part with an increasing number of layers. This heat accumulation can lead to inhomogeneous solidification conditions, increasing residual stresses and potentially anisotropic mechanical properties due to columnar grain structures. In this work, infrared imaging is applied during the directed energy deposition process to capture the evolution of the temperature field in high spatial and temporal evolutions. Image processing algorithms determined the solidification rate and the temperature gradient in the spatial and temporal evolutions and evidenced their change with the proceeding deposition process. Metallographic analysis proves that these changes significantly affect the local grain structure of the L-DED fabricated parts. The study provides comprehensive quantitative measurements of the change in the solidification variables in local and temporal resolutions. The comprehensive comparison of different parameter combinations reveals that applied power, and especially the frequency of the consecutive deposition of the individual layers, are the key parameters to adjusting heat accumulation. These findings provide a methodology for optimising L-DED manufacturing processes and tailoring the local microstructure development by controlling heat accumulation.
19
Rohatgi, P. K., K. Pasciak, C. S. Narendranath, S. Ray, and A. Sachdev. "Evolution of microstructure and local thermal conditions during directional solidification of A356-SiC particle composites." Journal of Materials Science 29, no. 20 (1994): 5357–66. http://dx.doi.org/10.1007/bf01171548.
20
Tiedje, Niels S., Mathias K. Bjerre, Mohammed A. Azeem, Jesper H. Hattel, and Peter D. Lee. "Analysis of Local Conditions on Graphite Growth and Shape During Solidification of Ductile Cast Iron." Transactions of the Indian Institute of Metals 71, no. 11 (October 28, 2018): 2699–705. http://dx.doi.org/10.1007/s12666-018-1448-z.
21
Zhou, B., M. Apel, J. Eiken, R. Berger, S. Gor, and N. Wolff. "Influence of cooling path on solidification morphology and hot tearing susceptibility of an Al−Cu−Fe−Mg−Si alloy." Materialwissenschaft und Werkstofftechnik 55, no. 1 (January 2024): 53–61. http://dx.doi.org/10.1002/mawe.202300167.
Анотація:
AbstractIn this work, a numerical approach is applied to study the impact of local cooling conditions on the hot tearing in an aluminium‐copper alloy with iron, magnesium and silicon as impurities. At first, CALPHAD‐coupled multicomponent and multiphase‐field simulations were performed to elucidate the effect of cooling conditions on solidification morphology in the final, critical stage of solidification. Then, the evolution of the melt flow permeability is derived from the simulated three‐dimensional microstructures and discussed in the context of the Rappaz‐Drezet‐Gremaud criterion for hot tearing susceptibility. With increasing cooling rates, the microstructure becomes finer and the resulting permeability first increases and then saturates within the investigated range. It is shown that the Rappaz‐Drezet‐Gremaud hot‐tearing criterion in combination with microstructure simulations responds to different cooling conditions in contrast to a Scheil‐Gulliver based model or an evaluation of the average Kou‐index.
22
Drezet, Jean Marie, and Sélim Mokadem. "Marangoni Convection and Fragmentation in LASER Treatment." Materials Science Forum 508 (March 2006): 257–62. http://dx.doi.org/10.4028/www.scientific.net/msf.508.257.
Анотація:
Epitaxial Laser Metal Forming (E-LMF) consists in impinging a jet of metallic powder onto a molten pool formed by controlled laser heating and thereby, generating epitaxially a single crystal deposit onto a single crystal substrate. It is a near net-shape process for rapid prototyping or repair engineering of single crystal high pressure/high temperature gas turbines blades. Single crystal repair using E-LMF requires controlled solidification conditions in order to prevent the nucleation and growth of crystals ahead of the columnar dendritic front, i.e., to ensure epitaxial growth and to avoid the columnar to equiaxed transition. A major limitation to the process lies in the formation of stray grains which can originate either from heterogeneous nucleation ahead of the solidification front or from remelting of dendrite arms due to local solute enriched liquid flow, .i.e fragmentation. To study this last aspect, heat and fluid flow modelling is required to establish the relationship between process parameters such as laser power, beam diameter and scanning speed, and the local solidification conditions plus the fluid flow in the vicinity of the mushy zone. Surface tension driven convection known as the Marangoni effect needs to be included in the model owing to its large influence on the development of eddies and on the shape of the liquid pool. The 3D model implemented in the FE software calcosoft® is used to compute the fluid convection within the liquid pool and to assess the risk of fragmentation using a criterion based on the local velocity field and thermal gradient. The computed results are compared with EBSD maps of laser traces carried out at EPF-Lausanne in re-melting experiments.
23
Schaar, Helge, Ingo Steinbach, and Marvin Tegeler. "Numerical Study of Epitaxial Growth after Partial Remelting during Selective Electron Beam Melting in the Context of Ni–Al." Metals 11, no. 12 (December 13, 2021): 2012. http://dx.doi.org/10.3390/met11122012.
Анотація:
In the selective electron beam melting approach an electron beam is used to partially melt the material powder. Based on the local high energy input, the solidification conditions and likewise the microstructures strongly deviate from conventional investment casting processes. The repeated energy input into the material during processing leads to the partial remelting of the already existing microstructure. To closer investigative this effect of partial remelting, in the present work the phase-field model is applied. In the first part the solidification of the referenced Ni–Al system is simulated in respect to selective electron beam melting. The model is calibrated such to reproduce the solidification kinetics of the superalloy CMSX-4. By comparison to experimental observations reported in the literature, the model is validated and is subsequently applied to study the effect of partial remelting. In the numerical approach the microstructures obtained from the solidification simulations are taken as starting condition. By systematically varying the temperature of the liquid built layer, the effect of remelting on the existing microstructure can be investigated. Based on these results, the experimental processing can be optimized further to produce parts with significantly more homogenous element distributions.
24
Bondareva, Nadezhda S., and Mikhail A. Sheremet. "Numerical Simulation of Melting of Phase Change Material in a Square Cavity with a Heat Source." Key Engineering Materials 685 (February 2016): 104–8. http://dx.doi.org/10.4028/www.scientific.net/kem.685.104.
Анотація:
Melting and solidification problems are important in applications of many industries. In the present work mathematical simulation of natural convection with phase transition inside an enclosure with a local heat source has been carried out. Partial differential equations with corresponding initial and boundary conditions have been solved using the finite difference method. The effect of temperature differences on fluid flow and heat transfer has been discussed.
25
Mochnacki, Bohdan, and Ewa Majchrzak. "Numerical Modeling of Casting Solidification Using Generalized Finite Difference Method." Materials Science Forum 638-642 (January 2010): 2676–81. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.2676.
Анотація:
The system casting-mould is considered. The thermal processes proceeding in a casting sub-domain are described using the one domain approach. The model of solidification process is supplemented by the energy equation concerning the mould sub-domain, the continuity conditions given on the contact surface between casting and mould, boundary conditions on the outer surface of the system and the initial ones. To solve the problem the generalized variant of finite difference method (GFDM) is used. Temporary and local values of temperature can be found at the optional set of collocation points from the domain considered. This essential advantage of GFDM allows to locate and thicken nodes at the regions for which the temperature gradients and cooling (heating) rates are considerable. In the final part of the paper, the example of numerical simulation is shown.
26
Rausch, Alexander M., Martin R. Gotterbarm, Julian Pistor, Matthias Markl, and Carolin Körner. "New Grain Formation by Constitutional Undercooling Due to Remelting of Segregated Microstructures during Powder Bed Fusion." Materials 13, no. 23 (December 3, 2020): 5517. http://dx.doi.org/10.3390/ma13235517.
Анотація:
A microstructure has significant influence on the mechanical properties of parts. For isotropic properties, the formation of equiaxed microstructures by the nucleation of new grains during solidification is necessary. For conventional solidification processes, nucleation is well-understood. Regarding powder bed fusion, the repeated remelting of previous layers can cause nucleation under some conditions that are not explainable with classical theories. Here, we investigate this nucleation mechanism with an unprecedented level of detail. In the first step, we built samples with single crystalline microstructures from Ni-base superalloy IN718 by selective electron beam melting. In the second step, single lines with different parameters were molten on top of these samples. We observed a huge number of new grains by nucleation at the melt-pool border of these single lines. However, new grains can only prevail if the alignment of their crystallographic orientation with respect to the local temperature gradient is superior to that of the base material. The current hypothesis is that nucleation at the melt-pool border happens due to remelting microsegregations from former solidification processes leading to constitutional undercooling directly at the onset of solidification. This study offers the opportunity to understand and exploit this mechanism for different manufacturing processes.
27
Klinkhammer, J., J. Thorborg, M. Bernhard, J. Winkler, C. Bernhard, R. Hanus, and G. Tischler. "Hot tear prediction in large sized high alloyed turbine steel parts - experimental based calibration of mechanical data and model validation." IOP Conference Series: Materials Science and Engineering 1281, no. 1 (May 1, 2023): 012068. http://dx.doi.org/10.1088/1757-899x/1281/1/012068.
Анотація:
Abstract The main defects in heavy steel castings are related to hot tear formation during solidification. Depending on the steel grade, design, and local solidification conditions, it is possible to predict regions with higher risk of hot tear formation during the casting process. However, steels containing Boron show more complex crack and defect patterns compared to common steel casting alloys. The mechanisms behind the Boron induced hot tearing is investigated in this work to understand the influence of Boron enrichment during solidification and the influence on hot tearing. The experimental work includes the investigation of phase diagrams and the corresponding fractions of the solid and liquid phases depending on temperature using thermal analysis e.g. DSC and HT-LSCM. The hot tearing sensitivity and mechanical properties during solidification are obtained in the Submerged Split Chill Test, SSCT. In addition IMC-B 3-point bending tests are performed to determine high-temperature material properties in the solid state. The work is part of a research project where the final goal is to improve the hot tear predictions based on experimental work and carry out a benchmark simulation of a real sized casting and use it to show the agreement between the numerical results and extensive non-destructive testing from industrial observations.
28
Khaimovich, Alexander, Igor Shishkovsky, Yaroslav Erisov, Anton Agapovichev, Vitaliy Smelov, and Vasilii Razzhivin. "Research on Cracked Conditions in Nickel Chrome Alloy Ni50Cr33W4.5Mo2.8TiAlNb, Obtained by Direct Laser Deposition." Metals 12, no. 11 (November 7, 2022): 1902. http://dx.doi.org/10.3390/met12111902.
Анотація:
Nowadays, additive manufacturing (AM) is a powerful way to make complex-shaped components for airspace engineering from nickel-based superalloys. So, while nickel-based superalloys could easily be we L-DED in sheet-metal thicknesses, they suffered from strain-age cracking and solidification during AM or in the post-weld aging treatment. This is attributed to the fact that besides the limitation of γ′- phase forming elements (Al and Ti), as they form by AM very rapidly and reduce ductility, the majority of the superalloys contain carbide-forming elements such as Cr, Mo, and W. The precipitation of carbides, which is very effective in strengthening, develops cracks in the heat-affected zone (HAZ) during AM. The difference in isochoric heat capacities and the thermal expansion coefficient (TEC) at the phase boundary leads to the appearance of dangerous local destruction energy. If the area of the interfacial interface is sufficiently extended, then the accumulation of this energy reaches a level sufficient for a crack formation. We have proposed a crack initiation criterion (CIC) for assessing the dangerous level of fracture energy. The CIC was derived from an estimate of the local energy balance from the heat transfer equation for the two-phase area. Practical approbation of the criterion was carried out after L-DED of samples from Ni50Cr33W4.5Mo2.8TiAlNb (EP648) alloy powder with an increased carbon content based on the study of the chemical composition near the crack formed during solidification. Using the proposed criterion provides an opportunity to give the rank to carbide-forming elements according to the degree of their influence on the fracture energy. Thus, the release of aluminum carbide turned out to be 5.48 times more dangerous than the release of titanium carbide and more than 5 times more dangerous than the release of tungsten carbide and molybdenum.
29
Skrzypczak, T., E. Węgrzyn-Skrzypczak, and J. Winczek. "Effect Of Natural Convection On Directional Solidification Of Pure Metal." Archives of Metallurgy and Materials 60, no. 2 (June 1, 2015): 835–41. http://dx.doi.org/10.1515/amm-2015-0215.
Анотація:
AbstractThe paper is focused on the modeling of the directional solidification process of pure metal. During the process the solidification front is sharp in the shape of the surface separating liquid from solid in three dimensional space or a curve in 2D. The position and shape of the solid-liquid interface change according to time. The local velocity of the interface depends on the values of heat fluxes on the solid and liquid sides. Sharp interface solidification belongs to the phase transition problems which occur due to temperature changes, pressure, etc. Transition from one state to another is discontinuous from the mathematical point of view. Such process can be identified during water freezing, evaporation, melting and solidification of metals and alloys, etc.The influence of natural convection on the temperature distribution and the solid-liquid interface motion during solidification of pure copper is studied. The mathematical model of the process is based on the differential equations of heat transfer with convection, Navier-Stokes equation and the motion of the interface. This system of equations is supplemented by the appropriate initial and boundary conditions. In addition the continuity conditions at the solidification interface must be properly formulated. The solution involves the determination of the temporary temperature and velocity fields and the position of the interface. Typically, it is impossible to obtain the exact solution of such problem. The numerical model of solidification of pure copper in a closed cavity is presented, the influence of the natural convection on the phase change is investigated. Mathematical formulation of the problem is based on the Stefan problem with moving internal boundaries. The equations are spatially discretized with the use of fixed grid by means of the Finite Element Method (FEM). Front advancing technique uses the Level Set Method (LSM). Chorin’s projection method is used to solve Navier-Stokes equation. Such approach makes possible to uncouple velocities and pressure. The Petrov-Galerkin formulation is employed to stabilize numerical solutions of the equations. The results of numerical simulations in the 2D region are discussed and compared to the results obtained from the simulation where movement of the liquid phase was neglected.
30
Galenko, Peter K., Dmitri V. Alexandrov, and Ekaterina A. Titova. "The boundary integral theory for slow and rapid curved solid/liquid interfaces propagating into binary systems." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 376, no. 2113 (January 8, 2018): 20170218. http://dx.doi.org/10.1098/rsta.2017.0218.
Анотація:
The boundary integral method for propagating solid/liquid interfaces is detailed with allowance for the thermo-solutal Stefan-type models. Two types of mass transfer mechanisms corresponding to the local equilibrium (parabolic-type equation) and local non-equilibrium (hyperbolic-type equation) solidification conditions are considered. A unified integro-differential equation for the curved interface is derived. This equation contains the steady-state conditions of solidification as a special case. The boundary integral analysis demonstrates how to derive the quasi-stationary Ivantsov and Horvay–Cahn solutions that, respectively, define the paraboloidal and elliptical crystal shapes. In the limit of highest Péclet numbers, these quasi-stationary solutions describe the shape of the area around the dendritic tip in the form of a smooth sphere in the isotropic case and a deformed sphere along the directions of anisotropy strength in the anisotropic case. A thermo-solutal selection criterion of the quasi-stationary growth mode of dendrites which includes arbitrary Péclet numbers is obtained. To demonstrate the selection of patterns, computational modelling of the quasi-stationary growth of crystals in a binary mixture is carried out. The modelling makes it possible to obtain selected structures in the form of dendritic, fractal or planar crystals. This article is part of the theme issue ‘From atomistic interfaces to dendritic patterns’.
31
Li, Yang, Pei Jia Li, Xing Fu Chen, Hao Ran Liu, Jian Tao Wu, and Jun Tao Li. "Investment Casting Defects of a Turbine Nozzle Made by K465 Alloy." Materials Science Forum 898 (June 2017): 487–91. http://dx.doi.org/10.4028/www.scientific.net/msf.898.487.
Анотація:
The investment casting defects in a turbine nozzle with size of φ 331mm and thickness 0.7 mm and the number of vanes of 31 have been studied in two aspects, which were the porosity of the turbine nozzle’s inner cone and the cracks of the turbine nozzle’s vanes. ProCAST software was used to analyze the nozzle’s solidification process. A suitable gating system was used to solve porosity issues effectively by changing local thickness and improving solidification conditions. The crack on the nozzle’s vanes was studied and a kind of grain refiner was used to solve crack issues by improving shell strength. In order to manufacture castings with high metallurgical quality and meet the design and use demands, a reasonable gating system and a moderate shell process were used.
32
Keary, A. C., and R. J. Bowen. "On the Prediction of Local Ice Formation in Pipes in the Presence of Natural Convection." Journal of Heat Transfer 121, no. 4 (November 1, 1999): 934–44. http://dx.doi.org/10.1115/1.2826084.
Анотація:
Pipe freezing is a pipeline maintenance technique which is used to isolate sections of a liquid-filled pipeline by freezing the contents to form a solid pressure-resistant plug. This paper describes the development of a numerical model of natural convection and solidification in a vertical water-filled pipe. The natural convection-driven flows are examined in detail and the interaction with the forming ice plug is studied. The results are compared with experimental data. The numerical approach is contrasted with a simpler one-dimensional analytical method and criteria are proposed to aid the choice of modeling technique under different conditions.
33
Drezet, J. M., S. Pellerin, C. Bezençon, and S. Mokadem. "Modelling the Marangoni convection in laser heat treatment." Journal de Physique IV 120 (December 2004): 299–306. http://dx.doi.org/10.1051/jp4:2004120034.
Анотація:
Epitaxial Laser Metal Forming (E-LMF) consists in impinging a jet of metallic powder onto a molten pool formed by controlled laser heating and thereby, generating epitaxially a single crystal deposit onto the damaged component. This new technique aims to be used for the repair and reshape single crystal gas turbine components. Because of the very localised melting pool, the high temperature gradients produced during the process must be carefully controlled in order to avoid both the columnar-to-equiaxed transition (CET) and the appearance of hot tears. To this end, heat flow modelling is required to establish the relationship between process parameters such as laser power, beam diameter and scanning speed, and the local solidification conditions. When modelling the heat transfer within the sample, it is necessary to include the liquid flow pattern generated by the surface tension driven convection known as the Marangoni effect. Indeed, the fluid flow in the liquid pool dictates the shape of the traces as shown by the measurements carried out at EPF-Lausanne in re-melting experiments. A three dimensional (3D) model is implemented in the finite element software calcosoft$^\text{\textregistered}$ in order to model the development of the fluid convection within the liquid pool. It is shown that the velocities due to natural convection are of the order of 1 mm/sec whereas Marangoni convection produces velocities of the order of 1 m/sec. Moreover, at low scanning speeds, the liquid pool becomes larger than the beam diameter and the development of Marangoni eddies leads to a widening and deepening of the pool. The local solidification conditions such as the thermal gradient and the solidification speed can be extracted at both the solidus and liquidus temperatures to assess the risk of CET and hot cracking.
34
O'Donnell, Robert G., Dayalan R. Gunasegaram, and Michel Givord. "Die Casting Improvements through Melt Shear." Materials Science Forum 618-619 (April 2009): 33–37. http://dx.doi.org/10.4028/www.scientific.net/msf.618-619.33.
Анотація:
Melt flow and solidification within a die casting cavity is a complex process dependent in part on melt pressure (with or without intensification), melt velocity, melt flow path, thermal gradients within the die, die lubrication and melt viscosity. Casting defects such as short shots, cold shuts and shrinkage porosity can readily occur if casting conditions are not optimised. Shrinkage porosity in particular is difficult to eradicate from castings that comprise thick sections, since these sections will usually solidify late in the casting cycle and may be starved of melt supply during the critical solidification (and contraction) stage. The current work seeks to elucidate the influence of the melt shearing on the die casting process and demonstrates that the modifications made to the melt through introduction of a local constriction in the melt path can generate improvements in casting microstructure and reduce shrinkage porosity.
35
Tiedje, Niels Skat, Jesper Henri Hattel, John A. Taylor, and Mark A. Easton. "Modelling Eutectic Growth in Unmodified and Modified Near-Eutectic Al-Si Alloy." Materials Science Forum 765 (July 2013): 160–64. http://dx.doi.org/10.4028/www.scientific.net/msf.765.160.
Анотація:
A numerical model that describes solidification of primary aluminium grains and nucleation and growth of eutectic cells is used to analyse the solidification of an Al-12.5wt% Si alloy. Nucleation of eutectic cells is modelled using an Oldfield-type nucleation model where the number of nuclei in the melt is determined by the amount of active nuclei and the local undercooling from the surface to the centre of a plate casting. Eutectic grains are modelled as spheres growing between the dendrites. The growth velocity of the eutectic cells is a function of undercooling. Experimentally determined growth parameters from the literature that depend on the type of modification (unmodified, Na-modified or Sr-modified) are used to describe differences in growth of the alloys. Modelling results are compared with solidification experiments where an Al-12.5wt%Si alloy was cast in unmodified, Na modified and Sr modified forms. The model confirms experimental observations of how modification and alloy composition influence nucleation, growth and finally the size of eutectic cells in the alloys. Modelling results are used to explain how cooling conditions in the casting act together with the nuclei density in the liquid and the growth velocity of the eutectic cells to determine the size and distribution of eutectic cells in the solidified material.
36
Zyska, Andrzej. "CA Modeling of Microsegregation and Growth of Equiaxed Dendrites in the Binary Al-Mg Alloy." Materials 14, no. 12 (June 18, 2021): 3393. http://dx.doi.org/10.3390/ma14123393.
Анотація:
A two-dimensional model based on the Cellular Automaton (CA) technique for simulating free dendritic growth in the binary Al + 5 wt.% alloy was presented. In the model, the local increment of the solid fraction was calculated using a methodology that takes into account changes in the concentration of the liquid and solid phase component in the interface cells during the solidification transition. The procedure of discarding the alloy component to the cells in the immediate vicinity was used to describe the initial, unstable dendrite growth phase under transient diffusion conditions. Numerical simulations of solidification were performed for a single dendrite using cooling rates of 5, 25 and 45 K/s and for many crystals assuming the boundary condition of the third kind (Newton). The formation and growth of primary and secondary branches as well as the development of component microsegregation in the liquid and solid phase during solidification of the investigated alloy were analysed. It was found that with an increase in the cooling rate, the dendrite morphology changes, its cross-section and the distance between the secondary arms decrease, while the degree of component microsegregation and temperature recalescence in the initial stage of solidification increase. In order to determine the potential of the numerical model, the simulation results were compared with the predictions of the Lipton–Glicksman–Kurz (LGK) analytical model and the experimental solidification tests. It was demonstrated that the variability of the dendrite tip diameter and the growth rate determined in the Cellular Automaton (CA) model are similar to the values obtained in the LGK model. As part of the solidification tests carried out using the Derivative Differential Thermal Analysis (DDTA) method, a good fit of the CA model was established in terms of the shape of the solidification curves as well as the location of the characteristic phase transition temperatures and transformation time. Comparative tests of the real structure of the Al + 5 wt.% Mg alloy with the simulated structure were also carried out, and the compliance of the Secondary Dendrite Arm Spacing (SDAS) parameter and magnesium concentration profiles on the cross-section of the secondary dendrites arms was assessed.
37
Bi, Zhijie, and Xiangxin Guo. "Solidification for solid-state lithium batteries with high energy density and long cycle life." Energy Materials 2, no. 2 (2022): 200011. http://dx.doi.org/10.20517/energymater.2022.07.
Анотація:
Conventional lithium-ion batteries with inflammable organic liquid electrolytes are required to make a breakthrough regarding their bottlenecks of energy density and safety, as demanded by the ever-increasing development of electric vehicles and grids. In this context, solid-state lithium batteries (SSLBs), which replace liquid electrolytes with solid counterparts, have become a popular research topic due to their excellent potential in the realization of improved energy density and safety. However, in practice, the energy density of SSLBs is limited by the cathode mass loading, electrolyte thickness and anode stability. Moreover, the crucial interfacial issues related to the rigid and heterogeneous solid-solid contacts between the electrolytes and electrodes, including inhomogeneous local potential distributions, sluggish ion transport, side reactions, space charge barriers and stability degradation, severely deteriorate the cycle life of SSLBs. Solidification, which converts a liquid into a solid inside a solid battery, represents a powerful tool to overcome the aforementioned obstacles. The liquid precursors fully wet the interfaces and infiltrate the electrodes, followed by in-situ conformal solidification under certain conditions for the all-in-one construction of cells with highly conducting, closely contacted and sustainable electrode/electrolyte interfaces, thereby enabling high energy density and long cycle life. Therefore, in this review, we address the research progress regarding the latest strategies toward the solidification of the electrolyte layers and the interfaces between the electrodes and electrolytes. The critical challenges and future research directions are proposed for the solidification strategies in SSLBs from both science and engineering perspectives.
38
Liu, Heping, Jianjun Zhang, Hongbiao Tao, and Hui Zhang. "Numerical analysis of local heat flux and thin-slab solidification in a CSP funnel-type mold with electromagnetic braking." Metallurgical Research & Technology 117, no. 6 (2020): 602. http://dx.doi.org/10.1051/metal/2020044.
Анотація:
In this article, based on the actual monitored temperature data from mold copper plate with a dense thermocouple layout and the measured magnetic flux density values in a CSP thin-slab mold, the local heat flux and thin-slab solidification features in the funnel-type mold with electromagnetic braking are analyzed. The differences of local heat flux, fluid flow and solidified shell growth features between two steel grades of Q235B with carbon content of 0.19%C and DC01 of 0.03%C under varying operation conditions are discussed. The results show the maximum transverse local heat flux is near the meniscus region of over 0.3 m away from the center of the wide face, which corresponds to the upper flow circulation and the large turbulent kinetic energy in a CSP funnel-type mold. The increased slab width and low casting speed can reduce the fluctuation of the transverse local heat flux near the meniscus. There is a decreased transverse local heat flux in the center of the wide face after the solidified shell is pulled through the transition zone from the funnel-curve to the parallel-cure zone. In order to achieve similar metallurgical effects, the braking strength should increase with the increase of casting speed and slab width. Using the strong EMBr field in a lower casting speed might reverse the desired effects. There exist some differences of solidified shell thinning features for different steel grades in the range of the funnel opening region under the measured operating conditions, which may affect the optimization of the casting process in a CSP caster.
39
Zhang, Pei, Feng Shan Du, Zhi Qiang Xu, and Ling Ling Zhao. "Numerical Simulation on the Dendritic Spacing and Microporosity in A356 Alloy Ingot." Materials Science Forum 575-578 (April 2008): 115–20. http://dx.doi.org/10.4028/www.scientific.net/msf.575-578.115.
Анотація:
A stochastic mathematic model contained the effects of dendrite morphology, solidification shrinkage and dissolved gases was formed to simulate microporosity formation and growth. Microporosities appear in the interspaces of primary dendrites as well as secondary dendrites from microscopic view of A356 aluminum alloy experimental ingot with a metal mold. In the past literatures it took the volumetric fraction of microporosities as a function of the local density. In the present work a single pore size and distribution were predicted concerning the combination of shrinkage and dissolved gases and dendritic spacing. The dendritic spacing is a main parameter to decide the pore pattern. For shrinkage and dissolved gases causes, the favorable one is determined by dendritic spacing, also the local cool rate and tip growth rate. The dense degree of the experimental ingots in different casting conditions was discussed. The variations of dens degree from the measured values in different casting conditions are similar to that of porosity volume fraction from the predicted results.
40
Olofsson, Jakob. "Integrated fatigue life predictions of aluminium castings using simulated local microstructure and defects." IOP Conference Series: Materials Science and Engineering 1281, no. 1 (May 1, 2023): 012067. http://dx.doi.org/10.1088/1757-899x/1281/1/012067.
Анотація:
Abstract In this work, an integrated simulation approach previously developed for static FE analyses is extended to microstructure- and defect-based fatigue life assessments of castings. The approach, the closed chain of simulations for cast components, combines casting process simulation with microstructure modelling and local material characterisation to generate heterogeneous material data for FE analysis and fatigue life assessment. The method is demonstrated on a High-Pressure Die Cast aluminium component. Areas with a high risk of defects are identified based on the simulated solidification conditions, and heterogeneous material data for the fatigue life analysis is generated. Fatigue testing has been performed with different levels of porosities to quantify the effect of defects on the element-specific Wöhler curves. Pore characteristics are assessed using 2D X-ray, fracture surface analysis and Kitagawa diagram. The results highlight the importance of taking the risk of defect formation into consideration when designing industrial aluminium castings subjected to fatigue loads.
41
Sharifi, Pouya, Kumar Sadayappan, and Jeffrey T. Wood. "The Effects of Interfacial Heat Transfer Coefficient on the Microstructure of High-Pressure Die-Cast Magnesium Alloy AM60B." Materials Science Forum 879 (November 2016): 1755–59. http://dx.doi.org/10.4028/www.scientific.net/msf.879.1755.
Анотація:
This paper describes the details of a quantitative experimental and numerical study on the influence of solidification conditions, including the apparent interfacial heat transfer coefficient (IHTC) between the die and solidifying metal, on the resulting local microstructure. Multiple runs of the commercial casting simulation package, ProCASTTM, are used to model the mold filling and solidification events employing a range of IHTC values. The simulation results are used to estimate the centreline cooling curve at various locations through the casting. The centreline cooling curve, together with the die temperature and the thermodynamic properties of the alloy are then used as inputs to compute the solution to the Stefan problem of a moving phase boundary, thereby providing the through-thickness cooling curves at each chosen location of the casting. Finally, the local cooling rate is used to calculate the resulting grain size and skin thickness via previously established relationships. A comparison of the predicted and experimentally determined grain size profiles enables the determination of the apparent IHTC, which, in this study, was approximately 12000 W/m2·K. Additional useful observations from the numerical study suggest that the IHTC has a significant influence on the skin thickness and grain size in both the skin and core regions of the casting, while the effect of die temperature is limited to influencing the skin grain size only.
42
Varoto, L., M. Chosson, J.-J. Blandin, A. Papillon, S. Roure, and G. Martin. "Microstructural evolutions induced by an electrical breakdown in a binary Cu-25Cr alloy." IOP Conference Series: Materials Science and Engineering 1249, no. 1 (July 1, 2022): 012023. http://dx.doi.org/10.1088/1757-899x/1249/1/012023.
Анотація:
Abstract Cu-Cr based alloys with a high Cr content are widely used as electrical contact materials in vacuum interrupters due to their good combination of electrical, thermal, and mechanical properties. During a current interruption process in a vacuum, the establishment of an electrical arc results in a severe local thermal input onto the contact material surface. Few studies have closely investigated the microstructural evolution during this phenomenon as well as the Cu-Cr alloy properties evolution. This study reports the microstructural, electrical conductivity, and hardness evolution of a Cu-25Cr (25 wt%Cr) solid state sintered alloy as electrical contact before and after successive current interruptions. Electron scanning and optical microscopy show that this microstructural evolution is a result of a complex phenomenon. Local and heterogeneous thermal conditions take place resulting in significant microstructural evolution. The resulting microstructure is related to out-of-equilibrium solidification conditions. Electrical conductivity is decreased by half in the whole thermally affected zone by the electrical arc and hardness is multiplied by three to four times.
43
Burbelko, Andriy A., Edward Fraś, Wojciech Kapturkiewicz, and Daniel Gurgul. "Modelling of Dendritic Growth during Unidirectional Solidification by the Method of Cellular Automata." Materials Science Forum 649 (May 2010): 217–22. http://dx.doi.org/10.4028/www.scientific.net/msf.649.217.
Анотація:
Modelling was carried out to investigate the internal dendrite grains structure formation from a liquid two-component solution in the area adjacent to a mould wall. For the simulation, our own model and computer program based on CAFD (Cellular Automata Finite Differences) were used. In modelling, the effect of process conditions and material-related parameters, e.g. nucleation temperature, heat exchange rate, interfacial energy, crystal orientation with respect to the casting wall, etc. on the nature of the dendritic grain growth was examined. It was demonstrated that the profile of concentration field in a near-mould-wall zone impedes the growth of the solid phase in the direct vicinity of the wall. A local melting down of the grains of a solid phase due to the segregation of admixtures reducing the alloy point of liquidus is also possible.
44
Sobolev, S. L. "Comparative study of solute trapping and Gibbs free energy changes at the phase interface during alloy solidification under local nonequilibrium conditions." Journal of Experimental and Theoretical Physics 124, no. 3 (March 2017): 459–68. http://dx.doi.org/10.1134/s1063776117020169.
45
Kim, Young Chan, Se Weon Choi, and Chang Seog Kang. "Effect of Controlling Process Parameters on Shrinkage Porosity in Aluminum Die-Casting Rotor." Advanced Materials Research 813 (September 2013): 136–43. http://dx.doi.org/10.4028/www.scientific.net/amr.813.136.
Анотація:
Aluminum rotor prone to have many casting defects especially large amount of gas and shrinkage porosity, which caused eccentricity, loss and noise during motor operation. Many attempts have been made to develop methods of shrinkage porosity control, but still there are some problems to solve. In this research, the process of vacuum squeeze die casting is proposed for limitation of defects. The 6 pin point gated dies which were in capable of local squeeze at the end ring were used. Influences of filling patterns on HPDC were evaluated and the important process control parameters were high injection speed, squeeze length, venting and process conditions. By using local squeeze and vacuum during filling and solidification, air and shrinkage porosity were significantly reduced and the feeding efficiency at the upper end ring was improved 10%. As a result of controlling the defects, the dynamometer test showed improved motor efficiency by more than 4%.
46
SCHULZE, T. P., and M. GRAE WORSTER. "Weak convection, liquid inclusions and the formation of chimneys in mushy layers." Journal of Fluid Mechanics 388 (June 10, 1999): 197–215. http://dx.doi.org/10.1017/s0022112099004589.
Анотація:
We present a numerical study of steady convection in a two-dimensional mushy layer during solidification of a binary mixture at a constant speed V. The mushy layer is modelled as a reactive porous medium whose permeability is a function of the local solid fraction. The flow in the liquid region above the mushy layer is modelled using the Stokes equations (i.e. the Prandtl number is taken to be infinite). The calculations follow the development of buoyancy-driven convection as the flow amplitude is increased to the level where the solid fraction is driven to zero at some point within the mushy region. We show that this event cannot occur before the local buoyancy-driven volume flux exceeds the solidification rate V. Further increases in the flow amplitude lead to the formation of a region with negative solid fraction, indicating the need to switch from the Darcy approximation to the Stokes flow approximation. These regions ultimately become what are known as chimneys. We exhibit solutions which give the detailed structure of the temperature, solute, flow and solid fraction fields within the mushy layer. A key finding of the numerics is that these fledgling chimneys emerge from the interior of the mushy layer, rather than eating their way down from the top of the layer, as the amplitude of the steady convection is increased. We discuss some qualitative features of the resulting liquid inclusions and, in the light of these, reassess the interfacial conditions between mushy and liquid regions.
47
Böttger, B., and M. Apel. "Phase-field simulation of the formation of new grains by fragmentation during melting of an ABD900 superalloy." IOP Conference Series: Materials Science and Engineering 1281, no. 1 (May 1, 2023): 012008. http://dx.doi.org/10.1088/1757-899x/1281/1/012008.
Анотація:
Abstract Laser powder bed fusion (L-PBF) is an additive manufacturing method which involves local laser melting of powder particles, a partial remelting of previously deposited layers, and subsequent re-solidification under high thermal gradients and cooling rates. The transition between melting and re-solidification becomes visible as melt pool boundaries in optical micrographs and plays a crucial role: Apart from creating a strong segregation zone, the transition determines whether the microstructure is inherited and carried over to the next layer, or whether new grains with new orientations are formed. While heterogeneous nucleation is suppressed due to the lack of seeding particles at the small length scales inherent to L-PBF, alternatively, new grains can form via dendrite fragmentation, as demonstrated in this paper by phase-field simulations using the software MICRESS®. By strong coupling between the phase-field equation and a thermal 1D-cylinder approach for the long-range temperature field, consistency between latent heat and microstructure is ensured. To allow for a systematic variation of the orientation relationship between the dendrite growth direction and the respective temperature gradient, a two-step simulation procedure for two overlapping tracks with variable gradient directions is developed. Growth conditions which promote fragmentation and formation of new grains are analyzed and discussed.
48
Kang, Jun-Yun, Jaecheol Yun, Byunghwan Kim, Jungho Choe, Sangsun Yang, Seong-Jun Park, Ji-Hun Yu, and Yong-Jin Kim. "Micro-Texture Analyses of a Cold-Work Tool Steel for Additive Manufacturing." Materials 13, no. 3 (February 9, 2020): 788. http://dx.doi.org/10.3390/ma13030788.
Анотація:
Small objects of an alloy tool steel were built by selective laser melting at different scan speeds, and their microstructures were analyzed using electron backscatter diffraction (EBSD). To present an explicit correlation with the local thermal cycles in the objects, prior austenite grains were reconstructed using the EBSD mapping data. Extensive growth of austenitic grains after solidification could be detected by the disagreement between the networks of carbides and austenite grain boundaries. A rapid laser scan at 2000 mm/s led to less growth, but retained a larger amount of austenite than a slow one at 50 mm/s. The rapid scan also exhibited definite evolution of Goss-type textures in austenite, which could be attributed to the growth of austenitic grains under a steep temperature gradient. The local variations in the microstructures and the textures enabled us to speculate the locally different thermal cycles determined by the different process conditions, that is, scan speeds.
49
Antonysamy, Alphons A., Philip B. Prangnell, and Jonathan Meyer. "Effect of Wall Thickness Transitions on Texture and Grain Structure in Additive Layer Manufacture (ALM) of Ti-6Al-4V." Materials Science Forum 706-709 (January 2012): 205–10. http://dx.doi.org/10.4028/www.scientific.net/msf.706-709.205.
Анотація:
In titanium alloys it is known that in bulk sections the solidification conditions in ALM commonly lead to undesirable, coarse, columnar β grain structures. Here, we have investigated the effect of build geometry on the grain structure and associated texture in Ti-6Al-4V ALM components produced by Selective Electron Beam Melting (SEBM). Through reconstruction of the primary β-phase, it has been confirmed that in thick sections large columnar β grains grow with a strong <001>βfibre texture, although there is a significant skin effect. In contrast, in thin walls nucleation off the surrounding powder and growth inwards dominates. Local heterogeneities are also observed within section transitions. It is shown that the weaker α transformation texture arises from a random distribution across the possible habit variants.
50
Dudorov, Maxim V., Alexander D. Drozin, and Victor P. Chernobrovin. "Thermodynamic Regularities of Nuclei Growth during Crystallization of Metastable Alloys." Solid State Phenomena 299 (January 2020): 436–41. http://dx.doi.org/10.4028/www.scientific.net/ssp.299.436.
Анотація:
The process of crystal growth in a metastable multicomponent melt has a high speed of the solidification front, which captures atoms of some other components. As a result of such a growth, at the surface of the growing crystal the effect of “impurity capture” is observed, and the concentrations of components significantly deviate from the local equilibrium. Under such conditions, the conventional physico-chemical methods for description of processes at the interfacial surface become inapplicable. Therefore, a new variational approach was applied for an integrated description of diffusion and thermal processes at the phase interface. The growth rate of crystal nucleus in a metastable melt was obtained, using the methods of non-equilibrium thermodynamics. The developed approach allows estimation of the degree of metastable effects influence on a crystal growth rate.