Control Of Solidification Process Research Articles

Multifunctional architected MWCNTs/PDMS composites with high sensing and energy absorption capability inspired by ant tentacle and pomelo peel

The multifunctional features of pressure sensitivity and energy-absorption capability of flexible electromechanical sensors are desirable for practical applications, such as personal protection, crash mitigation, and protective packaging of sensitive elements. However, there are still challenges in developing ultrasensitive pressure sensors with high energy absorption capability. Herein, a bio-inspired flexible piezoresistive MWCNTs/PDMS composite with a multilayered architecture mimicking the ant tentacle and the pomelo peel is innovatively constructed, which can simultaneously detect physical stimuli in an extensive pressure range and absorb impact energy. The composite architecture is composed of the bottom-layer interlocked tentacle-like conical micropillars and the top-layer pomelo peel-inspired hierarchically enclosed-porous microstructure, which has successfully wrapped air inside to form a solid-gas dual phase structure with enhanced energy absorbing capability and piezoresistivity. The composite architecture was manufactured by a laser-engraving method associated with the controlled solidification process of the composite by regulating the vacuum pumping rate in the pre-curing condition. Owing to the hollow-shaped tentacle-like conical micropillars, the contact area can be dramatically increased within a subtle pressure loading, leading to superb pressure sensitivity of ∼26.1 kPa−1. Simultaneously, the hierarchically enclosed-porous structure with trapped air (gas-phase), acting as an air cushion packaging, imitating the pomelo peel provides the composite architecture with exceptional mechanical energy absorption of ∼2.74 MJ/m3 and an extensive pressure sensing range from 0.1 Pa to 60 kPa. As a result, the as-proposed composite sensor was able to detect mechanical signals such human finger tapping, wrist flexion, and pendulum hammer impact. Numerical simulations also showed that the wrapped air inside the hierarchical enclosed-porous structure improved the mechanical damping properties of the composite architecture. It is envisioned that our finding could contribute to the development of multifunctional materials to meet the growing demands for next-generation electronic systems, inspired by sophisticated architectures from nature.

Effect of Grain Refining on the Shrinkage Porosity in Thin-Walled Plates Produced by Investment Casting Integrating Controlled Solidification Technique

The production of high integrity thin-walled investment cast components can be achieved by controlling the solidification process. The aim of this work was to study the effect of grain refiner on thin-walled aluminum alloy A356.0 plates produced by investment casting using a controlled solidification process. Moulds with plate thicknesses of 0.7 mm, 1.5 mm and 2 mm were cast. The A356.0 alloy was melted in an electric resistance furnace, one mould was cast with controlled solidification process, second mould was cast using A356.0 modified with Strontium (Sr) (0.03%), grain refiner Aluminium Titanium Boron (Al-5Ti-B) (0.11%) and controlled solidification process. Melt temperature was stabilized at 700°C before being poured into the mould at 740°C. Moulds were inserted into a cooling medium at a controlled rate until the plates were submerged and held submerged for few minutes before being withdrawn. The microstructure and shrinkage porosity were assessed using optical microscope and the density was measured using the Archimedes principle. Qualitative assessment of the shrinkage porosity was measured using Image J software. Grain refinement was shown to reduce the size of primary dendrites. Shrinkage porosity decreased in samples. This was supported by the higher density observed for the grain refined casting.

Numerical investigation of grain refinement of magnesium alloys: Effects of cooling rate

Solidification experiment of Mg-4Y-3Nd-1.2Al (wt%) alloy cast in a step-like sand-mold casting shows that a slow cooling rather than a fast cooling leads to grain refinement during solidification with in-situ formed nucleant particles (Al2RE) in molten melt. A two-dimensional cellular automaton (CA) model is adopted to fundamentally understand the mechanism of grain refinement. Conservation equation of energy is solved at macro-scale. The generated thermal history serves as input for the CA simulation. The model predictions are verified against the experiment. A high cooling rate leads to fast dendrite growth and solute enrichment in the interdendritic region. The nucleant particles, in-situ formed under the fast cooling condition, have small sizes. A larger number of small-sized particles are suppressed because they do not experience enough constitutional undercooling to nucleate. A critical particle size exists, above which the grain refinement becomes less sensitive to the cooling rate measured in the experiment. The simulation of one particle transported to the interdendritic area shows it is more difficult for this particle to develop under the faster cooling condition. We expect this fundamental understanding of the physics of cooling rate for the grain refinement would have implications on future complex magnesium alloy designs as well as solidification process control.

Effect of Ta and Ti on the solidification characteristics of novel γ′-strengthened Co-base superalloys

The effects of Ta and Ti on the microstructure, segregation and solidification path of Co-7Al-8W-base alloy were investigated using directional solidification quenching experiments and isothermal solidification quenching experiments. The results showed that the as-cast microstructure of the Co-7Al-8W alloy (Base alloy) is the γ single phase. The Al element slightly segregates to the interdendritic regions, the W element slightly segregates to the dendritic core, and Co has almost no segregation. The solidification path of the Co-7Al-8W alloy is L→L1+γ→γ. With the addition of 1 at.% Ta, there is no change in the segregation of elements, the microstructure and the solidification path of the alloy. The Ta element strongly segregates to the interdendritic regions in the Co-7Al-8W-1Ta alloy. With the addition of 4 at.% Ti, the Ti element strongly segregates to the interdendritic regions, and the segregation of Al and W elements increases. Blocky γ′ phase and (β+γ′)e eutectics form in the interdendritic regions. The solidification path of the Co-7Al-8W-4Ti alloy is L→L1+γ→L2+γ+(β+γ′)e→L3+γ+(β+γ′)e+γ'→γ+(β+γ′)e+γ'. After the addition of 1 at.% Ta+4 at.% Ti, the segregation of Al, Ta and Ti decreases, while the segregation of W increases. Laves phase, blocky γ′ phase and (β+γ′)e eutectics form in the interdendritic regions. The solidification path of the Co-7Al-8W-1Ta-4Ti alloy is L→L1+γ→L2+γ+Laves→L3+γ+Laves+(β+γ′)e→L4+γ+Laves+(β+γ′)e+γ'→γ+Laves+(β+γ′)e+γ'. The above results could provide an experimental basis for composition optimization and solidification process control of novel γ′-strengthened Co-base superalloys.

Understanding non-parabolic solidification kinetics in Ni-based alloys during TLP bonding via thermo-kinetic modelling

Through a diffusion controlled solidification process, transient liquid phase (TLP) bonding is widely exploited to repair or join materials in different industry areas for decades. However, a lack of modeling on the TLP process of multi-component systems makes design of the TLP process an expensive trial and error process. Here, by coupling with experiment, we developed a set of self-consistent kinetic model parameters, which are used to simulate the TLP process of AWS A5.8 BNi-9 (filler)/Inconel 718 (base metal) at 1090 °C such as the solidification kinetics, diffusion profile and the precipitated borides in the Diffusion Affected Zone (DAZ). Consistent with experiment results by X-ray diffraction (XRD) and scanning electron microscopy (SEM), our simulation demonstrate four types of boride precipitated in the DAZ: MB2, MB, M5B3 and M3B2, which consequently results in the non-parabolic solidification behaviors in the brazing system. Based on the calculations using the developed models, we predict that a post heat treatment at 1090 °C for 3500s will homogenize the boride phase distribution in the DAZ, thus increasing the strength of the brazing joint. The developed model parameters may be extended to the other Ni-based alloys.

Solutioning and solidification process control in Ta-modified CM247 LC superalloy

Various stepwise solutionizing treatments were designed and performed to reach the highest secondary γ′ volume fraction and prevent incipient melting in a high Ta content Ni-base superalloy designed based on CM247 LC superalloy. Based on DSC thermal analysis data four different solutionizing cycles were selected and tried to eliminate the γ/γ′ eutectics and dissolve the primary γ′. Increasing Ta content from 3.2 to 6wt% in CM247 LC superalloy, raised the size and volume fraction of γ/γ′ eutectics to about 4-fold associated with severe microsegregation in interdendritic spaces. Ta addition elevated the γ′ solvus and solidus temperatures around 41°C and 25°C respectively and minimized the solidification range from 114°C to 52°C. Massive elimination of γ/γ′ eutectic and primary γ′ occurred in alloys solution annealed at 1230°C/4h. With increasing the solidification rate from 0.4 to 1.2°C/s remained γ/γ′ eutectic size was reduced about 85% in CM247 LC and 60% in Ta-modified CM247 LC after solutioning treatment. Secondary γ′ volume fraction raised from 36 to 49% in CM247 LC and from 52 to 60% in Ta-modified CM247 LC after aging. A critical solidification rate followed by a stepwise solutionizing treatment as 1230°C/4h+1250°C/2h+1260°C/2h+AC was proposed to minimize incipient melting areas and remained γ/γ′ eutectic size after solutionizing treatment combined with a maximum γ′ volume fraction for Ta-modified CM247 LC superalloy.

Effects of Mould Rotation on Element Segregation and Compact Density of Electroslag Ingots during Electroslag Remelting Process

AbstractSteel solidification process control, especially in the solidification process of high-alloy steel, and improving the solidification structure have been increasingly gaining interest among metallurgists, particularly the electroslag workers. To further develop the electroslag remelting (ESR) process and to improve the ingot solidification structure, the effects of mould rotation on chemical element distribution and the compact density were investigated in this study. The experimental results showed that chemical element distribution would become more uniform when the mould keeps the reasonable rotation rate. However, the excessive rotation rate would deteriorate the solidification structure of steel. When mould rotation rate was between 0 and 28 r/min, maximum segregation of carbon could decrease from 3.19 to 1.084, and statistical segregation decreased from 0.2636 to 0.0554. Maximum segregation of chromium could decrease from 1.316 to 1.131, and statistical segregation decreased from 0.2753 to 0.0657. The compact density increased from 0.7693 to 0.94. But element segregation would become bigger and compact density would become smaller if rotation rate further increased. The improvement in the solidification structure could be attributed to reasonable mould rotation rate which could initiate movement in the slag pool and further increase the uniformity of the temperature in the slag pool. At the same time, the movement in the slag pool could also affect the metal molten droplet, scattering the liquid drop randomly in the metal pool. But the excessive rotation rate made the slag pool violent motion, so as to drive the molten metal pool to rotate which would carry off enriched steel surrounding the dendrites in the mushy zone and reduce the solute content in the region. As a result, the element segregation would occur.

Control of Solidification Process and Surface Microstructure of Large Size Ingot ZALCu5MnA Alloy

Compared with conventional ingot, difficulties in melting and casting of large size ZALCu5MnA alloy is due to the increase of ingot size, which lead to a depth increase in smelting bath process, mixing melting liquid is also difficult, and chemical composition of molten pool is not uniform. this paper uses finite element method to analyze the temperature field and thermal stress field of large size ingot of alloy in solidification process, heat transfer model, radiation the boundary condition and latent heat of solidification processing are discussed meanwhile the microstructure of the casting parts surface and center are related researched.

Effects of Combination of 0.02 wt % Sr and Ti on the Characteristics of AC4B Alloys Produced by Low Pressure Die Casting

Aluminium AC4B alloy is widely used in automotive industries for various components. However, when this alloy is used to produce motorcycle cylinder head by Low Pressure Die Casting (LPDC) process, high reject rate was often found due to shrinkage, porosity and misrun. Addition of grain refiner and modifier is an alternative for this problem, through the control of solidification process that results in grain refining and microstructure modification. This study was aimed to investigate the effect of combination of 0.02 wt. % Sr modifier with variation of Ti grain refiner on the characteristics of AC4B alloy and the reject rate of cylinder head components. The Ti grain refiner was varied 0.063, 0.083 and 0.108 wt. % Ti and added at the holding furnace prior to LPDC process. A series of test was conducted including hardness test from the thin and thick regions of the part, tensile test, fluidity test, vacuum test as well as observation of microstructure by using optical microscope and Scanning Electron Microscopy (SEM) equipped with Energy Dispersive X-Ray Analysis (EDAX). The results showed that the higher the Ti content, the higher the hardness for both thin and thick areas, the lower the fluidity of the molten metal. At the maximum level of Ti of 0.108 wt. % and 0.02 wt. % Sr, the reject rate was significantly reduced from 3.59 % to 1.38 %.

Effects of relative motion between consumable electrodes and mould on solidification structure of electroslag ingots during electroslag remelting process

Steel solidification process control, especially in the solidification process of high alloy steel, and improvement of the solidification structure have been increasingly gaining interest among metallurgists, particularly the electroslag workers. To further develop the electroslag remelting (ESR) process and to improve the advantage of the ingot solidification structure, the effects of relative motion between the consumable electrodes and the mould (namely, mould rotation) on chemical element distribution were observed in this study, as well as the compact density changes in electroslag ingots. Experiment results show that applying relative motion between the mould and the consumable electrodes in ESR results in a more uniform chemical element distribution in the electroslag ingots. Compared with the electroslag ingot of conventional ESR, maximum segregation of carbon could decrease from 3·19 to 1·146, and statistical segregation decreased from 0·2636 to 0·0608. Maximum segregation of chromium could decrease from 1·316 to 1·253, and statistical segregation decreased from 0·2753 to 0·1201. The compact density for the stationary mould increased from 0·7693 to a compact density of 0·9501 for the rotating mould. The improvement in the solidification structure of the electroslag ingot can be attributed to mould motion, which led to the generation of a shallow pool and the improvement of the solidification structure. But the excessive rotation rate is harmful to solidification structure instead due to the molten metal pool motion caused by violent slag pool motion.

Determination of the effective distribution coefficient (K) for silicon impurities

For the production of photovoltaic cells, the silicon purity can be intermediate between metallurgical grade silicon (MG-Si, 98%–99.9% pure) and electronic grade silicon (>99.9999% pure). This silicon, with intermediate purity and that still meets solar cell requirements, is called upgraded metallurgical grade silicon (UMG-Si). One method of producing UMG-Si is applying a controlled solidification process, like unidirectional solidification (heat exchange method), zone melting (or zone refining), or Czochralski growth to MG-Si. These processes use the impurities solubility difference in solid and liquid silicon known as effective distribution coefficient (K). For these reasons, to study the solidification process, it is necessary to determine K for silicon impurities, which is the objective of this study. MG-Si (99.85% purity or 1500 ppm of impurities) was processed by 1 pass of zone melting at 1 mm/min using an electron beam furnace with water cooled copper crucible. The effective distribution coefficient (K) for impurities with Ko ≤ 10−1 was found to follow the relation K = 0.03 Ko−0.063. For boron, K = 0.8. Impurities with Ko between 10−3 and 10−8 presented similar effective distribution coefficients (K = 0.07 ± 0.02), meaning that the effective distribution coefficient of a specific impurity depends on the total amount of impurities. The measured impurities profiles in silicon were compared with those obtained by Pfann’s equations using the effective distribution coefficients and showed comparative results.

Theoretical and Practical Aspects Regarding Al-SiC Particles Composites Obtaining by Casting

The paper presents the principal aspects regarding the obtaining of the mixture aluminium - silicon carbide particles. It is discussed about the wetting conditions and the critical acceleration necessary for the incorporation of particles into the melt. The high values obtained for this parameter involve applying some methods to improve the wettability: the covering of the complementary material with a thin layer of Ni, the alloying of the aluminium melt, the overheating of the metallic bath and the heat treatment of the silicon carbide particles. Also, the mechanical stirring conditions necessary to realize the mixture are presented. The settling process of the silicon carbide particles in the melt as a function of particles size, shape and volumetric concentration is also analysed. The presence of complementary material leads to the growth of the mixture viscosity. Therefore, the liquid alloy was investigated like a continuous medium in connection with the apparent viscosity. The main aspects regarding the solidification of metallic composites processed by casting method based upon theoretical concepts, general knowledge about casting of composites and experimental data are discussed. Finally, the specific defects caused by an insufficiently controlled solidification process and prevention measures are shown.

Numerical modeling of the coupled electromagnetic and thermal fields in the controlled solidification process

PurposeThe purpose of this paper is to present the numerical modeling of the coupled electromagnetic and thermal fields for the controlled solidification process of non‐ferrous alloys.Design/methodology/approachThe paper uses a numerical modeling program for the controlled solidification process modeling to allow visualization of the model and collection of the data. The data are then processed using spreadsheets in order to obtain graphic representations for the variations of the measured values.FindingsThe probes cast using this method will have a uniform structure, without micro‐fissures. If the solid part growth of the molten is controlled, the process can be stopped that creates solidification centers, thus the material structure will be homogenous. A solution for this matter is given by the control of the solidification structure using forced heating of the liquid part with eddy currents and forced cooling of the solid part. The evolution of the area with eddy currents and the cooled one controls the phase transformation.Originality/valueIt is presented here a computation method for the thermal field diffusion and the results of the numerical modelling of the thermal and electromagnetic fields during casting process with controlled solidification layer for the non‐ferrous alloys.

Fixed Grid Simulation of Radiation-Conduction Dominated Solidification Process

In this paper conduction-radiation controlled solidification process of semitransparent materials was numerically analyzed. New approach in this kind of simulations, which is based on the fixed grid front tracking method combined with the immersed boundary technique, was adopted and examined. The presented method enables accurate dealing with solidification processes of semitransparent materials which have different optical and thermophysical properties of solid and liquid phases as well as with absorption, emission, and reflection of the thermal radiation at the solid-liquid interface without applying moving mesh methods. The proposed numerical approach was examined by solving several simplified thermal radiation problems with complex fixed and moving boundaries both in two-dimensional and axisymmetric spaces. For some of them the accuracy of obtained results was proved by comparing with reference works, other showed capabilities of the proposed method. For simplified solidification processes of semitransparent materials three configurations of optical properties, i.e., semitransparent solid phase and opaque liquid phase, opaque solid phase and semitransparent liquid phase, and semitransparent both phases were considered. The interface between solid and liquid phases was treated to be opaque, absorbing, emitting, and reflecting diffusely the thermal radiation. Results of the numerical simulations show that the presented numerical approach works well in this kind of problems and is promising for simulation of real solidification processes of semitransparent materials.

Process Development of Low-Cost AgNi and AgFe Contact Materials with no Range of Solid Solubility

AgNi and AgFe are known as contact materials with high workability and low contact resistance for medium to weak current contacts. However, AgNi and AgFe contact materials are difficult to manufacture using conventional melting and casting procedure because they exhibit no range of solid solubility of Ni and Fe in Ag for all temperature range. The purpose of this research is to develop a process for low-cost AgNi and AgFe contact materials based on solidification process control. AgNi and AgFe contact materials were produced by rotation cylinder method (RCM). The hardness value of AgNi and AgFe contact materials by RCM were higher than that of AgNi and AgFe contact materials produced by conventional powder metallurgy and co-precipitation processes. The higher hardness values of contact materials produced by RCM may be attributed to the uniform distribution and small size of Ni and Fe particles in Ag matrix.

Numerical modeling of the controlled solidification process

PurposeThis paper aims to present a numeric modeling of the electromagnetic and thermal phenomena for the non‐ferromagnetic alloys casting equipment that control the solidification structure's formation.Design/methodology/approachThe paper uses a numerical modeling program for the controlled solidification process modeling to allow visualization of the thermal field variation.FindingsThe probes cast using this method will have a uniform structure, without micro‐fissures. If the solid's part growth of the molten is controlled, we can stop the process that creates solidification centers, thus the material structure will be homogenous. A solution for this matter is given by the control of the solidification structure using forced heating of the liquid part with eddy currents and forced cooling of the solid part. The evolution of the area with eddy currents and the cooled one controls the phase transformation.Originality/valueThe paper presents a procedure to solve the coupled electromagnetic and thermal field problem in the casting systems techniques: solidification with controlled phase variation layer.

Process Development for Cost-Effective Ag-Ni Contact Materials by Simple Solidification Control

Ag-Ni is well known as contact materials with high workability and low contact resistance for medium to weak current contacts. However, Ag-Ni contact materials are difficult in controlling the Ni content, because Ag-Ni alloys exhibit no range of solid solubility of Ni in all temperature range. The purpose of this research is to develop a process for cost-effective Ag-Ni contact materials based on simple solidification control. The hardness of Ag-Ni contact materials produced by simple solidification control was higher than that of Ag-Ni contact materials produced by conventional powder metallurgy and coprecipitation method. The higher hardness value of contact materials produced by simple solidification control may be attributed to the uniform distribution and small size of Ni particles in Ag matrix. The properties of produced contact materials can be further improved by solidification process control.

Simulation and Control of Solidification Processes

The subject of studies was the process of casting a copper blast furnace tuyere. The investigation covered both physical and simulation experiments.The investigations described in this study enable obtaining, among others, the required distributions of temperature fields and the development of procedures aiding the solidification process control. The parameters detennining the heat transfer process course were measured. The obtained experimental data can be used as basis for simulation of the solidification process and for development of proper control procedures, the fmal aim of which is obtaining homogeneous temperature distributions at various points of a casting.

Preparation of poly‐si by excimer laser annealing with solidification process control

AbstractPolycrystalline silicon (poly‐Si) recrystallized by a conventional excimer laser has a small grain of about a few hundred Å and a mobility of about 100 cm2/Vs at most. It is believed that such small grain size could be due to a fast solidification velocity based on the authors's study of the solidification control of molten Si. A thermal analysis by computer simulation indicates that the solidification velocity can be lowered by heating substrate (400°C) during laser irradiation and thinning an amorphous Si (a‐Si) film (500 Å).Poly‐Si with a large grain (5000 Å) and high mobility (280 cm2/Vs) has been fabricated by excimer laser annealing in the present study. Nonuniformity of characteristics of poly‐Si in an overlapping region of the laser spot also is examined. An uncompleted melting of a mixed region of fine poly‐Si and a‐Si generated at an excimer laser spot edge is the cause for such nonuniformity. An overlapping region of a laser spot is found to become very uniform by using the present solidification control method. Nonuniformity of mobility is improved from ±20 to ±8 percent in the present study. This method is a very useful low‐temperature processing for fabricating large‐sized poly‐Si films.