The microstructural features of as-cast alloys are predominantly influenced by the fabrication process, which eventually determine the properties. In the present work, we demonstrate that the ...microstructure (e.g., composition, phase constitution and distribution) and the magnetocaloric properties of the La(Fe,Si)13 alloys can be effectively tailored by tuning the solidification kinetics. La(Fe,Si)13 alloys with different dimensions were prepared by suction casting and jet casting. Finite element (FE) simulations reveal a difference in the temperature gradient along the solidification path of the rapid solidification process. The microstructure difference between the edge and center regions in the as-cast ingots along the solidification direction is increased for the samples with larger diameter. This can be attributed to the different solidification kinetics as predicted by the FE simulations. More homogeneous microstructure can be observed in the samples with a smaller size. The largest magnetic entropy change value of 16 J/kg·K can be obtained in thin plates, which is comparable to that of master bulk alloy. Our thorough study of solidification mechanisms during rapid solidification provides research basis for manipulating the microstructure homogeneity and the related properties, which also paves the way for the study of other rapid-solidificated materials.
•Samples with different parameter in this work are obtained by different preparation methods (suction casting and jet casting), intrinsically depending on the filling ability and solidification kinetics.•We demonstrate that the difference of the microstructure between the edge and center regions increases with the deeper heat diffusion path, which can be attributed to solidification kinetics and were analyzed by the Finite element (FE) simulations. This can explain degradation or remaining of magnetocaloric effect (MCE) for rapid-solidificated La(Fe,Si)13 alloy prepared by different reports.•More homogeneous microstructure (e.g., composition, phase constitution and distribution) can be observed in the samples with a smaller size. Thus, microstructure and related properties of the La(Fe,Si)13 alloys can be effectively tailored by tuning the solidification kinetics.
The rapid solidification mechanism of Ni–Zr alloys was investigated by electromagnetic levitation (EML) technique assisted with high speed videography. A systematic analysis of the competitive growth ...mode between the primary phase and eutectic structure was conducted for three types of alloys (hypoeutectic Ni-5 at.%Zr, eutectic Ni-8.8 at.%Zr and hypereutectic Ni-13 at.%Zr alloys), whose maximum undercoolings reached up to 260, 192 and 270 K, respectively. With the increase of undercooling, the primary (Ni) phase of hypoeutectic Ni-5 at.% Zr alloy transferred from well-defined dendrites to dendrite fragments. Zr atom was difficult to diffuse into the Ni lattice because the radius of Zr atom was larger than Ni atom. For eutectic Ni-8.8 at.% Zr alloy, the competitive nucleation and growth between primary (Ni) phase and eutectics could happen when the undercooling exceeded 18 K. The refined dendrites of primary (Ni) phase and various eutectic morphologies were observed at the undercooling of 192 K. For the hypereutectic Ni-13 at.% Zr alloy, the growth morphology transition of the primary Ni5Zr intermetallic compound from faceted to non-faceted crystals occurred if the liquid alloy achieved a high undercooling. Furthermore, the atomic scale structure of the primary phase was explored by the transmission electron microscopy (TEM), which revealed that the solid solubility and the lattice constant were consistent at various undercoolings. Moreover, the compressive performance of these three type alloys were determined for EML solidified samples. Due to the effects of undercooling and composition on microstructures, Ni-5 at.%Zr and Ni-8.8 at.%Zr alloys exhibited plastic deformation at the large strain condition, while Ni-13 at.%Zr alloy showed brittle fracture feature. The compressive strength and yield strength displayed a non-linear relationship with the rise of undercooling.
It is of great theoretical significance to study the solidification kinetics of metal materials for improving the microstructure and properties. In this paper, the Differential Scanning Calorimetry ...(DSC) was used to measure the enthalpy change of solidification process of 1035 steel at different cooling rates. The activation energy of the solidification process was determined by the equal conversion method based on the data of enthalpy. The mechanism function of the solidification process was also determined. It is shown that the value of the activation energy of solidification process varied with the solidification fraction, and the mechanism functions of solidification process are different in different temperature ranges, which are –ln(1– α) for 1 504-1 502 °C –ln(1–α)1/2 for 1 500-1 942 °C and –ln(1– α)2/5 for_1 490 °C respectively.
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A new coupled heat transfer and solidification kinetics model is developed for the optimization of microstructure during laser additive manufacturing applications. The ...Johnson–Mehl–Avrami–Kolmogorov equation is applied in a self-consistent manner for modeling of the rapid phase change on the substrate. The numerical simulations using the OpenFOAM framework are conducted for Ni-based superalloy single track laser cladding. Single track laser cladding experiments were carried out to verify the results of our calculations. A rather good coincidence with the experimental data is shown for the developed model. The influence of processing parameters on the macro and micro parameters of the tracks is analyzed. A method for changing the average crystalline size and simultaneous preservation of the height and width of the track is presented. The possibility of controlling the microstructure of similar tracks gives an opportunity to preserve the scanning strategy for building parts with a defined quality.
In this study we present the compositional changes of clinopyroxene (cpx), plagioclase (plg), spinel (sp), and glass experimentally solidified from an Icelandic MORB melt. The starting material was ...cooled at Patm and fO2 of air, in the thermal range of cooling (ΔTc) between 1300 °C (superliquidus) to 800 °C (solidus) with rates (ΔT/Δt) of 1, 7, 60, 180, 1800, and 9000 °C/h. The run products obtained at 1, 7 and 60 °C/h are holocrystalline, whilst between 60 and 180 °C/h plg disappears, and texture of cpx + sp. shifts from faceted to dendritic.
As cooling rate increases, we observe that Fe2O3 decreases and Al2O3 increases in sp. and Al2O3 + Fe2O3 increase and CaO + MgO decrease in cpx. These measured variations mirror changes induced by cooling rate in cation (atoms per formula unit, a.p.f.u.) and molecular abundances of these two crystalline phases. Plg composition shows clear linear trends versus cooling rate. The chemistry of sp., cpx and, to a minor extent, plg solidified from this basaltic liquid is thus strictly related to the cooling rate condition and is similar to those observed in previous investigations on alkaline and evolved basaltic systems. In particular, cpx is the only mineral phase profusely present at all the cooling rates, showing the greatest chemical variations in terms of oxides, cations, and components. The intra-crystalline glass (≤ 50 μm from crystal rims) obtained at 180–1800 °C/h shows compositional variations related to the surrounding crystal growth, evidencing strong supersaturation phenomena (such as dendritic texture) due to the establishment of a diffusion-controlled growth regime. Chemical attributes of mineral phases are also quantitatively related with the maximum (Gmax) and average (GCSD) growth rates of sp., cpx, and plg.
When compared with the starting melt composition, the chemistry of cpx suggests the attainment of near-equilibrium crystallization conditions at cooling rate ≤ 60 °C/h, whereas disequilibrium effects are found at cooling rate > 60 °C/h. In contrast, plg is in disequilibrium with the initial melt chemistry in all experiments. By using thermometric models, the calculated crystallization of plg takes place at temperatures much lower than those of cpx, when the crystal content is high and the diffusion of cations in the melt is slow due to the higher (residual) melt viscosity. Under such conditions and due to the effect of cooling, the system cannot return to homogeneous concentrations and, consequently, plg more effectively records the disequilibrium partitioning of cations between the growing crystal surface.
The data-set reported here captures the entire (superliquidus to solidus) and intrinsic (heterogeneous site-free silicate liquid) solidification behavior from an actual MORB melt from very rapid to extremely sluggish cooling rate. Finally, all analytical relationships found in this work enable careful reconstruction of the solidification conditions of MORB melts, providing novel geo-speedometers for them at high fO2.
•Dynamic solidification of a MORB liquid from 1 to 9000 °C/h.•Sp, cpx, and plg chemical changes as a function of cooling rate.•(Dis)equilibrium kinetics of crystallization provides geospeedometers.•Order of mineral segregation.•Crystal-chemical and textural variations are quantitatively related.
In this research, transient liquid phase (TLP) bonding of IN718 and SS316L dissimilar alloys was carried out using MBF-20 amorphous interlayer. The effects of bonding temperature and time ranging ...from 1030°C to 1110°C and 1-30 min on the microstructure and mechanical properties of the bonded samples were studied. The mechanism of the microstructure formation and the solidification sequence at the joint area were discussed. Two diffusion models assuming stationary and moving solid/liquid interface were used to study the isothermal solidification kinetics and the time required for the complete isothermal solidification (t
f
) at different temperatures was predicted. The results suggest that the t
f
values obtained by the moving interface approach are closer to those of the experiments. The minimum difference between the experimental value of t
f
and that calculated by the moving interface approach was about 26%, while it was about 106% by considering the stationary interface approach. A more uniform hardness distribution across the joint area and the highest shear strength values were observed in the samples with complete isothermal solidification. The maximum shear strength of 440 MPa was obtained for the sample bonded at 1030°C for 30 min. This was attributed to the formation of a eutectic-free joint in these samples.
•An analysis is performed close to the triple junction of horizontal ribbon growth.•The analysis predicts solid–liquid interface temperature and liquid supercooling.•The facet length and misalignment ...angle are accurately predicted by the analysis.•Accurate flow and thermal numerical simulations confirm the analytical model.
Horizontal ribbon growth (HRG), in which a thin sheet of solidified material is pulled horizontally from the surface of a molten pool, is proposed as an efficient technique for growth of single-crystal silicon sheets. Despite recent results, some details of the process are still not understood, in particular the solidification mechanism at the triple junction point (TJP) where the solid, the liquid, and the surrounding gas meet. The solidification mechanism in the HRG process is investigated in this paper both analytically and numerically, incorporating the solidification kinetics that lead to faceted growth. The conventional solid–liquid problem in the HRG process is formulated analytically in the vicinity of the triple junction point (TJP). The temperature distribution is obtained for the liquid and solid regions as a function of the underlying parameters of the HRG process, such as the material properties, the ribbon pull speed, and the cooling heat fluxes. Using the analytical results, the TJP temperature, the facet length, interfacial temperature gradients, and liquid supercooling can be predicted. The analytical formulation is validated against accurate numerical simulations of the same problem, showing a good agreement in predicting the temperature gradients and the facet growth. The findings of this study suggest that using the analytical model, the behavior of the solid ribbon and the existence of a supercooled region in the liquid in the HRG process can be predicted without the need for numerical simulations. The model also gives criteria for optimal performance of the HRG process.
Using the non-equilibrium molecular dynamics (NEMD) simulations and the time-dependent Ginzburg–Landau (TDGL) theory for solidification kinetics, we study the crystal-melt interface (CMI) kinetic ...coefficients for both the soft-sphere (SS) BCC-melt and the FCC-melt interfaces, modeled with the inverse-power repulsive potential (n=8). The collective dynamics of the interfacial liquids at four equilibrium CMIs are calculated and employed to eliminate the discrepancy between the predictions of the kinetic coefficient using the NEMD simulations and the TDGL solidification theory. The speedup of the two modes of the interfacial liquid collective dynamics (at wavenumbers equal to the principal and the secondary reciprocal lattice vector of the grown crystal) at the equilibrium FCC CMI is observed. The calculated local collective dynamics of the SS BCC CMIs are compared with the previously reported data for the BCC Fe CMIs, validating a hypothesis proposed recently that the density relaxation times of the interfacial liquids at the CMIs are anisotropic and material dependent. With the insights provided by the improved application of the TDGL solidification theory, an attempt has been made to interpret the variation physics of the crystal-structure dependence of the solidification kinetic coefficient.
A new approach is used to model transient liquid phase (TLP) bonding without the simplification assumption of one-dimensional solid-liquid interface migration. In contrast to the general assumption ...that the single parameter, Φ, that is often used to represent the isothermal solidification kinetics during TLP bonding is constant, this work reports for the first time by coupled numerical simulation and experimental verification that a condition exists where Φ becomes a variable parameter that increases with time. This unique isothermal solidification kinetics behaviour is attributable to a combination of two-dimensional migration of the solid-liquid interface and solute diffusion in a direction along the increase in radius of curvature.
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