bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multiphase-field modelling of hydrogen pore evolution during alloy solidification
Authors: Zhang A , Guo Z , Wang Q , Xiong S 
Published: June 2020

Abstract
Gas porosity is recognized as one of the most common defects that can severely deteriorate the mechanical properties of solidified materials. Simulating the gas porosity in castings is challenging due to intricate multiphase interaction. In this work, a multiphase-field model is developed to simulate the evolution of both solid phase and hydrogen pore during solidification in the Al-Cu alloy. The driving forces for the solid-liquid and liquid-gas transitions are the undercooling and pressure difference respectively. Results show that the presence of hydrogen pore substantially changes the dendrite network. The Cu element accumulates near the solid-liquid interface due to solute partition. The pore causes a local hydrogen reservoir and Cu vacuum region, which elevates the average hydrogen content and retards the dendrite growth by blocking Cu diffusion.
Advanced modeling of shrinkage porosity in castings
Authors: Esser P , Schankies C , Khalajzadeh V , Beckermann C 
Published: June 2020

Abstract
Porosity due to solidification shrinkage is a troublesome defect in all types of metal castings. It limits the performance of cast components by adversely affecting the material’s strength, fatigue and creep properties. By reliably predicting porosity in casting process simulation, it can be minimized or eliminated. Here, a newly developed model for predicting porosity is presented. The model is based on the recent discovery that all shrinkage porosity nucleates and grows in regions of a casting where the solid fraction is the lowest. It calculates the feeding flows and pressure distribution in the liquid while accounting for the liquid density variation during cooling and solidification. It predicts the location, extent and amount of all types of shrinkage porosity in a casting, including riser pipes and large internal holes, surface sinks, and distributed micro-shrinkage. The model is numerically implemented in a standard casting simulation code. Comparisons to measurements in specially made steel castings demonstrate the capability of the model to accurately predict various types of shrinkage porosity.
A meshless solution of a of lid-driven cavity containing a heterogeneous porous medium
Authors: Hatić V , Rek Z , Mramor K , Mavrič B , Šarler B 
Published: June 2020

Abstract
The main objective of the present paper is to define and evaluate a benchmark test for solving the Navier-Stokes equations in heterogeneous porous medium. The benchmark is of high relevance for proper numerical simulation of flow pattern in the liquid-solid phase-change related phenomena. The test case represents a lid-driven square cavity which consists of a solid, a liquid, and a mushy part. Three different variations of the problem are solved, in which the ratio between the liquid and the mushy part is modified. The Reynolds and the Darcy number of this case are equal to 400 and 2.5×10−10, respectively. The Navier-Stokes equation, with an additional source term to take into account the Darcy effect, is solved with the local meshless diffuse approximate method. The method is structured by using the second-order polynomial basis vector and the Gaussian function to evaluate the weighted least squares approximation. The explicit Euler scheme is used to perform the time discretisation. The non-incremental pressure correction scheme is used to couple the pressure and velocity fields. Results are presented in terms of stream function, velocity magnitude, and mid-plane velocity profiles in the steady state. The accuracy of the numerical method is evaluated by a comparison with the finite volume solution obtained with a commercial solver and an investigation of the node arrangement effect.
Prediction of solidification structures in a 9.8 tonne steel ingot
Authors: Gerin B , Combeau H , Založnik M , Poitrault I , Cherif M 
Published: June 2020

Abstract
The control of the carbon macrosegregation level in steel ingots is important for the structural integrity of the final component. Previous studies using the SOLID® multiscale modelling software have shown that in order to obtain predictive results for the macrosegregation and the grain structure (CET, grain morphology) in steel ingots, a model needs to account for fragmentation of columnar dendrites as a source of equiaxed grains. The goal of this study is to show that a numerical model that takes into account fragmentation can describe the formation of the structures and the macrosegregation during solidification of a large steel ingot. The present article describes how fragmentation is taken into account in the multiphase numerical model used in the simulations. The simulation results are compared to experimental data from a 9.8 tonne ingot cast in A5/6 steel by ArcelorMittal Industeel. The model correctly reproduces the major features of the experimentally observed structure and macrosegregation. We show that the structures are formed very early on during solidification, whereas macrosegregation develops much more gradually. Our results also underline the importance of liquid flow and grain movement in order to correctly predict the final structure and macrosegregation.
Multiscale solidification simulation of Sr-modified Al-Si-Mg alloy in die casting
Authors: Zhou B , Laschet G , Eiken J , Behnken H , Apel M 
Published: June 2020

Abstract
Thermomechanical casting simulations incorporating solidification models are widely applied to improve the dimensional accuracy of casting components. The solidification path is commonly described based on Scheil-Gulliver assumptions which however fail to describe the effect of Strontium in Sr-modified Al-Si-Mg casting alloys. Strontium, even in small amounts, strongly affects the solidification morphology of the Al-Si eutectic together with its growth undercooling and hence the fraction solid–temperature relation during later stages of solidification. In order to address this problem, a dedicated micro-macro simulation approach is proposed here. The macroscopic thermomechanical casting simulation is linked with a spatially resolved multi-phase field simulation of the microstructure. Due to the fine fibrous morphology of the Si eutectic, a two-level homogenization scheme was applied to derive the effective mechanical properties of the Al alloy during its solidification. The proposed multiscale simulation and homogenization approach was applied to a permanent mould casting using an axisymmetric bowl cast from A356 for experimental validation.
A verification of thermophysical properties of a porous ceramic investment casting mould using commercial computational fluid dynamics software
Authors: Jones C A , Jolly M R , Jarfors A E W , Irwin M , Svenningsson R , Steggo J , Eriksson J 
Published: June 2020

Abstract
Defects in cast metals remain a common problem in many areas of the foundry industry, particularly in the investment casting of large area, thin-walled components for aerospace applications. During previous research, the thermophysical properties, density and porosity of a fibre reinforced ceramic investment casting mould were determined using several experimental techniques. Without verification, these experimental results remain nothing more than educated guesswork. The purpose of this study is to verify previous results and to more fully characterise the ceramic mould material with complementary measurements. A commercially available computational fluid dynamic (CFD) simulation package, Flow-3D®, was used in conjunction with a full-scale Ni-superalloy (IN718) casting to assess the accuracy of these results. By placing thermocouples strategically across the mould thickness, temperature profiles were determined and compared directly to predicted profiles extracted from the simulation by a custom-written Python script.
X-ray tomography, digital volume correlation and FE modelling: A synergistic combination to study the processing-structure-property relations in ductile iron
Authors: Andriollo T , Zhang Y , Fæster S , Thorborg J , Tiedje N S , Kouznetsova V , Hattel J 
Published: June 2020

Abstract
The mechanistic understanding of the processing-structure-property relations in ductile iron is still far from complete. One reason is that the impact on the mechanical properties of some of the microstructural features arising from the casting process can be hard or even impossible to investigate using experimental methods alone. The present work shows that a solution can be the synergistic combination of X-ray tomography, digital volume correlation (DVC) and finite element modelling, which are applied here to study the effect played by the Si micro-segregation and local residual stresses upon mechanical loading. First, miniaturized tensile and compact tension specimen are loaded incrementally while imaging with X-ray tomography. Then, the micro-scale displacement is reconstructed with DVC and used to prescribe the boundary conditions in high-fidelity 3D finite element models of the microstructure. Simulations are run considering or not the formation of the local residual stresses and build-up of micro-segregation during manufacturing. The numerical predictions are compared to the corresponding experimental data both at the macro-scale – applied load – and at the micro-scale – strain field reconstructed with DVC. This allows for a first assessment of the impact of the local residual stresses and Si micro-segregation on the mechanism of tensile deformation as well as of crack propagation of ductile iron.
Impact of local Si segregation on strain localization in ductile cast iron
Authors: Xu C L , Andriollo T , Lin F , Zhang Y B , Hattel J , Tiedje N 
Published: June 2020

Abstract
The distribution of Si content in tensile deformed ductile cast iron has been characterized using electron microscopy and correlated to the strain distribution determined based on 3D tomography data collected before and after tensile deformation and digital volume correlation analysis. The results show that the high plastic strain regions localize in bands consisting of large graphite nodules and deformed matrix with high Si content connecting the graphite nodules in the first-to-solidify regions. The bands are aligned about 45° with respect to the loading direction, which is close to the maximum shear direction.
Impact of crystal sedimentation and viscoplastic semi-solid dynamics on macrosegregation
Authors: Rodrigues C M G , Ludwig A , Wu M , Kharicha A , Vakhrushev A 
Published: June 2020

Abstract
A numerical investigation of melt convection with solid-phase transport during equiaxed solidification is performed to examine the structural and compositional evolution of an Al-Si alloy. Nucleation and growth kinetic laws are coupled with the general conservation equations employed in fluid dynamics to predict the development of the solidification structure. Besides crystal sedimentation due to buoyancy-induced forces in the low solid fraction range, the model covers also the viscoplastic semi-solid dynamics at high solid fractions. A test case is devised such that two viscoplastic structures grow from the vertical walls towards the centre of the domain and eventually merge at an arbitrary distance from the bottom of a simple cavity setup. This introduces difficulties for the solidification-driven feeding flow which has been associated with pressure drops across the domain. Dilatation of the mush is also predicted in the lower part of the solidifying viscoplastic mush, which means that additional melt is drawn to this area. Interestingly, besides liquid feeding, also a significant amount of solid feeding has been detected to compensate for solidification shrinkage. Such synergetic behaviour between the phases is analysed in terms of macrosegregation.
Sensitivity of macroscopic transport calculations to uncertain microscale relationships during metal alloy solidification
Authors: Coleman J , Krane M J M 
Published: June 2020

Abstract
The formation of grains during metallic solidification results in a multiphase system consisting of many moving interfaces. Models have been formulated in terms of variables describing the microscopic details of interface motion during solidification, but the computational cost prohibits their extension to the length scale of industrial castings. For this reason, macroscopic transport equations are mathematically formulated using averaging methods to replace the instantaneous description of interfaces. The most common approach is the volume-averaged, Eulerian approach relying on both the proper derivation of macroscopic field equations as well as uncertain interfacial conditions used to account for the average behavior of the interphase transfer occurring on the sub-grid length scale. In this work, common models used to describe the microsegregation occurring during solidification are evaluated in terms of the uncertainty of parametric inputs invoked in each model and their effect on macroscale predictions. We show that the qualitative macroscale predictions are not significantly changed by using more sophisticated microsegregation models, however significant uncertainty in input parameters used to describe the unresolved sub-grid interface is accumulated. Therefore, the use of simplified models is preferred until the uncertainty in model inputs can be reduced.
Microsegregation model including Soret effect: an application for Sn-Bi alloy
Authors: Santos Filho J E , Heringer R 
Published: June 2020

Abstract
We present an application of a microsegregation model that takes into account the Soret effect. This model, summarized here, lies in the context of the evaluation of thermodiffusion influence in alloys solidification. Initially, we deal with the thermodiffusion effect on the microsegregation scale. Subsequently, the Soret effect on macrosegregation shall be analyzed. The present model was conceived with similar considerations compared to the Gulliver-Scheil approach. A dimensionless parameter emerged from the model, which is potentially useful for assessing the Soret effect on the solidification of binary alloys. In the present work, this parameter was applied to an Sn-Bi alloy. The microsegregation model including the Soret effect can be widely used in the study of solute redistribution.
Cellular automaton modelling of M7C3 carbide growth during solidification of Fe-C-Cr alloy
Authors: Zhang H W , Zhang S , Wang Y C , Hao Y Z , Miao M , Nakajima K , Lei H , Wang Q , He J C 
Published: June 2020

Abstract
A microscopic cellular automaton combined with macroscopic heat and solute transport was developed to simulate the mutual growth and evolution of austenite and M7C3 carbide grains during Fe-C-Cr ternary alloy solidification process. The diffusion of solute C and Cr are contributed together to the constitutional undercooling, together with curvature undercooling, for obtaining the grain growth rate of austenite and M7C3 carbide. Results show that, the absorption of solute C and Cr by M7C3 grain and rejection by austenite grain promote the two grains’ cooperative growth. Once they approach to each other, the austenite grain quickly overgrows towards the M7C3 grain till finally envelops it. The simulated solidification morphology of the Fe-4wt%C-17wt%Cr alloy, predicted averaged grain size of M7C3 carbides and C and Cr concentration in austenite grains agree with the experimental measurements and solidification path prediction. The predicted average liquid concentration curve fits with the LR, GS and PE prediction at the initial M7C3 precipitation regime and after austenite grains fully enveloping towards the M7C3 grains, returns to overlap the LR, GS and PE prediction curves.
Three-dimensional needle network model for dendritic growth with fluid flow
Authors: Isensee T , Tourret D 
Published: June 2020

Abstract
We present a first implementation of the Dendritic Needle Network (DNN) model for dendritic crystal growth in three dimensions including convective transport in the melt. The numerical solving of the Navier-Stokes equations is performed with finite differences and is validated by comparison with a classical benchmark in fluid mechanics for unsteady flow. We compute the growth behavior of a single equiaxed crystal under a forced convective flow. As expected, the resulting dendrite morphology differs strongly from the case of the purely diffusive regime and from similar two-dimensional simulations. The resulting computationally efficient simulations open the way to studying mechanisms of microstructure selection in presence of fluid flow, using realistic alloy and process parameters.
3D cellular automaton modelling of silicon crystallization including grains in twin relationship
Authors: Pineau A , Guillemot G , Reinhart G , Regula G , Mangelinck-Noël N , Gandin Ch-A 
Published: June 2020

Abstract
Production of silicon for solar cells in photovoltaic systems is mainly based on directional casting processes. Twin nucleation is favoured during silicon growth due to the low-level twin energy of formation. As a consequence, in all solidification process, a large amount of grain boundaries (GB) are in twin relationship. A 3D cellular automaton (CA) model has been recently developed for the growth of multi-crystalline silicon including facet formation and nucleation of new grains in twin relationship. Activation of facets is based on an undercooling parameter assigned to each grain and for each of the <111> crystal directions. The model also considers nucleation and growth of grains on <111> facets corresponding to Σ3 twin relationships between twin grains. This model is first applied to comparison with experimental observations. It is found that impingement of growing grains that nucleated in Σ3 twin relationships meet during growth and form Σ3, Σ9 and Σ27 GB, in good agreement with experimental observations. Finally, the model is applied at a larger scale to generate grain structures representative of industrial practice. While quantitative experimental data is missing for comparison at such scale, the model is promising and its implementation in heat and mass transfer models should be considered for assistance to production of silicon for solar cells dedicated to photovoltaic systems.
Molecular dynamics simulation of heterogeneous nucleation from concave cavity at surface of grain refiner
Authors: Fujinaga T , Shibuta Y 
Published: June 2020

Abstract
Grain refiners are often used in practical production processes of metallic materials to promote and control nucleation. Although morphology of the grain refiner strongly affects nucleation behaviour, it is not well understood how unevenness of surface of the grain refiner affects nucleation from atomistic viewpoint. In this study, effect of concave cavity at surface of the grain refiner on heterogeneous nucleation is investigated by molecular dynamics (MD) simulation. HCP-Ti cube with a concave cavity is employed in the MD simulation as a grain refiner of the solidification of undercooled Al melt as a model study. HCP-Al solid is firstly formed at the tip or on the side wall of cavity and FCC-Al growth is followed on the exposed (0001) surface of HCP-Al for most of the cavities, whereas FCC-Al solid is directly formed on HCP(0001) terraces at the side wall of the cavity with large-obtuse apex angle.
The integration of structural mechanics into microstructure solidification modelling
Authors: Soar P , Kao A , Djambazov G , Shevchenko N , Eckert S , Pericleous K 
Published: June 2020

Abstract

In situ structural mechanics are an often neglected area when modelling alloy microstructure during solidification, despite the existence of practical examples and studies which seem to indicate that the interaction between thermal or mechanical stresses and microstructure can have a significant impact on its evolution and hence the final properties at a macroscopic level. A bespoke structural mechanics solver using the finite volume method has been developed to solve the linear elasticity equations, with design choices being made to facilitate the coupling of this solver to run in situ with an existing solidification model. The accuracy of the structural mechanics solver is verified against an analytic solution and initial results from a fully coupled system are presented which demonstrate in a fundamental example that the interaction between structural mechanics and a solidifying dendrite can lead to a significant change in growth behaviour.
Calphad-based phase-field study of the interplay between spheroidal graphite growth and chemical segregation in ductile cast iron
Authors: Eiken J 
Published: June 2020

Abstract
Spheroidal graphite in ductile cast irons forms in a divorced eutectic solidification, controlled by interstitial diffusion of carbon through the enveloping austenitic shell. As technical cast irons are multicomponent alloys, carbon diffusion can strongly be affected by content and chemical gradient of other solute elements. During growth of a eutectic cell, all solute elements are partitioned at the austenite/liquid interface. Substitutional diffusion within the austenite is almost negligible, but expansion-induced spatial displacement of the iron-rich matrix and solute atoms during graphite growth significantly complicates multidimensional numerical simulation. A recently developed volumetric multi-phase-field approach, implemented in the Micress software, now accounts for the volume expansion and related matter and solute transport. In the present case study, this approach is applied to investigate the evolving chemical gradients and their potential effect on carbon diffusion during growth of a three-dimensional eutectic cast iron cell. Phase and concentration dependent thermodynamic data, partial molar volumes and diffusion coefficients are evaluated from linked Calphad-databases. The interface properties of the polycrystalline spheroidal graphite nodule are modelled based on a dedicated effective multi-facetted anisotropy function. A special target is to investigate whether increase in Si content may result in a significant reduction of the carbon flux, eventually favoring graphite degeneration and chunky growth.
Effects of Bi addition on Si features, tensile properties and wear resistance of hypereutectic Al-15Si alloy
Authors: Pereira C L , Gomes L F , Spinelli J E 
Published: June 2020

Abstract
Al-Si alloys are very important in the automotive industry. This is thanks to their high strength to weight ratio, suitable fluidity, good corrosion resistance and high productivity. The shape of the eutectic Silicon (Si) has been widely studied since it is considered an index of quality regarding many application properties. Understanding the effects of alloy additions on the morphology of Si has drawn researcher’s attention. One of these elements of interest is Bismuth (Bi), which may be part of the composition of Al-Si alloys either as an addictive or a contamination. Hence, the microstructure aspects related to the presence of Bi are important requiring further consideration. In the present study, Al-15wt% Si hypereutectic alloy is modified with 1.0 wt% Bi. The goal is to compare the effect of this addition on the morphology of the phases forming the microstructure and on tensile/wear properties. In order to pursue that comparison, previously available data for the binary Al-15wt% Si alloy will be used. Various samples characterized by distinct cooling rates were generated by transient directional solidification of the ternary Al-Si-Bi alloy. The experimental variations of the eutectic spacing will be compared to each other based on their trends. It was found that the addition of minor Bi content (∼1%) permitted tensile strength and ductility of 195 MPa and 14%. Furthermore, wear resistance was improved thanks to Bi. The reasons for that will be outlined.