Modeling Of Microstructure Evolution Research Articles

Parallel simulation via SPPARKS of on-lattice kinetic and Metropolis Monte Carlo models for materials processing

SPPARKS is an open-source parallel simulation code for developing and running various kinds of on-lattice Monte Carlo models at the atomic or meso scales. It can be used to study the properties of solid-state materials as well as model their dynamic evolution during processing. The modular nature of the code allows new models and diagnostic computations to be added without modification to its core functionality, including its parallel algorithms. A variety of models for microstructural evolution (grain growth), solid-state diffusion, thin film deposition, and additive manufacturing (AM) processes are included in the code. SPPARKS can also be used to implement grid-based algorithms such as phase field or cellular automata models, to run either in tandem with a Monte Carlo method or independently. For very large systems such as AM applications, the Stitch I/O library is included, which enables only a small portion of a huge system to be resident in memory. In this paper we describe SPPARKS and its parallel algorithms and performance, explain how new Monte Carlo models can be added, and highlight a variety of applications which have been developed within the code.

Microstructure evolution and constitutive modeling of as-cast A356 aluminum alloy in semi-solid deformation regime

The present work deals with the semi-solid deformation behavior of A356 aluminum alloys with an emphasis on microstructure evolution and constitutive modeling. The main idea of this research is based on investigating the semi-solid deformation behavior starting with primary dendritic cast structure, instead the conventional approach in which a feedstock is prepared through the various spheroidization process. Toward this end, hot compression tests in the semi-solid temperature range (580, 590, and 600 °C) under different strain rates (0.001, 0.01, 0.1 s−1) and different initial holding times (1, 7, and 14 min) have been conducted. Compared with the thixotropic deformation in which the solid globules slide within the liquid matrix through lubricated flow mechanisms, in the present case, the strain compensation through the deformation of solid grains was increased. The higher portion of the solid-grains from the applied strain provided a proper condition for substructure development and dynamic recrystallization in the semisolid temperature range. The penetration of the liquid phase along the newly developed boundaries was introduced as another factor influencing on the softening behavior of the material. Under these conditions, the specimens were deformed up to the high strain level (>0.5) without creating cracks or tearing under very low stresses less than 2 MPa. A phenomenological-physical constitutive equation was also developed considering deformation parameters (temperature, strain rate, and strain) and material's parameters (grain size, strain rate sensitivity, viscosity) which was capable of predicting the semisolid flow stress behavior of the material.

Phase field model of microstructure formation during cooling slope slurry generation of novel Al-15Mg2Si-4.5Si composite

The present study discusses the development of a two-dimensional phase field model of semi solid microstructure evolution of the novel Al-15Mg2Si-4.5Si composite during cooling slope rheoprocessing. The superheated melt of the said composite undergoes partial solidification during its shear flow over the slope free surface, prior to get collected within the isothermal slurry holding furnace. Seed undercooling based nucleation model is adopted in the present PF model to simulate slurry microstructure of the composite. Experimentally determined cooling rate values are considered to simulate slurry microstructure for different process conditions. Micrographs of melt samples collected during experimentation establishes the developed PF model as an accurate microstructure prediction tool for the composite slurry. Apart from morphological features such as size and degree of sphericity values of the evolving primary Mg2Si and α-Al grains, the model predictions includes melt temperature as well as solid content at any given instant of slurry processing.

Microstructure evolution of Pr-doped SmCo4B-based ribbons with improved magnetization

Searching for high-performance permanent magnets is always challenging for modern technological applications. The novel SmCo4B phase has a higher anisotropy field than SmCo5, and this paper disclosed the effect of Pr addition on the phase transformation, microstructure evolution, and magnetism of the multi-element doped Sm1−xPrxCo3.04Fe0.9Cu0.06B ribbons. The results show that Pr addition decreases the amorphous forming ability of the as-spun ribbons. After annealing, Pr addition promotes the growth of strip-like Sm-Co-B grains, and 8 at% Pr addition increases the saturation magnetization and remanence of the Sm-Co-B ribbons by 96.2% and 48.0%, respectively. Pr addition weakens the anisotropy field of the Sm-Co-B phase, resulting in a gradual decrease in coercivity. We revealed the transformation mechanism of strip-like grains during melt-spinning and annealing, found the relationship between phase content, dislocation density, strain, and grain size, and proposed the corresponding microstructure evolution models.

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.

Numerical prediction of microstructure evolution of high-speed railway axle formed using hot cross wedge rolling

The ununiform distribution of the grain size and coarse crystals is easy to be appeared in the high-speed railway axle (HSRA) formed by hot cross wedge rolling (CWR). It seriously reduces the comprehensive mechanical properties of the HSRA. It is vital to numerically predict microstructure evolution, so that the mixed and coarse crystals can be accurately controlled via process parameters optimization. In this study, the microstructure evolution model of the 40CrNiMo steel was developed and implemented into the DEFORM-3D software by programming a user subroutine to simulate hot upsetting. Microstructure of specimens after hot upsetting experiment was investigated to validate the finite element (FE) prediction model of microstructure evolution. The simulation results were close to the experimental results, which verifies that the established microstructure evolution model has a good predictability. The developed microstructure evolution model and the FE prediction system of hot CWR were used to simulate the forming of HSRA. Hot CWR simulations of HSRA was conducted at rolling temperature of 1000 °C and rolling sped of 1.5 r/min with initial grain size of 200um. Numerical prediction of dynamic recrystallization (DRX) volume fraction and average grain size in three segments of CWR, such as wedge entering segment, widening segment and finishing segment, were carried out to study the microstructure evolution of CWR. Results show that the maximum average grain size locates in the heart of hub axle section, which is smaller than grade 5 and above (d≤62.5μm). It indicates that the microstructure of HSRA after CWR meet the requirements of grain structure grade in international standard of EN13261. Effects of rolling temperatures, rolling speeds and initial grain sizes on the microstructure distribution after hot CWR were analyzed using FE simulations for 40CrNiMo steel. The rolling temperature of 1050 °C, rolling speed of 6 r/min and initial average grain size of less than 200μm are suggested to produce HSRA using CWR. Composite manufacturing processes, i.e. free forging plus hot CWR, are suggested to produce HSRA. The material saving as well as improving production productivity simultaneously become a reality. This provides a guiding reference for the actual production of HSRA.

Modelling of Mechanical Response and Microstructure Evolution of EA4T Steel during Hot Compression Using the Improved Crystal Plasticity Finite Element Method

Modelling of Mechanical Response and Microstructure Evolution of EA4T Steel during Hot Compression Using the Improved Crystal Plasticity Finite Element Method

Unified modeling of the microstructure and densification of TC4 powder titanium alloy during hot deformation

An accurate material constitutive model is very important to apply numerical simulation technology to predict, establish and optimize the thermoplastic forming process parameters of powder titanium alloy. To achieve this goal, the microstructure evolution and densification of TC4 powder titanium alloy were investigated during compression at temperatures from 860 °C to 960 °C, strain rates from 0.05 s−1 to 20 s−1 and strains from 0.357 to 1.204. The results show that the microstructure undergoes dynamic recrystallization under different conditions. High temperature, large deformation degree and low strain rate are helpful to reduce porosity, pore size and pore colony. Plastic deformation and diffusion are two main mechanisms of densification. The microstructure evolution and densification model were established, combining the power constitutive law, a unified constitutive model was proposed to predict flow stress, microstructure and relative density of TC4 powder titanium alloy. The model constants were determined through a genetic algorithm. The predicted values of flow stress and relative density agreed well with the experimental values. The variations in relative density with temperature, strain rate and strain were analyzed based on the prediction results.

Convoluted filtering for process cycle modeling

AbstractPrinciples of materials science and engineering, physics, mathematics, and information science are used to extract knowledge and insights from the process‐structure–property‐performance relationships hidden in materials data. The process‐structure modeling can be accelerated without loss of interpretability, with artificial intelligence tools that mimic the salient features of the process and process‐structure relations. In this work, a novel convoluted model‐filtering technique was exploited to build and successfully train the Convoluted Filter (CoFi) artifacts for Fe‐based alloy heat treatment cycles. The artifacts were pre‐trained to filter out deep models that change the surrogate microstructure state after the heat treatment at ambient conditions. Direct representation of the thermal cycle features within knowledge Graph facilitated development of meaningful data models for microstructure evolution, which reduce overfitting to limited datasets.

INVESTIGATING THE EFFECT OF HEAT TREATMENT ON THE COLD FORGING OF 27MNB4 STEEL VIA CALPHAD METHODOLOGY AND FEM

As a material forming method, cold forging is preferred due to the reasons like absence of a heating step and high surface quality. Recently, the finite element method (FEM) has received growing attention for controlling and predicting final material properties for cold forging applications. FEM combines microstructure evolution models with failure criteria, thus providing solutions to complicated problems in the modern cold forging industry. The fastener industry extensively utilizes cold forging, in which manganese and boron-containing steels like 27MnB4 can be formed to obtain high mechanical properties. The current study investigates the effect of two different heat treatments, namely softening and spheroidizing annealing, on the formability of 27MnB4 bolts. Softwares such as Thermo-Calc 2022a and Forge NxT 3.2 were used to predict the microstructure of the wire rod and evaluate the cold forming process of the same rod under two different heat treatment conditions. Therefore, the current study also provides a relationship between microstructural features and the cold formability of 27MnB4 steel. The microstructure of 27MnB4 is predicted by CCT diagrams. The predicted microstructure corresponds to the microstructure of 27MnB4 samples taken from the production line. In addition, temperature, von Mises stress, and equivalent strain distributions for 27MnB4 steel in the hot rolled state were calculated higher than in annealed states due to the differences in the microstructure. These results demonstrate that computational material engineering methods and simulation techniques could be practical tools for cold forming processes.

Correlated structure viscoplastic self-consistent polycrystal plasticity: Application to modeling strain rate sensitive deformation of Ti-6Al-4 V

This paper presents a multi-level viscoplastic self-consistent (VPSC) model for correlated structures (CS-VPSC). A polycrystalline aggregate response is homogenized over inclusions, which are linearized using the generalized affine scheme. Response of the inclusions is that of either a single grain or a correlated structure of multiple single crystals. The single crystal response is a strain rate adjusted power-law viscoplastic formulation, which considers not only the driving force in the glide direction but also the two orthogonal shear and three normal components of the driving force. The resistance to slip is grain size sensitive and based on the evolution of dislocation density. Furthermore, the resistances of prismatic and basal slip systems are adjusted based on the geometry of slip transfer between adjacent correlated structures. The overall model linking the single crystal micro-scale to a correlated structure meso‑scale to an aggregate macro-scale response is also coupled with the implicit finite elements (FE-CS-VPSC). The model is used for modeling strain rate sensitive mechanical response and microstructural evolution of additively manufactured Ti-6Al-4 V (Ti64) alloy in two conditions. As-built and stress-relived (SR) microstructure consisted of correlated α-lath/lamellar structures, while thermo-hydrogen refined microstructure (THRM) consisted primarily of α- and β-globular structures and some correlated α-lath/lamellar structures. Electron backscatter diffraction data, neutron diffraction data, and mechanical data were used to initialize, calibrate, and validate the model. To this end, the flow stress and texture evolution of the materials in tension and compression under quasi-static and high strain rate deformations were predicted using CS-VPSC, while the texture evolution during rolling and impact was simulated using FE-CS-VPSC. Good predictions of the texture evolution and mechanical response including the tension/compression asymmetry allowed us to discuss the roles of correlated structures, slip system activation stresses, size effects, strain partitioning between phases, and slip activities in such predictions.

Impact of uniaxial strain on oxygen monovacancy diffusion in uranium dioxide: A molecular dynamics study

Understanding defect diffusion kinetics in a strain field is essential for multiscale modeling of UO2 microstructure evolution, particularly in the case of creep, swelling, crack, etc. Although the diffusion kinetics of point defects in UO2 is well explored both experimentally and theoretically, the kinetics under strain conditions is not well understood. In the present study, the diffusion of oxygen monovacancy in UO2 subjected to uniaxial tensile strain as much as 3% in the directions of <100>, <110>, and <111> is investigated by means of molecular dynamics (MD) simulations in the temperature range of 600–1000 K. The results show that in the case of strain in <100> direction, diffusivity decreases with tensile strain, especially at high temperatures above 700 K. In contrast, diffusion is promoted with stretching in <110> and <111> directions. It is assumed that this may be the combined result of independent variation of migration energy (Em) and pre-factor (D0), according to the Arrhenius equation. Further investigations are made with nudged elastic bands (NEB) calculations for a better interpretation of the effect of directional strain on migration energy. It is found that the effect is anisotropic, and the variation of Em is in good agreement with that of MD calculations. Stretching along the <100> direction results in the decrease of Em in all three directions, with <100> the most profound. Stretching in <110> and <111> directions exert negligible effect. The present study provides insights into the effect of strain on the diffusion of oxygen vacancy in UO2, however, further research is needed for the effect of arbitrary strain on poly-crystalline UO2.

Deformation, dislocation evolution and the non-Schmid effect in body-centered-cubic single- and polycrystal tantalum

A physically-informed continuum crystal plasticity model is presented to elucidate deformation mechanisms, dislocation evolution and the non-Schmid effect in body-centered-cubic (bcc) tantalum widely used as a key structural material for mechanical and thermal extremes. We show the unified structural modeling framework informed by mesoscopic dislocation dynamics simulations is capable of capturing salient features of the large inelastic behavior of tantalum at quasi-static (10−3 s−1) to extreme strain rates (5000 s−1) and at low (77 K) to high temperatures (873 K) at both single- and polycrystal levels. We also present predictive capabilities of the model for microstructural evolution in the material. To this end, we investigate the effects of dislocation interactions on slip activities, instability and the non-Schmid behavior at the single crystal level. Furthermore, ex situ measurements on crystallographic texture evolution and dislocation density growth are carried out for polycrystal tantalum specimens at increasing strains. Numerical simulation results also support that the modeling framework is capable of capturing the main features of the polycrystal behavior over a wide range of strains, strain rates and temperatures. The theoretical, experimental and numerical results at both single- and polycrystal levels provide critical insight into the underlying physical pictures for micro- and macroscopic responses and their relations in this important class of refractory bcc materials undergoing large inelastic deformations.

Phase field modeling microstructural evolution of Fe-Cr-Al systems at thermal treatment

A phase field model to study dynamics of microstructure transformations and the evolution of defect structure during heat treatment of Fe-Cr-Al systems is developed. Statistical and kinetic properties of evolving microstructure and defect structure in alloys with different content of alloying elements and at different temperatures were studied. Point defects rearrangement during precipitation is discussed in details. Universality of statistical distributions over precipitate size is revealed for considered class of alloys.

Modeling and Simulation of Microstructural Evolution in Zr based Metallic Glass Matrix Composites (MGMC) in Additive Manufacturing - Ceramics Proposal

Modeling and Simulation of Microstructural Evolution in Zr based Metallic Glass Matrix Composites (MGMC) in Additive Manufacturing - Ceramics Proposal

Prediction Model for Microstructure Evolution of 610L during Hot Rolling Process

The microstructure evolution of steels through the whole process method can guide steel production at a lower cost. In this paper, the stress-strain curves of 610L under different deformation conditions are studied using a Gleeble-3500 testing machine. This work combines dynamic recrystallization, static recrystallization, and sub-dynamic recrystallization models to predict the recrystallization fraction and grain size during the rolling process. Through linear fitting, the parameters m1 , Q, and A are 0.15, 9030.19, and 0.062, respectively. Comparing the experimental results with the fitted model, it is found that the grain size calculated by the model is close to the experiment, proving the model’s accuracy.

Model Based Prediction of the Heat Affected Zone in a Steel Workpiece Induced by an EDM Single Discharge

Setting a determined microstructure within the rim zone of a manufactured workpiece without cost-intensive trial and error experiments is essential to meet the increasing requirements of the industry. The most promising approach to predict the final functional properties is to simulate the microstructure evolution and to build an inverse approach of the manufacturing process. Thermal load based microstructure evolution models with an artificial initial structure and temperature gradients up to 1·106 K/s have been published in previous works presented by the authors. In this work, an existing heat transfer model was extended to predict the actual temperature gradients for a single discharge during electrical discharge machining (EDM). These calculated temperature gradients were then used to simulate the microstructure evolution of a 42CrMo4 steel. The initial structure was derived from a cross sectional SEM image. Therefore, the presented model is able to simulate the actual microstructure evolution within the heat affected zone of an EDM'ed workpiece.

Study of growth kinetics of intermetallic compounds at BAl88Si/Cu interface

• The diffusion behavior of the elements at the interface is investigated. • The diffusion reactions of the interface are analyzed. • The growth kinetics of the interfacial compound are analyzed. • The interfacial microstructure evolution model of BAl88Si/Cu are established. In this study, the growth of the intermetallic compounds (IMCs) at the BAl88Si/Cu interface was analyzed and its growth kinetics was investigated. The results reveal that Cu 3 Al, Cu 9 Al 4 , Cu 3 Al 2 and CuAl, four-layer IMCs are formed at the interface due to the interdiffusion of copper elements and aluminum elements. The thickness of the IMCs increases with increasing temperature and holding time, the transition from Cu 3 Al 2 to Cu 9 Al 4 is also observed at 893 K. The activation energies of the Cu 3 Al, Cu 9 Al 4 and total IMCs layers are obtained from the Arrhenius equation and are 127.10 kJ/mol, 189.68 kJ/mol and 184.93 kJ/mol, respectively, which provide a reference for assessing the ease of growth of IMCs.

Modeling of Microstructural Evolution in Hard Turning of AISI-52100

White layers formed during machining of AISI-52100 decrease the fatigue life of dynamically loaded components. It is critical to predict the temperature and microstructure evolution of machined surfaces. This research examined 3D simulation of hard turning using a round insert. Voce-Johnson Cook constitutive law and hardness-based microstructural evolution model were incorporated. To reduce the excessive computational time, the 3D simulation was simplified to a 2D simulation. The predicted cutting forces, temperature, and microstructure changes were validated against experimental data. The results showed the accuracy of the process simulation for process optimization in order to avoid white layer formation.

Analysis of the Microstructure Development of Nb-Microalloyed Steel during Rolling on a Heavy-Section Mill.

It is not realistic to optimize the roll pass design of profile rolling mills, which typically roll hundreds of profiles, using physical modelling or operational rolling. The use of reliable models of microstructure evolution is preferable here. Based on the mathematical equations describing the microstructure evolution during hot rolling, a modified microstructure evolution model was presented that better accounts for the influence of strain-induced precipitation (SIP) on the kinetics of static recrystallization. The time required for half of the structure to soften, t0.5, by static recrystallization was calculated separately for both situations in which strain-induced precipitation occurred or did not occur. On this basis, the resulting model was more sensitive to the description of grain coarsening in the high-rolling-temperature region, which is a consequence of the rapid progress of static recrystallization and the larger interpass times during rolling on cross-country and continuous mills. The modified model was verified using a plain strain compression test (PSCT) simulation of rolling a 100-mm-diameter round bar performed on the Hydrawedge II hot deformation simulator (HDS-20). Four variants of simulations were performed, differing in the rolling temperature in the last four passes. For comparison with the outputs of the modified model, an analysis of the austenite grain size after rolling was performed using optical metallography. For indirect comparison with the model outputs, the SIP initiation time was determined based on the NbX precipitate size distribution obtained by TEM. Using the PSCT and the outputs from the modified microstructure evolution model, it was found that during conventional rolling, strain-induced precipitation occurs after the last pass and thus does not affect the austenite grain size. By lowering the rolling temperature, it was possible to reduce the grain size by up to 56 μm, while increasing the mean flow stress by a maximum of 74%. The resulting grain size for all four modes was consistent with the operating results.