Cu-rich precipitates formation is associated with the precipitation hardening of Fe-Cu based steels and the embrittlement of reactor pressure vessel steels under neutron irradiation. The accurate ...modeling of the time evolution of Cu-rich precipitates is therefore of fundamental importance for the design of Fe-Cu based steels and the prediction of the irradiation induced shift of the ductile to brittle transition temperature of reactor pressure vessels. This work applies cluster dynamics with mobile Cu monomers and clusters to model Cu precipitation in dilute Fe-Cu alloys at several temperatures. Optimized model parameters can be used to simulate the mean radius, number density, volume fraction, and matrix composition evolution during isothermal annealing with reasonable accuracy. The possible reduction of the mobility of Cu-rich clusters due to additional alloying elements in Fe-Cu based steels is discussed.
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•Extension of Slezov et al.'s cluster dynamics theory with cluster mobility•Effects of model parameters of the new model on precipitation kinetics•Accurate modeling of the Cu precipitation in Fe-Cu dilute alloys•Discussion of impurity effects on Cu precipitation kinetics
The microstructural evolution of Fe-6.5 wt.% Si alloy during rapid solidification was studied over a quenching rate of 4 × 104 K/s to 8 × 105 K/s. The solidification and solid-state diffusional ...transformation processes during rapid cooling were analyzed via thermodynamic and kinetic calculations. The Allen-Cahn theory was adapted to model the experimentally measured bcc_B2 antiphase domain sizes under different cooling rates. The model was calibrated based on the experimentally determined bcc_B2 antiphase domain sizes for different wheel speeds and the resulting cooling rates. Good correspondence of the theoretical and experimental data was obtained over the entire experimental range of cooling rates. Along with the asymptotic domain size value at the infinite cooling rates, the developed model represents a reliable extrapolation for the cooling rate > 106 K/s and allows one to optimize the quenching process.
•New Fe-6.5 wt.% Si melt spinning experiments and cooling rate measurements.•The melt spun ribbons were characterized using TEM analysis.•Solidification and solid-state transformation during rapid quenching were analyzed.•The bcc_B2 domain growth was modeled using the Allen-Cahn theory.
Irradiation-induced formation of Cu-rich precipitates embrittles reactor pressure vessel steels. In the present work, a cluster dynamics model is used to model the precipitation of Cu-rich ...precipitates in Fe–Cu and Fe–Cu–Mn model alloys under neutron and electron irradiation at about 300 °C (573 K). The model includes radiation-enhanced diffusion and mobile Cu-rich clusters, which have been suggested to play important roles in Cu precipitation kinetics in Fe-based alloys. Precipitation at low temperatures is accelerated by radiation-enhanced diffusion, due to excess vacancies produced by displacement damages. Previous modeling work of thermal precipitation in Fe–Cu alloys at higher temperatures suggests that Cu clusters are mobile, and that this mobility must be accounted for to predict the observed precipitation kinetics. Here, the present work extends the mobile cluster model to treat precipitation in Fe–Cu and Fe–Cu–Mn alloys under neutron and electron irradiation. Comparison of the properly parameterized model predictions with the experimental observations shows that treating radiation-enhanced cluster mobility is necessary to predict Cu precipitation kinetics under irradiation. The developed precipitation model can reasonably describe the selected reliable experimental data. The model parameter determination for the physically based model includes extensive sensitivity studies, and suggests that the present approach still needs refinement to provide an accurate model that is fully consistent with the known microscopic measurements.
Thermodynamic modeling of the Si-P and Si-Fe-P systems was performed using the CALculation of PHAse Diagram (CALPHAD) method based on critical evaluation of available experimental data in the ...literature. The liquid and solid solutions were described using the Modified Quasichemical Model accounting for the short-range ordering and Compound Energy Formalism considering the crystallographic structure, respectively. In the present study, the phase boundaries for the liquidus and solid Si phases of the Si-P system were reoptimized. Furthermore, the Gibbs energies of the liquid solution, (Fe)
(P,Si)
, (Fe)
(P,Si)
, and (Fe)
(P,Si)
solid solutions and FeSi
P
compound were carefully determined to resolve the discrepancies in previously assessed vertical sections, isothermal sections of phase diagrams, and liquid surface projection of the Si-Fe-P system. These thermodynamic data are of great necessity for a sound description of the entire Si-Fe-P system. The optimized model parameters from the present study can be used to predict any unexplored phase diagrams and thermodynamic properties within the Si-Fe-P alloys.
Precipitation is a natural phenomenon that is known to play an important role in the strengthening of Al–Li alloys. Cluster dynamics is powerful and effective in modeling the precipitation kinetics ...of precipitates in heat-treatable metallic materials, especially in the early stage. In this work, a cluster dynamics model with cluster mobility is further developed by redefining the effective monomer diffusivity for self-consistently modeling multicomponent and multiphase precipitation. The precipitation kinetic data for Al3Sc in Al–Sc binary alloys and Al3Li in Al–Li binary alloys are systematically reviewed and evaluated. The metastable fcc_A1/Al3Li two-phase equilibria are reoptimized using the split four sublattice compound energy formalism to accommodate both the related phase equilibrium measurements and precipitation kinetic measurements. One set of precipitation kinetic parameters is respectively assessed for each of the two precipitate phases. The improved cluster dynamics model, together with the assessed model parameters, can reasonably reproduce the reliable experimental precipitation kinetic data of the two phases. The model parameter determination includes extensive sensitivity studies to use physically reasonable values, and the present work also studies the use of cluster mobility in modeling the early stage precipitation kinetics. The present work indicates that the obtained model parameters can be used to develop the fundamental informative CALPHAD-type precipitation kinetic database.
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•Improved cluster dynamics model with cluster mobility for multicomponent and multiphase precipitation.•Newly defined effective monomer diffusivity for both diffusion-limited and kinetic-limited growth.•Critical review and assessment of Al3Sc and Al3Li precipitation kinetic data in binary alloys.•Cluster dynamics precipitation kinetic parameters for Al3Sc and Al3Li in binary alloys.•Discussion of precipitation kinetic database development in the frame of CALPHAD approach.
This work presents a complete review of the literature on and a critical evaluation and thermodynamic optimization of the Li-Se and Na-Se binary systems. The modified quasi-chemical model in the pair ...approximation (MQMPA) was employed to describe the liquid solution exhibiting a high degree of short-range ordering behavior of atoms. The thermodynamic properties of the compounds Li2Se (cF12_Fm3¯m), Na2Se (cF12_Fm3¯m), NaSe (hP8_P63/mmc), and NaSe2 (tI48_I4¯2d) were also calculated by using first-principles density functional theory (DFT) calculations to assist the thermodynamic description of these two binary systems. All the available and reliable experimental data are reproduced within experimental error limits. Moreover, the phase equilibria of these two systems at low total pressure were analyzed by using the developed thermodynamic model.
Reduction–sulfurization smelting is an effective method for treating solid hazardous waste and recovering valuable components from them. In this work, a waste hydrogenation catalyst (WHC), an ...automotive exhaust purifier waste catalyst (AEPWC), a vulcanizer, and laterite nickel ore were mixed, and the reduction smelting behavior of this solid waste was investigated. XRD (X-ray diffractometry), TG-DSC (thermogravimetric/differential scanning calorimetry), SEM-EDS (scanning electron microscopy-energy dispersive spectroscopy), OM (optical microscopy), and ICP-OES (inductively coupled plasma-optical emission spectrometry) methods were used to examine the chemical composition, thermal stability, structure, and morphology, as well as the metal content of the samples. Under the Al2O3-FeO-SiO2 ternary slag system, at a smelting temperature of 1450 °C, smelting time of 2 h, mass ratio of coke, pyrite, and CaO to waste catalysts of 16, 25, and 0%, respectively, nickel (Ni) and molybdenum (Mo) recovery reached 91.1 and 92.9%, respectively, where average PGMs (platinum group metals, platinum (Pt), palladium (Pd), rhodium (Rh)) recovery reached 96%, although vanadium (V) recovery was only 25.1%. The characterization of the slag shows that Al, Si, and Fe are mainly bound in the form of chemical compounds, while V is intercalated with ferro- or aluminosilicate, which hinders the reduction and sulfurization of V. A series of tests using reduction smelting without sulfurization were also conducted, after which the Ni, Mo, and V recovery reached 96.8, 96.6, and 89.7%, respectively, while PGMs (Pt, Pd, Rh) recovery ranges from 90.2 to 98.0%. The collaborative disposal of primary ore and multisource solid waste has been achieved through two process paths: reducing smelting and reducing sulfurization smelting, which provide reference for the collaborative smelting of multisource secondary resources.
An atomic mobility database for binary disordered and ordered fcc phases in multicomponent Al-Cu-Fe–Mg-Mn–Ni–Si–Zn alloys was established based on a critical review of diffusion data in various ...constituent binary systems via the DICTRA (DIffusion Controlled TRAnsformation) software package. The mobility parameters for self-diffusion in the metastable fcc structure were determined through a semi-empirical method. An effective strategy, which takes the homogeneity range and defect concentration into account, was used to optimize the atomic mobilities of L1
phase in the Fe–Ni system. Comprehensive comparisons between various calculated and measured diffusivities show that most of the experimental data can be well reproduced by the presently obtained atomic mobilities. The general agreement between the model-predicted concentration profiles and the experimental ones in the Al-Ni–Si, Al-Mg-Zn and Cu-Mn–Ni–Zn diffusion couples validates the potential application of the present atomic mobility database to predict the concentration profiles in higher order systems. An 8-elemental diffusion couple was also simulated with the present database.
Knowledge of diffusivity is a prerequisite for understanding many scientific and technological disciplines. In this paper, firstly major experimental methods, which are employed to provide various ...diffusivity data, are briefly described. Secondly, the fun-damentals of various computational methods, including first-principles method, embedded atomic method/molecular dynamic simulation, semi-empirical approaches, and phenomenological DICTRA technique, are demonstrated. Diffusion models re- cently developed for order/disorder transitions and stoichiometric compounds are also briefly depicted. Thirdly, a newly estab- lished diffusivity database for liquid, fcc_A1, Lie, bcc_A2, bcc_B2, and interrnetallic phases in the multicomponent A1 alloys is presented via a few case studies in binary, ternary and quaternary systems. And the integration of various computational techniques and experimental methods is highlighted. The reliability of this diffusivity database is validated by comparing the calculated and measured concentration profiles, diffusion paths, and Kirkendall shifts in various binary, ternary and quaternary diffusion couples. Next, the established diffusivity databases along with thermodynamic and other thermo-physical properties are utilized to simulate the microstructural evolution for Al alloys during solidification, interdiffusion and precipitation. A spe- cial discussion is presented on the phase-field simulation of interdiffusion microstructures in a series of Ni-Al diffusion couples composed of γ, γ＇, and β phases under the effects of both coherent strain and external compressive force. Future orientations in the establishment of next generation of diffusivity database are finally addressed.
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