Progress Of Solidification Research Articles

Research progress of geopolymer solidification / stabilization of heavy metal contaminated soil

As a new type of green and environmentally friendly aluminosilicate gel material, geopolymer has attracted much attention from scholars for its good ability to immobilize heavy metals compared with traditional cement-based curing agents. Based on the research progress of geopolymer solidification of heavy metal contaminated soil at home and abroad in recent years, this paper introduces the process of geological polymerization reaction. The solidification mechanism of geopolymer on heavy metal contaminated soil and the influence of different factors on the solidification effect of geopolymer on heavy metal contaminated soil are described in detail. The leaching characteristics of heavy metals in geopolymer solidified heavy metal contaminated soil under freeze-thaw cycle, dry-wet cycle and carbonization were further discussed. Finally, the problems existing in the solidification of heavy metal contaminated soil by geopolymer are analyzed and the future research and development direction is prospected.

Performance assessment of multi-tube inline and staggered array based latent heat storage system

In this article, the charging and discharging characteristics of a shell and multi-tube latent heat storage system are investigated numerically to select a suitable array type for the multiple heat transfer tubes. This study considers nine tubes in eight different arrangements. Numerical simulations on simplified two-dimensional paraffin wax domain were performed using ANSYS Fluent. The results are depicted as contours and streamlines to visualize the progress of melting and solidification. The transient performance is evaluated based on the variation of liquid fraction, heat transfer rate at tube surfaces, melting time, and amount of energy stored with time. The results show that the rate of melting and energy storage performance depend greatly on the configuration of tubes. The staggered array with high tube pitch to tube diameter ratio (PR) cases reported better performance. By changing the arrangement of tubes, a 74.2 % reduction in melting time is observed for the staggered array with PR = 3.5, i.e. S3.5 case, as compared to the inline array with PR = 2, i.e. I2 case. By changing the arrangement of tubes, a 9 % improvement in the amount of energy stored is achieved for the S3.5 array compared to the I2 array for 300 min of charging. Unlike melting, solidification is governed by conduction thus for the same value of PR, the solidification time was almost the same for the both inline and staggered arrays. Higher PR cases performed faster solidification, and about 56 % reduction in solidification time is observed for PR = 3.5 as compared to PR = 2 cases.

A model volcanic fissure with adjustable geometry and wall temperature

Fissure eruptions initiate with magma ascending and spreading through cracks in the ground that can extend for kilometres at the surface. Eruptions eventually localise to form one or a few persistent conduits and ultimately an array of discrete cones or craters. We built a new experimental apparatus to investigate the influences of fissure shape and wall-rock temperature on localisation within a volcanic fissure, and the thermal feedbacks associated with variability of these parameters. Our artificial fissure, or “Artfish,” has a slot geometry with adjustable shape and wall temperature. We can simulate both starting variability in fissure geometry and wall temperature, as well as changes in these parameters during an experiment to replicate, for example, blockage by wall-rock collapse, widening by wall-rock erosion, and warming by adjacent intrusions. We use polyethylene glycol (PEG 600) for our analogue fluid. A variable-speed pump allows for a range of fluid injection and ascent rates. Initial tests showcase the capabilities of the model and the types of data that may be acquired. Additional key features achieved include a stable and planar injection system, fluid recycling, and the use of particle tracers for monitoring flow patterns and velocities. The thermal evolution of the fluid-wall interface is quantitatively measured with thermal sensors, and the change in state of the PEG provides a clear visual indication of flow behaviour and solidification progress recorded on video. The potential experiments that can be conducted with this highly versatile model are numerous and will be used to gain a better understanding of the thermal controls on flow localisation and conduit development. This will assist hazard modellers to assess controls on eruption evolution and potentially to forecast sites where an initial fissure eruption may focus.

Effect of casting temperature on the solidification process and (micro)structure of Zr-based metallic glasses

Bulk metallic glasses (BMGs) bear versatile advantages compared to traditional crystalline metallic materials. However, preparation of large size BMG components remains a great challenge due to the lack of understanding the casting dynamics of BMGs. The present work investigates the dynamics of the solidification process during casting of a Zr41.2Ti13.8Cu12.5Ni10Be22.5 BMG by measuring the time-dependent temperature evolution and constructing distance–time curves showing the progress of solidification. The experimentally probed temperature evolution proves that a higher casting temperature causes a lower cooling rate and induces more pronounced nanocrystal phase formation in the final BMG casting. Thus, optimization of the casting temperature is crucial for casting BMG components. The solidification coefficient K of the studied Zr-based BMG in copper mold was determined. The solidification time can be calculated with model: τ=M2K2. The solidification of the Zr-based BMG occurs in a narrow transition layer region following a “layer-by-layer” solidification mode. This feature is vital for designing the casting process appropriately to avoid the formation of casting defects in BMG components. The present work sheds new light on the solidification mechanism of bulk glass-forming liquids and underlines the importance of optimizing the technology and processing conditions for fabrication of BMG components with practical applications.

The performance of hydrogen desorption from a metal hydride with heat supply by a phase change material incorporated in porous media (metal foam): Heat and mass transfer assessment

Although heat management during hydrogen adsorption/desorption in metal hydride (MH) reactor using phase change material (PCMs)-based energy storage system has been researched in the last years, very limited data on large-scale applications is found. In this work, a 2D transient numerical model has been developed on Fluent 15.0 CFD platform to assess the performance of hydrogen desorption with consuming heat reduction in a large-scale metal-hydride (MH) storage reactor packed with LaNi5 and 4 MF-PCM (i.e. Metal Foam-Phase Change Material) tubes distributed in the MH-bed. The model was firstly validated by comparing the simulation outcomes with experimental data from other works. Mass and heat transfer resulted in the different parts of the cylindrical MH-MF-PCM reactor were analyzed; where the temporal temperature and energy profiles (average and contours), the MH-dehydrogenation kinetics, and the PCM solidification rate were established for different MFs (i.e. aluminum, copper, nickel and titanium) of varying porosities (10 to 100%). Outstanding results were found. The MF-PCM unit enhanced the MH performance (dehydrogenation) by discharging its latent heat to the MH-bed. The MH was completely discharged within ~700 s. Metal foams accelerated the PCM-solidification rate and the heat releasing to the MH, mainly when lower MF porosities are adopted (i.e. increasing the thermal conductivity of the PCM). The lower the MF porosity (the higher the conductivity), the higher is the energy lost during the sonification process. The PCM solidified rapidly with copper and aluminium MFs instead of nickel and titanium (thermal conductivity effect), with strong dependence on the tubes' position in the reactor bed. The PCM-tube above the H2-charging/discharging pipe solidifies more quickly than the other tubes, presumably to the gravitational effect. In conclusion, the solidification progress of the PCM in the different MF systems was markedly improved in the presence of lower porous MF of higher conductivity (Al and Cu), where the tube position plays a crucial role.

In Situ Investigation of the Solidification of Al-20 wt.% Zn Alloys Inoculated by Al-5Ti-1B

In situ synchrotron x-ray radiography studies on the solidification sequences of non-refined and refined Al-20Zn alloys were carried out. The dendrite growth, porosity evolution, grain densities and growth rates were measured. Without and with 0.05% grain refiner, the solidification sequences appear as columnar dendrite. The average columnar dendrite growth rate of non-refined Al-20Zn alloy is larger than refined by 0.05% grain refiner. The burst growth is happened in columnar dendrite which is the first report and the time interval was about 1.2s. The columnar interdendritic region is prone to form porosities with solidification progress. The equivalent diameter of porosity with time is well fitted by Gaussian function, and the growth velocities of porosities of all sequences are faster in the first seven seconds and fluctuated with time. When the addition level of grain refiner is larger than 0.1%, the solidification sequences appear as equiaxed dendrite. The accumulation of grains of refined Al-20Zn alloys is well fitted by logistic function. The porosities disappeared during solidification with equiaxed grains. The equiaxed dendritic growth velocity, which is ~16μm/s at a cooling rate of 8K/min, is much lower than columnar.

An analysis of the melt flow permeability for evolving hypoeutectic Al-Si mushy zone microstructures by phase field simulations

The evolution of 3D microstructures during solidification has been simulated by the phase field method for a hypoeutectic Al-Si-Mg casting alloy at the scale of a representative volume element (RVE) for isotropic and anisotropic thermal conditions. The corresponding evolution of the melt flow permeability is derived by solving the Navier-Stokes equation on this RVE, i.e. determining the flow for an applied pressure gradient. To characterize the microstructures their interfacial area density and their tortuosity were calculated. The solid fraction was used to track the progress of solidification. The predicted permeabilities of the microstructures can be fitted to a Carman-Kozeny equation amended by a parameter that accounts for the closure of open flow channels, i.e. the complete encapsulation of residual melt. Good agreement was found except for the solidification morphology resulting from anisotropic conditions. In this case, the permeability for the flow in the direction of the thermal gradient deviated at higher solid fractions. The reasons for this deviation are investigated and discussed. Overall, we demonstrate that effective melt flow permeabilities can be derived from microstructure simulations. It leads to a parameterized Carman-Kozeny relationship for the evolving permeability during solidification calibrated by microstructure simulations. This relation can be used in macroscopic casting simulations.

Effect of Ti Powders Addition on Mechanical and Metallurgical Properties of IN718/BNi-2/316L Diffusion Couple

Transient liquid bonding (TLP) of IN718 superalloy to 316L alloy was carried out using BNi-2 interlayer with Ti powders. Effect of Ti powders addition with 2 and 4 wt% Ti on metallurgical, diffusion and mechanical properties of joints bonded at 1050 °C for three bonding time 45 min, 2 h and 16 h was investigated. The microstructure of the diffusion zone was investigated by scanning electron microscopy, and the phases in the diffusion zone were analyzed by energy-dispersive spectroscopy. The shear strength and microhardness tests were carried out to investigate the mechanical properties of the joints. The results showed that the presence of eutectic and dendritic solidification increased by Ti addition. In addition to this, a continuous Ti-rich intermetallic layer was formed at the bonding region/316L interface. It was observed that TiB2 component was formed in the TLP joint and it led to reduced Nb boride in bonding region. The formation mechanism and solidification progress path of the IN718/BNi-2 + Ti powder/316L joint were proposed. The hardness in the joint containing Ti powders increased, but it had little effect on shear strength at room temperature.

Segregation behavior of Fe and Gd in molten corium during solidification progress

For a criticality assessment of the fuel debris generated by the Fukushima–Daiichi Nuclear Power Plant accident, knowing the segregation of neutron absorber materials, i.e., Gd, B, and Fe, in the fuel debris is necessary. Although B may mostly evaporate during melting, Fe and Gd are expected to remain in the molten corium. To understand the redistribution behavior of Gd and Fe during the solidification of the molten corium, solidification experiments with simulated corium (containing UO2, ZrO2, FeO, and Gd2O3 with a small amount of simulated fission products such as MoO3, Nd2O3, SrO, and RuO2) were performed using a cold crucible induction heating method. The simulated corium was slowly cooled from 2500 °C and solidified from the bottom to the top of the melt. An elemental analysis of the solidified material showed that the Fe-concentration in the inner region increased up to approximately 3.4 times that in the bottom region. This suggested that FeO might be concentrated in the residual melt and that, consequently, the concentration of Fe increased in the later solidification region. On the contrary, the Gd concentration in the periphery region was found to be approximately 2.0 times higher than that in the inner region, suggesting the segregation of Gd in the early solidified phase and to remain with the residual, UO2-rich phase even after oxidative losses. No significant segregation was observed for the simulated fission products.

Effects of solidification thermal parameters and Bi doping on silicon size, morphology and mechanical properties of Al-15wt.% Si-3.2wt.% Bi and Al-18wt.% Si-3.2wt.% Bi alloys

The use of bismuth (Bi) in aluminum (Al) industries is recognized as prime importance because of possible recycling as alloying element in special applications such as those enhancing machinability. The effects of Bi interaction on solidification progress as well as on the resulting microstructure of hypereutectic Al-Si alloys, i.e. the morphology and size of Si crystals are rare information. As such, the present research work investigates the characteristic parameters of eutectic and primary Si with addition of Bi for both ternary Al-15 wt.%Si- 3.2 wt.%Bi and Al-18 wt.%Si- 3.2 wt.%Bi alloys samples directionally solidified (DS) under various cooling rates. The alloy containing 15 wt.%Si showed that Bi acts in the suppression of the growth of primary Si crystals for samples solidified at cooling rates ranging from 2.0 to 31 K/s. For lower rates, a minor fraction of five-fold branched Si was recognized in transverse specimens. A mixture of globular-fibrous eutectic Si is shown to occur for eutectic cooling rates higher than 5 K/s. The Al-18 wt.%Si- 3.2 wt.%Bi alloy is characterized by a mixed structure of eutectic flaky Si and primary angular Si with intersecting spines at nearly 90º all over the entire range of experimental cooling rates (i.e., from 0.4 to 40 K/s). Despite the intricacy of the formed microstructures, it was possible to establish relationships between tensile properties and eutectic Si spacing in order to compare the properties between the tested alloys. Tensile strength and elongation decrease with increasing alloy Si content.

Microstructure and mechanical properties of directionally solidified Al2O3/YAG binary eutectic ceramic prepared with induction heating zone melting

In order to reveal the dependence of the microstructure and mechanical properties of directionally solidified eutectic ceramic (DSEC) on the growth rate so as to further improve its performance, Al2O3/Y3Al5O12 (YAG) DSEC with diameter Φ10.16 was prepared via induction heating zone melting (IHZM) method, and the effects of the growth rate on the phases’ distribution, eutectic spacing, hardness and fracture toughness of the DSEC were investigated. XRD patterns show that the crystallinity of the eutectic ceramic significantly improved after directional solidification. The DSEC displays a typical irregular eutectic microstructure like mosaic, YAG phase formed the matrix in which Al2O3 phase embedded. The eutectic constant is calculated λv1/2 = 8.944, the microstructure evolution during solidification progress is shown via nucleating and growth mode. The hardness and fracture toughness of the DSEC are 1.89 times and 1.42 times those of the sintered ceramic, respectively. The relationship between the hardness, fracture toughness and the growth rate are expressed as Hv=13.4+7.72v1/4 and KIC=2.24+2.48v1/4 via Hall-Petch equation.

Sn-Bi(-Ga) TIM Alloys: Microstructure, Tensile Properties, Wettability and Interfacial Reactions

In the present study, the main purpose is to examine the quality of the interface formed between either binary Sn-Bi or ternary Sn-Bi-2wt.%Ga Thermal Interface Material—TIM alloys and a copper (Cu) substrate. The characteristics of the formed intermetallic compound (IMC) films were analyzed in the as-soldered joints, as well as during isothermal heat treatments at 100°C for long periods of time. Thermo-Calc computations were also used in return for a better comprehension of the mechanisms involved, including, for instance, those related to the presence of Ga within the interdendritic regions. This can be explained by the increase in the Ga-amount in the liquid-phase with the progress of solidification. In an effort to address the wettability issue, the contact angles between the molten alloy and the Cu substrate were also determined. Finally, tensile tests were performed in order to evaluate the effects of the minor Ga additions in the alloy’s overall mechanical properties. Despite unsound alloy mechanical properties, gallium (Ga) additions effectively suppress the formation of the CuSn intermetallic by replacing it with a Cu9Ga4 IMC layer in the as-soldered material, which grew with less deleterious morphology and finer thicknesses.

Recent progress of solidification of suspensions

Suspensions include solvent and uniformly dispersed particles. Solidification of suspensions is to freeze the solvent while numerous particles disturb the pattern formation during the growth of the solid/liquid interface. It is a new interdisciplinary subject, involving the fields of freeze-casting porous materials, frost heaving, sea ice and biological tissue engineering and so on. Especially in recent years, many advanced materials with excellent properties were developed based on the processing of suspension solidification. Experimental phenomenon in suspension solidification is different from that in alloy solidification, such as the close-packed particle layer and self assembly, the ice lamellae structure and the periodic ice lenses and so on. Up to now, the formation mechanisms of these microstructures are still unclear. In this paper, we first review the historical development of suspension solidification in theory and in experiment. Then we demonstrate some recent progress of microstructural evolution and dynamical particle packing of suspension solidification. Finally, the outlooks of the future study on solidification of suspensions are also presented.

Grain Optimization: Optimizing Grain Selection Design in the Single-Crystal Solidification of Ni-Based Superalloys (Crystal Research and Technology 12/2018)

Crystal Research and TechnologyVolume 53, Issue 12 1870022 Cover PictureFree Access Grain Optimization: Optimizing Grain Selection Design in the Single-Crystal Solidification of Ni-Based Superalloys (Crystal Research and Technology 12/2018) First published: 13 December 2018 https://doi.org/10.1002/crat.201870022AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract This figure represents selection phenomenon of single crystal during directional solidification. The process begins by arbitrarily nucleation of equiaxed grains at the copper chill contact area. Further progress of solidification brings about a columnar structure which is accompanied by competitive grain growth. A single grain finally encompass the upper part after solidification of spiral grain selector has come to an end. More details can be found in article number 1800108 by Fazlollah Sadeghi, Ahmad Kermanpur, and Ebrahim Norouzi. Volume53, Issue12December 20181870022 RelatedInformation

Margin evaluation of in-vessel melt retention for small IPWR

In this paper, the safety margin of IVR (in-vessel melt retention) for small IPWR IP200 (integrated pressurized water reactor) is evaluated by numerical simulation. The thermal hydraulics and core degradation are modeled by SCDAP/RELAP5 code to provide initial conditions for the IVR. Meanwhile, the lower head behaviors are modeled by the finite element code COUPLE to present the dynamic evolution of molten pool with detailed temperature distribution. The transient analyses of thermal load firstly focus on the progression of corium solidification and external cooling, and then analogize to the IVR studies of other IPWRs to discuss the impacts which caused by the inherent design features of IP200. Besides, the differences between FIBS steady model and SCDAP transient model are discussed in terms of the heat transfer governing equation to summarize the benefits of transient calculation. In order to explain the calculation rationality, the result of maximum surface heat flux is also validated with the dimensionless data of related experiment. Finally, the mass composition of molten pool and the gap thermal resistance of inner wall are selected for parametric sensitivity analyses to assess the conservatism of maximum heat flux. For the quantitative conclusions, the low coolant storage of IP200 makes the core degradation very fast. The duration is about 9500s and the maximum temperature of liquid corium is close to 2900 K. The initial inner heat of molten pool is very high that the transient heat flux can get approximately 195% above the steady value. At the moment of maximum thermal load, the peak heat flux reaches 0.46 MW/m2, still lower than the local CHF. The lowest safety margin locates at the bottom angle and corresponding q/CHF is 0.65. The present work can provide references for the safety design of small IPWR.

Microstructural Evolution and Mechanical Properties Evaluation of IN-939 Bonds Made by Isothermal Solidification of a Liquated Ni-Cr-B Interlayer

The IN-939 superalloy was bonded under a high vacuum condition by isothermal solidification of a liquated Ni-Cr-B amorphous foil with a 38 μm thickness as the interlayer. The progression of isothermal solidification was completed at 1120 °C in the bonding time of 45 minutes and a single-phase gamma solid solution was formed at the centerline. Insufficient bonding times led to a formation of centerline eutectic products composed of gamma solid solution, Ni-rich boride, and Cr-rich boride phases. A reverse relationship between the bonding time and the width of eutectic micro-constituents was perceived. Some precipitates with blocky and widmanstatten morphologies were observed in the diffusion-affected zone (DAZ) which seemed to be Cr-rich borides. The maximum precipitation depth, the number, and the area fraction of DAZ precipitates were investigated. It was revealed that the microhardness distribution across the joints was governed by changes in the area fraction of DAZ precipitates. The applied shear tests demonstrated an increment in shear properties of the bonds by increasing the bonding time. A remarkable joint efficiency of ~ 83 pct accompanied by a high failure energy (~ 35 J) and displacement (~ 1.8 mm) was achieved in the bond made at 1120 °C for 60 minutes. The fractographic examination of the fracture surfaces illustrated two different dimple-like and semi-cleavage morphologies for the bonds with complete isothermal solidification and partial isothermal solidification, respectively.

Modeling of Crucial Process Parameters for the Continuous Improvement of Special Steels at the Stomana Plant

In this study, a heat transfer model that takes under consideration the micro-segregation phenomena and has been extensively deployed for solidification studies concerning the plant casters is also applied to show the casting speed and superheat effects upon internal soundness. Τhe solidification path of C45R, 42CrMo4, S355 grades was simulated using Thermocalc® and DICTRA software in order to examine the phases formed in crucial process temperature windows for the casting. Coupled Heat Transfer/Simple Micro-Segregation Model software has been deployed to simulate the effect of cooling rate on solidus temperature, and solid fraction during solidification. The solidus temperature results computed by the HT/SM and DICTRA were found to be in good agreement. However, the differences in the predicted solidification fractions may derive from the fact that DICTRA uses an average cooling rate whereas the heat transfer SM model takes into account also the local cooling rates in the solidification progress.

Transient liquid phase bonding of AZ31 magnesium alloy: Metallurgical structure and mechanical properties

In the present paper, AZ31 magnesium alloy was transient liquid phase bonded using aluminum interlayers (with two different thicknesses of 9 and 14 μm), two bonding temperature of 440 ̊ and 455 ̊C and different holding times. Optical and scanning electron microscopies were employed to determine the progression of isothermal solidification. In addition, X-ray diffraction method was used to determine the formation of the brittle Al12Mg17 compound. The hardness was found to be higher at the joint center compared to the joint sides, which can be related to the eutectic structure and high amount of intermetallic compounds at the center. The results showed that the 9 μm-interlayer led to greater shear strength, elongation and failure energy than the 14 μm interlayer, and the highest shear strength of ∼35 MPa was obtained for 75 min bonding time and 9 μm interlayer. The fracture surface evaluation revealed the presence of more plastic deformation for the joints made by the thinner interlayer.

Thermoelectric magnetohydrodynamic effects on the crystal growth rate of undercooled Ni dendrites.

In the undercooled solidification of pure metals, the dendrite tip velocity has been shown experimentally to have a strong dependence on the intensity of an external magnetic field, exhibiting several maxima and minima. In the experiments conducted in China, the undercooled solidification dynamics of pure Ni was studied using the glass fluxing method. Visual recordings of the progress of solidification are compared at different static fields up to 6 T. The introduction of microscopic convective transport through thermoelectric magnetohydrodynamics is a promising explanation for the observed changes of tip velocities. To address this problem, a purpose-built numerical code was used to solve the coupled equations representing the magnetohydrodynamic, thermal and solidification mechanisms. The underlying phenomena can be attributed to two competing flow fields, which were generated by orthogonal components of the magnetic field, parallel and transverse to the direction of growth. Their effects are either intensified or damped out with increasing magnetic field intensity, leading to the observed behaviour of the tip velocity. The results obtained reflect well the experimental findings.This article is part of the theme issue ‘From atomistic interfaces to dendritic patterns’.

A Literature Survey Of Methods To Study And Analyze The Gating System Design For Its Effect On Casting Quality

For the optimum design of gating system, the study of filling process is of great significance since it directly affects casting quality. The goal of proper mould filing cannot be achieved without proper gating design which influences the flow pattern, further affects the temperature distribution and modifies the progression of solidification. But it is not only expensive but difficult to observe the molten metal flow in the mould directly due to the opacity of sand mould.For the study and analysis of flow of molten metal through the gating system and into the mould cavity, many researchers have tried various techniques which can be broadly classified as direct observation method and through modelling the process by water analogy or by computational modelling.To get accurate and dependable prediction of the subtle transient events, one has to make a judicious combination of both methods for casting with an alloy system. Many researchers attempted to use numerical simulation techniques to analyse the molten flow through the gating system, which has an advantage to accurately predict subtle transient events and gain more profound information about the behaviour of metal stream. Considerable materials are available in literature to understand the influence of gating system design on mould filling using various techniques of direct observation validating the given design of gating system by using real time X-ray radiography to observe the flow of molten metal in a sand mould, or by using contact wire sensing method along with computerized data acquisition, or by using water analogy method to observe the flow of water in a transparent mould.Also few researchers attempted optimization of gating system in casting to control defects and maximize the effective yield of the cast products. This paper comprehensively review the available literature for various techniques to study, analyse and predict the flow behaviour of the melt in order to minimize the related defects arising due to melt flow and also increasing the effective yield of the casting with minimum effect on its quality.