Simulation Of Phase Transformations Research Articles

Ab Initio Molecular Dynamics Insight to Structural Phase Transition and Thermal Decomposition of InN.

Extensive ab initio density functional theory molecular dynamics calculations were used to evaluate stability conditions for relevant phases of InN. In particular, the p-T conditions of the thermal decomposition of InN and pressure-induced wurtzite-rocksalt solid-solid phase transition were established. The comparison of the simulation results with the available experimental data allowed for a critical evaluation of the capabilities and limitations of the proposed simulation method. It is shown that ab initio molecular dynamics can be used as an efficient tool for simulations of phase transformations of InN, including solid-solid structural transition and thermal decomposition with formation of N2 molecules. It is of high interest, because InN is an important component of epitaxial quantum structures, but it has not been obtained as a bulk single crystal. This makes it difficult to determine its basic physical properties to develop new applications.

MODELING OF PHASE TURNING PID HOUR OF PERMANENT COOLING OF HIGH-CARBON ALLOYING STEELS

On the basis of the author's analytical model together with finite element models, simulation of phase transformations during continuous cooling of high-carbon alloyed steels, intended for the manufacture of metal products of responsible purpose, in particular for the metallurgical and machine-building industries, was performed. The simulation results are summarized by constructing thermokinetic diagrams of austenite decay in the process of continuous cooling of steels 65Cr3SiMoV, 80Cr3MoV, 80Cr5MoV. The obtained results will be used during the adjustment of industrial modes of heat treatment of metal products of responsible purpose, in particular, back-up rolls of rolling mills. At the next stage of research, it is advisable to construct isothermal and structural diagrams of steels 65Cr3SiMoV, 80Cr3MoV, 80Cr5MoV including the determination of the distribution of structural components according to the depth of the strengthened layer (0–100 mm), which will allow to create scientifically based principles for improving the technology of heat treatment of support rolls rolling mills, which are made of high-carbon alloy steels.

Modelling the Evolution of Phases during Laser Beam Welding of Stainless Steel with Low Transformation Temperature Combining Dilatometry Study and FEM

In this study, the evolution of volume fractions during laser beam welding (LBW) of stainless steel, with a specific focus on incorporating the low transformation temperature (LTT) effect using the dilatometer, has been proposed. The LTT effect refers to the phase transformations that occur at lower temperatures and lead to the formation of a martensitic microstructure, which will significantly influence the residual stresses and distortion of the welded joints. In this research, the LTT conditions are achieved by varying the Cr and Ni content in the weld seam by varying the weld parameter, including laser power, welding speed and filler wire speed. The dilatometer analysis technique is employed to simulate the thermal conditions encountered during LBW. By subjecting the stainless steel samples to controlled heating and cooling cycles, the kinetics of the volume fractions can be measured using the lever rule and empirical method (KOP and Lee). The phase transformation simulation model is computed by integrating the thermal and metallurgical effects to predict the volume fractions in LBW joints and has been validated using dilatometer results. This provides valuable insight into the relationship between welding parameters and phase transformations in stainless steel with the LTT effect during laser beam welding. Using this relationship, the weld quality can be improved by reducing the residual stresses and distortion.

Evaluation of Austenite-Ferrite Phase Transformation in Carbon Steel Using Bayesian Optimized Cellular Automaton Simulation.

Austenite-ferrite phase transformation is a crucial metallurgical tool to tailor the properties of steels required for particular applications. Extensive simulation and modeling studies have been conducted to evaluate the phase transformation behaviors; however, some fundamental physical parameters still need to be optimized for better understanding. In this study, the austenite-ferrite phase transformation was evaluated in carbon steels with three carbon concentrations during isothermal annealing at various temperatures using a developed cellular automaton simulation model combined with Bayesian optimization. The simulation results show that the incubation period for nucleation is an essential factor that needs to be considered during austenite-ferrite phase transformation simulation. The incubation period constant is mainly affected by carbon concentration and the optimized values have been obtained as 10-24, 10-19, and 10-21 corresponding to carbon concentrations of 0.2 wt%, 0.35 wt%, and 0.5 wt%, respectively. The average ferrite grain size after phase transformation completion could decrease with the decreasing initial austenite grain size. Some other parameters were also analyzed in detail. The developed cellular automaton simulation model combined with Bayesian optimization in this study could conduct an in-depth exploration of critical and optimal parameters and provide deeper insights into understanding the fundamental physical characteristics during austenite-ferrite phase transformation.

“Anomalous” diffusion in multi-layer silicide systems

The transition metal silicide coatings have excellent oxidation resistance. In the high-temperature oxidization environment, the “anomalous” diffusion phenomenon of the reverse concentration gradient occurs in the multilayer silicide coating structure, which has a significant impact on the coating degradation. This study is to explore the physical mechanism of “anomalous” diffusion phase transformation in the MoSi2–NbSi2 bilayer silicide coating on the Nb alloy substrate. Through vacuum annealing experiments, combined with micro-Raman spectroscopy and electron probe microanalysis measurements, the diffuisonal phase transformation of multilayer silicide coating in the oxygen-free environment at high temperatures was studied. By decoupling the oxidation and diffusion, the experiments indicate that high-temperature oxidation is not the dominant driving factor for the “anomalous” diffusion of atoms. The thermodynamic analysis reveals that the reduction in the nucleation barrier of the silicide-poor layer due to multicomponent solid solution and the non-uniform distribution of component chemical potential provide the driving force for the “anomalous” diffusion growth. Based on the diffusion kinetic modeling, the simulation of diffusion-controlled phase transformation in multilayer silicide coating was carried out, and the effect of tracer diffusion coefficients on the growth of the silicide-poor phase was analyzed. The research will have guiding significance for the recognition of failure mechanisms of silicide coating systems and performance improvement.

Modelling and Simulation of Composition and Mechanical Properties of High Entropy Magnesium-Based Multi Component Alloy

Magnesium alloys are high potential materials for application in the aerospace and automotive industries due to their lightweight properties. They can help to lower dead weight and fuel consumption to contribute to sustainability and efficiency. It is possible to achieve high specific strength and high stiffness of the alloys by varying compositions of alloying elements. Applications of magnesium are limited due to its low strength and relatively low stiffness. This research focuses on a recipe of multi component alloys of magnesium with varied percentages of Mg, Al, Cu, Mn and Zn obtained from literature and optimizes the percentage compositions to obtain for high specific strength and specific stiffness. Relationships among percentage constituents of the alloy components are examined in Matlab R2022b using multiple linear regression. Optimization is achieved using genetic algorithm to determine the specific strengths and stiffness. The resulting optimal alloy component percentages by weight are used for microstructure simulation of thermodynamic properties, diffusion and phase transformations of proposed alloy is done in MatCalc software version 6.04. Results show potential for improved mechanical properties resulting from disordered structure in the high entropy magnesium alloy. Future research should focus on production and characterization of the proposed alloy.

Effect of chemical composition and isothermal treatment time on the microstructure and mechanical properties of high-strength carbide-free bainitic steel

Recent works about the development of carbide-free bainitic (CFB) steels use chemical compositions that require too long isothermal treatments for the bainitic transformation, making it difficult their manufacture under industrial continuous annealing processes. The present work reports an approach for designing CFB steels based on a computer simulation of phase transformations as a function of chemistry. The effect of chemistry and isothermal bainitic treatment (IBT) time on the microstructure and mechanical properties of CFB steels are also investigated. Results show that CFB steels of third generation, containing about 96% of bainite, can be obtained from short IBT times, opening the possibility to obtain these steels under the said conditions.

Accounting for random character of recrystallisation and uncertainty of process parameters in the modelling of phase transformations in steels

ABSTRACT The problem of multiphase microstructure heterogeneity was considered in this paper. The stochastic model of multi-step hot deformation was applied to calculate histograms of the dislocation density and the grain size at the beginning of phase transformations. These histograms were used as input data for simulation of phase transformations using conventional deterministic modelling. Heterogeneity of the phase composition was calculated for various constant cooling rates, as well as for the industrial laminar cooling process. In the latter case, uncertainty of the boundary conditions was additionally accounted for. The results showing an influence of the heterogeneity of the dislocation density and the grain size on the microstructure heterogeneity in the final product can be considered reliable, because they are based on the material models, which were identified and verified experimentally in earlier publications. The effect of the uncertainty of the boundary conditions is presented in a qualitative manner only, and may be the subject of future research.

Low Temperature Welding Test and Numerical Simulation of Metallurgical Phase Transformation of Q460GJC Thick Plate

Low Temperature Welding Test and Numerical Simulation of Metallurgical Phase Transformation of Q460GJC Thick Plate

A Comparative Study of Deterministic and Stochastic Models of Microstructure Evolution during Multi-Step Hot Deformation of Steels.

Modern construction materials, including steels, have to combine strength with good formability. In metallic materials, these features are obtained for heterogeneous multiphase microstructures. Design of such microstructures requires advanced numerical models. It has been shown in our earlier works that models based on stochastic internal variables meet this requirement. The focus of the present paper is on deterministic and stochastic approaches to modelling hot deformation of multiphase steels. The main aim was to survey recent advances in describing the evolution of dislocations and grain size accounting for the stochastic character of the recrystallization. To present a path leading to this objective, we reviewed several papers dedicated to the application of internal variables and statistical approaches to modelling recrystallization. Following this, the idea of the model with dislocation density and grain size being the stochastic internal variables is described. Experiments composed of hot compression of cylindrical samples are also included for better presentation of the utility of this approach. Firstly, an empirical data describing the loads as a function of time during compression and data needed to create histograms of the austenite grain size after the tests were collected. Using the measured data, identification and validation of the models were performed. To present possible applications of the model, it was used to produce a simulation imitating industrial hot-forming processes. Finally, calculations of the dislocation density and the grain size distribution were utilized as inputs in simulations of phase transformations during cooling. Distributions of the ferrite volume fraction and the ferrite grain size after cooling recapitulate the paper. This should give readers good overview on the application of collected equations in practice.

Study of the peritectic phase transformation kinetics with elastic effect in the Fe–C system by quantitative phase-field modeling

A quantitative phase-field model developed for two-phase growth process (Folch and Plapp, 2005) is applied to the simulation of peritectic phase transformation in a Fe–C binary alloy system with elastic effects due to the misfit on the solid/solid interface. The model includes the anti-trapping current, elastic effect, and the quantitative model parameters estimated based on the thin-interface limit. The diffusion of carbon in the solid phases (i.e. δ and γ phases) has not been neglected and an appropriate free-energy functional has been developed such that there is no presence of any extra phase in the interface. The model’s behavior over a wide range of interface width has been studied and the effect of anti-trapping current and elastic effect on the phase transformation has been closely analyzed.

Molecular dynamics simulation of phase transformation and wear behavior of Ni35Al30Co35 high temperature shape memory alloy

Ni–Al–Co alloys as one of the ferromagnetic high-temperature shape memory alloys (HTSMA) are attractive in aerospace and defense applications, due to their high phase transition temperature range (400–700K), high recoverable strain and good machinability. However, the underlying physics for the phase transformation behavior of β single-phase and β+γ two-phase Ni–Al–Co ternary alloys remain unclear. In this work, molecular dynamics simulation of phase transition, pseudoelasticity (PE) and wear behavior of Ni35Al30Co35 alloy were analyzed using the EAM potential. It shows that Ni35Al30Co35 alloy has a high martensite start temperature of 825K and an austenite start temperature of 631K, respectively. After five thermal cycles, martensite and austenite start and finish temperatures are stable around 500K and 700K. The initial structure of Ni35Al30Co35 alloy at 1000K is identified as BCC (β phase) and FCC (γ phase) structure, transforming to L10 structure through martensitic transformation. Furthermore, PE of Ni35Al30Co35 alloy exhibits about a 9.1% recoverable strain under <001> oriented uniaxial tension tests and about a 6.6% recoverable strain under <001> oriented uniaxial compression tests at a temperature of 1200K, showing the potential used in extreme environment. Moreover, spherical indenters with a radius of 15 Å were used to investigate the wear behavior of Ni35Al30Co35 alloy under different temperature. It was found that the PE effect affects the frictional behavior during nano-scratching. Combining the effect of high temperature softening and phase transition PE, the wear rate increases nearly by 5.3% when the temperature rises from 300K to 1000K. Furthermore, the friction force curve obtained is consistent with the friction force curve obtained by simulation at 300K.

Phase-field Modeling and Simulation of Solid-state Phase Transformations in Steels

The phase-field method is used as a powerful and versatile computational method to simulate the microstructural evolution taking place during solid-state phase transformations in iron and steel. This review presents the basic theory of the phase-field method and reviews recent advances in the phase-field modeling and simulation of solid-state phase transformations in iron and steel, with particular attention being paid to the modeling of the austenite-to-ferrite, pearlitic, bainitic, and martensitic transformations. This review elucidates that the phase-field method is a promising computational approach to investigate the microstructural evolutions (e.g., interface migration, solute diffusion, and stress/strain evolutions) that take place during the phase transformations. It also indicates that further improvements are required to enhance the predictive accuracy of the phase-field models developed to date. Finally, this review discusses the critical challenges and perspectives for the further improvement of the phase-field modeling of solid-state phase transformations in steel, i.e., the modeling of heterogeneous nucleation, the abnormal effect of the diffusion interface, and material parameter identification.

Consistent representation of vapor phases in phase field crystal dynamics

Accurate exploration of processes involving interactions among defects, voids, and density shrinkage in rapid solidification requires the ability to simulate phase transformations over large density ranges. We begin this work by presenting a number of numerical artifacts that arise in previous attempts to model the dynamics of solid-liquid-vapor interactions using phase field crystal (PFC) models based on a single density field coupled to its mean field. We then propose a new PFC formalism for modeling solid-liquid-vapor systems that self-consistently couples two components of the density field, one varying on the usual atomic length-scales, the other on scales much greater than the atomic lattice constant. It is shown that the new formalism is free of the aforementioned artifacts exhibited by previous PFC models. We generalize this new solid-liquid-vapor PFC model to alloys and demonstrate its utility through the nucleation of voids in both a fully solid material and during solidification into a liquid.

Phase-field modelling of mechanical wave propagation in polycrystalline materials: Validation study

With all the great advances in phase-field modelling combined with continuum mechanics, a detailed accuracy and convergence analysis about the influence of the diffuse interface upon the dynamic mechanical energy is still missing. Based on the previous work, i.e. deriving the homogenization scheme on the basis of balance conditions and embedding the high-order discontinuous Galerkin method into the phase field method, the influence of the diffuse interface, especially the multiphase/multigrain interface, on the dynamic mechanical energy is studied by considering the factors, such as the wave types, the material properties, the phase/grain size, the interface width and the normal vector formula. The numerical results are compared with the sharp-interface results to show the accuracy and stability, and with the linear homogenization method to demonstrate the advantages of the proposed scheme. The research work in this paper will build the foundation for the future simulation of rapid solid phase transformation.

Atomistic simulations of diffusive phase transformations with non-conservative point defects

Atomistic simulations of diffusive phase transformations with non-conservative point defects

Experimental evaluation and FE simulation of phase transformations and tensile stresses in hot forging and controlled cooling

Experimental evaluation and FE simulation of phase transformations and tensile stresses in hot forging and controlled cooling

Thermodynamic-Based Model Coupled with Phase Transformation Simulation to Predict the Ms Temperature in the Case of Two-Phase Steel

Thermodynamic-Based Model Coupled with Phase Transformation Simulation to Predict the Ms Temperature in the Case of Two-Phase Steel

Numerical Simulation and Experimental Analysis of Thermal Cycles and Phase Transformation Behavior of Laser-Welded Advanced Multiphase Steel

This work presents the results of the comparison between simulations and experiments of the laser welding of advanced multiphase steel. The numerical simulations of welding with different parameters were carried out using the Sysweld software. The geometry of the weld and structural constituents as well as stress distributions were analyzed. The simulated thermal cycles were incorporated in the JMatPro software to determine the phase transformation kinetics during cooling. The experimental tests were performed to compare the simulations with the real results. According to them, the shape of the weld and its width were symmetrical according to the weld axis. The simulated values were higher compared to the real one at heat inputs higher than 0.048 kJ/mm. The microstructure investigations conducted with scanning electron microscopy showed a good agreement in the fusion zone. Some differences in the microstructure of heat-affected zone and transition zone were identified. According to the phase transformation simulations, the weld should be composed of only martensite. The real microstructure was composed of martensite and some fraction of bainite in the heat affected zone. The more complex microstructure consisting of ferrite, bainite and retained austenite was present in the transition zone. The results of measured and simulated hardness indicated the good agreement with the difference of 17 HV0.1.

Nucleation of Grain Boundary Phases.

We derive a theory that describes homogeneous nucleation of grain boundary (GB) phases. Our analysis takes account of the energy resulting from the GB phase junction, the line defect separating two different GB structures, which is necessarily a dislocation as well as an elastic line force due to the jump in GB stresses. The theory provides analytic forms for the elastic interactions and the core energy of the GB phase junction that, along with the change in GB energy, determines the nucleation barrier. We apply the resulting nucleation model to simulations of GB phase transformations in tungsten. Our theory explains why under certain conditions GBs cannot spontaneously change their structure even to a lower energy state.