Modeling Of Microstructure Evolution Research Articles

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.

Dislocation density and twinning-related constitutive modeling of substructural evolution in Sn-5Sb-0.5(Ag/Cu) alloys under monotonic deformation

The development of a numerical model and experimental evaluation of microstructural evolution during the deformation of such materials are of pronounced significance. In the current work, evolutions of the substructure in three Sn alloys, namely Sn-5Sb, Sn-5Sb-0.5Ag, and Sn-5Sb-0.5Cu, were investigated using a dislocation density constitutive equation. The mechanical behavior of such alloys has been assessed, taking advantage of Ag and Cu addition and substructure-based factors like dislocation density, size, and misorientation. A comprehensive constitutive equation was developed for modeling the flow behavior of Sn-based alloy through the substructure-based tensile response of the material. It has been perceived that Cu is more in effect to improve the strength of Sn than Ag and Sn-5Sb-0.5Cu alloy is with enhanced work hardening rate during the tensile state of deformation. Dislocation density formulation results have direct implications on the capability to explicitly model the superimposed effect of dislocation densities and subgrain boundaries on the macroscopic mechanical properties of polycrystals. A numerical description of twinning stress in studied BCT alloys is described by the dislocation production kinetic model considering dislocation pile-up as the dominant mechanism. The developed slip-twinning transition model is incorporated into the deformation maps to identify the twinning domain.

Quasi in-situ observations of microstructure evolution during low cycle fatigue in carbide-free bainitic steel

Microstructure evolution during fatigue is crucial to the initiation and propagation of fatigue cracks in carbide-free bainitic steels. Utilizing quasi in-situ electron back-scattered diffraction method, the morphology of retained austenite and the accumulated plastic deformation within the bainitic laths at different fatigue stages were characterized. The observations disclosed that the retained austenite in various locations has different mechanical stability, and the dislocations in the bainitic laths will evolve to low-energy substructures continually throughout the fatigue process. Furthermore, combined with hysteresis curves analysis, a microstructural evolution model that comprehensively considered the retained austenite stability and the evolution of dislocations was proposed.

Modeling of dendritic solidification and numerical analysis of the phase-field approach to model complex morphologies in alloys

Dendrites are one of the most widely observed patterns in nature, and occur across a wide spectrum of physical phenomena—from snow flakes to river basins; from bacterial colonies to lungs and vascular systems; and in solidification and growth patterns in metals and crystals. The ubiquitous occurrence of these “tree-like” structures can be attributed to their excellent space-filling properties, and at times, dendritic structures also spatially manifest fractal-like distributions. As is the case with many fractal-like geometries, the complex multi-level branching structures in dendrites pose a modeling challenge, and a full resolution of dendritic structures is computationally very demanding. In the literature, extensive theoretical models of dendritic formation and evolution, essentially as extensions of the classical moving boundary Stefan problem exist. Much of this understanding is from the analysis of dendrites occurring during the solidification of metallic alloys, as this is critical for understanding microstructure evolution during metal manufacturing processes that involve solidification of a liquid melt. Motivated by the problem of modeling microstructure evolution from liquid melts of pure metals and metallic alloys during metal additive manufacturing, we developed a comprehensive numerical framework for modeling a large variety of dendritic structures that are relevant to metal solidification. In this work, we present a numerical framework encompassing the modeling of Stefan problem formulations relevant to dendritic evolution using a phase-field approach and a finite element method implementation. Using this framework, we model numerous complex dendritic morphologies that are physically relevant to the solidification of pure melts and binary alloys. The distinguishing aspects of this work are—a unified treatment of both pure metals and alloys; novel numerical error estimates of dendritic tip velocity; and the study of error convergence of the primal fields of temperature and the order parameter with respect to numerical discretization. To the best of our knowledge, this is a first of its kind study of numerical convergence of the phase-field equations of dendritic growth in a finite element method setting. Further, using this numerical framework, various types of physically relevant dendritic solidification patterns like single equiaxed, multi-equiaxed, single columnar and multi-columnar dendrites are modeled in two-dimensional and three-dimensional computational domains.

Design of spark plasma sintering parameters and preparation of Al2O3/TiB2/TiC micro–nano composite ceramic tool material

AbstractA microstructure evolution model for the ceramic materials was constructed, and the spark plasma sintering parameters were optimized using the model to shorten the designing period and reduce the consumption of the material. Based on the optimized sintering parameters, the ceramic tool material with a composition of Al2O3, TiB2, and TiC proved to be a success. It verified that the materials prepared under the optimized sintering parameters exhibited excellent mechanical properties. The results showed when sintered at 1600°C, under the pressure of 40 MPa and with the holding period of 7 min, the materials with 70% Al2O3, 20% TiB2, and 10% nano‐TiC possess the relatively best performance, with the hardness, fracture toughness, and flexure strength being 20.3 GPa, 10.5 MPa/m2, and 839.5 MPa, respectively.

Microstructure evolution and constitutive model for a Ni-Mo-Cr base alloy in double-stages hot compression with step-strain rates

The flow characteristics of a Ni-Mo-Cr base alloy are researched by the double-stages hot compression with step-strain rates. Electron backscatter diffraction (EBSD) as well as transmission electron microscopy (TEM) are adopted to systematically comprehend the influences of compressed parameters on microstructural changes. To forecast the hot compressed behaviors, a physically-based constitutive model with considering the evolution characteristics of dislocation density, subgrain and the grain structure is developed. Experimental results indicate that the elevated compressed temperature can exacerbate the dislocation consumption, subgrain rotation/interaction and dynamic recrystallization (DRX) grains coarsening. However, the prominent dislocation accumulation, subgrain generation and the refinement of DRX grains come up as the strain rates at the first or second stage of hot compression are ascended. The discontinuous DRX characterized by the bulging/serrated of grain boundaries is the major DRX nucleation mechanism of the researched alloy. The forecasted compressed stress, grain size and DRX fraction well match the tested results, which indicates the constructed physically-based constitutive equations can be employed to model the high-temperature features and microstructural changes of the studied Ni-Mo-Cr base alloy in double-stages hot compression with step-strain rates.

Simulation study on the effect of grinding temperature and cooling rate on microstructure evolution of 9310 steel grinding surface

The microstructure change of the workpiece surface during the grinding process will directly affect its mechanical property. Therefore, simulating the microstructure evolution process of the machined surface during the grinding process by establishing a mathematical model and obtain the influence of grinding temperature and cooling rate on grinding surface microstructure evolution, it is of great significance to guide the grinding process to obtain better machining quality. This paper defined the cellular automata rules for the nucleation and growth of lath martensitic, and established the microstructure evolution model during surface grinding of 9310 steel. By comparing the microstructure of the grinding surface obtained from simulation and experiment, it is found that the lath martensite is formed in the austenite in both of them, and the average grain size obtained from both of them is similar. Through the simulation analysis of the influence of different maximum grinding temperatures and cooling rates on the grinding surface microstructure evolution of 9310 steel, it is found that the smaller martensite microstructure can be obtained by decreasing the grinding temperature and increasing the cooling rate, thus the grinding surface has higher hardness and better wear resistance.

Physics-of-degradation-based life prediction of solder interconnects of long-life solar arrays in low-earth orbit

Exact prediction of lifespans of solder interconnects is critical for designing reliable solar photovoltaic systems that operate for a long time across a wide range of temperatures in low earth orbit, but pertinent prediction methodology has rarely been investigated. Here, a systematic approach for analyzing the fatigue life of the solder interconnects was developed concurrently using experimental, computational, and analytical methods. Physics of failure was examined using thermal cycling, thermal aging, and materials characterization. Solder interconnect geometry as well as strain distribution and evolution were determined through equilibrium liquid surface simulation and finite element simulation. Microstructure evolution modeling, constitutive equation fitting, and fatigue model calibration were conducted to reliably predict solder interconnect lifetime. Using this integrated approach to busbar-to-wire solder interconnects in photovoltaic systems, we have demonstrated that increasing the stand-off height of solder interconnects can delay the onset of the fatigue cracks and prolong the total fatigue life. The interconnects with large solder amount go through long life due to slow crack propagation with low averaged plastic work, but they possess nearly the same number of cycles to fatigue crack initiation because of relatively fixed plastic strain range under thermal cycling. The approach proposed would be useful to inspire the design of robust interconnects in photovoltaic systems that survive harsh thermal cycling (−90 to + 130 °C).

A Unified Constitutive Model for CLAM Steel Coupling Microstructure Evolution and Considering Phase Transformation in a Wide Range of Temperatures

A Unified Constitutive Model for CLAM Steel Coupling Microstructure Evolution and Considering Phase Transformation in a Wide Range of Temperatures

Frictionless Motion of Diffuse Interfaces by Sharp Phase-Field Modeling

Diffuse interface descriptions offer many advantages for the modeling of microstructure evolution. However, the numerical representation of moving diffuse interfaces on discrete numerical grids involves spurious grid friction, which limits the overall performance of the model in many respects. Interestingly, this intricate and detrimental effect can be overcome in finite difference (FD) and fast Fourier transformation (FFT)-based implementations by employing the so-called sharp phase-field method (SPFM). The key idea is to restore the discretization-induced broken translational invariance (TI) in the discrete phase-field equation by using analytic properties of the equilibrium interface profile. We prove that this method can indeed eliminate spurious grid friction in the three-dimensional space. Focusing on homogeneous driving forces, we quantitatively evaluate the impact of spurious grid friction on the overall operational performance of different phase-field models. We show that the SPFM provides superior degrees of interface isotropy with respect to energy and kinetics. The latter property enables the frictionless motion of arbitrarily oriented diffuse interfaces on a fixed 3D grid.

Experimental characterization and physical modeling of strain path dependent microstructure evolution: A case study of primary hot working of titanium alloy

Lamellar globularization, a multi-stage and significant microstructure transformation behavior during primary hot working of titanium alloys, directly affects the microstructure and performance of the product. However, the lamellae dynamic globularization represents a significant dependence on the strain path, which is hard to be predicted only by experimental characterization. To deepen the scientific insight into the effect of the strain path on the globularization behavior, systematic non-monotonic loading experiments (including multi-axial compression and forward-reverse torsion) were extensively performed to characterize the structure features. Further, an internal-state-variable microstructure model is developed to track the globularization process. Experimental results show that there is a short-term stage where the formed α/α substructures annihilate due to the restoration of ideal BOR during the early deformation after the loading direction changes, which leads to the reduction in globularized fraction. However, on the other hand, the globularization would be improved due to the adjustment in lamellae orientation and accelerated lamellae rotation caused by the change of loading direction. The microstructure model considering the strain path effect is developed by introducing the description of the strain path and coupling it into the physical model incorporating dislocation density and α/α substructures evolution. The proposed model is suitable for predicting the lamellar globularization under monotonic and non-monotonic loading of titanium alloys with the α-colony structure, which has been validated from the comparative analysis of the simulated and experimental results. Compared with the existing microstructure models, it broadens the scope of application and improves prediction efficiency. This work throws some light on the correlation between the strain path and microstructural development, which can be utilized to optimize the primary hot working of titanium alloy aiming at improving microstructural refinement and heterogeneity of forging pieces.

Strategy of refining the microstructure of Nd-Fe-Co-Ga-B ribbons by high-speed melt-spinning and annealing

• Increasing the melt-spinning speed to 50 m/s refines the grain size. • Changing the crystallization process is the mechanism of grain refinement. • The size of equiaxed grains in the annealed ribbons is reduced to 50–200 nm. • The intense exchange coupling effect contributes to the higher remanence. • The microstructure evolution models are proposed. Given the uneven grain size distribution in the ribbons melt-spun at 25 m/s, the strategy of improving the microstructure and magnetic properties of the ribbons by increasing the melt-spinning speed is discussed. The experimental results show that the grain size of Nd 13.65 Fe 73.55 B 5.6 Co 6.6 Ga 0.6 ribbons annealed at 700 °C is reduced to 50–200 nm by melt-spinning at 50 m/s. The change in the crystallization process is the primary mechanism for grain refinement. At high quenching speed, the amorphous matrix is formed first in the as-spun ribbons, and then uniform crystallization can be achieved through annealing. Compared to the annealed ribbons melt-spun at 25 m/s, the Mr and M 2T increased by ∼8 % due to the intense exchange coupling effect and the refined grains.

Thermomechanical processing model and abnormal microstructure evolution of high-nitrogen stainless steel X30CrMoN15-1

The high temperature deformation behavior of a X30CrMoN15-1 high-nitrogen stainless steel has been investigated using uniaxial compression test in the temperature range of 850–1250 ℃ and strain rate of 0.001–10 s−1. An Arrhenius-based hyperbolic sine equation was used to establish the flow stress constitutive model of the alloy at high temperatures, and the activation energy was 385.5 kJ/mol. Processing maps based on the dynamic material model were developed for true strains of 0.2, 0.4, 0.6 and 0.8. The domain of the safe region was in two parts: first, a strain rate range of 1–10 s−1 and temperature range of 1000–1100 ℃, and second, a strain rate range of 0.3–0.001 s−1 and temperature range of 1100–1250 ℃. The deformed microstructure at 1050 °C was characterized at different strain rates, strong< 100 >fiber textures parallel to the compression axis developed during high temperature deformation, and the strength gradually increased and became more concentrated with decreasing strain rate. The maximum dynamic recrystallization fraction and geometrically necessary dislocation densities were recorded at a medium strain rate (ε̇=0.1s−1), which was more conducive than a low strain rate to the continuous dynamic recrystallization process. Discontinuous and continuous dynamic recrystallization both contributed to the microstructural evolution of the columnar grains studied in this research, but discontinuous dynamic recrystallization was the dominant mechanism.

Modeling of Dynamic Recrystallization Evolution for Cr8 Alloy Steel and Its Application in FEM.

In the process of Cr8 roller production, the phenomenon of coarse grain size and uneven grain size often appears, which makes the mechanical properties of the material decrease sharply. Accurate dynamic recrystallization model is the basis for predicting the change of grain size during thermal processing, and is an important basis for refining grain and improving material properties. In this study, the isothermal compression experiment was carried out on Cr8 alloy steel at 900–1200 °C and 0.005–0.1 s−1 by Gleeble –1500D thermal simulation compressor, and the stress dates of Cr8 alloy steel were obtained. According to experimental data, the Kopp dynamic recrystallization model of Cr8 alloy steel was established. The dynamic recrystallization volume fraction obtained by Kopp model was compared with that obtained by experiment at the same temperature and strain rate. The correlation value was 0.988, and the root mean square error (RMSE) was 0.053, which proved that the DRX model established was reliable. Through the secondary development of the program, the DRX model of Cr8 alloy steel was written into the software Forge® to verify the microstructure evolution model. The compression process of a cylindrical specimen of Cr8 alloy steel at 0.1 s−1 and 1050 °C was simulated, and the DRX microstructure evolution of the alloy was calculated. The comparison between the final grain size calculation results and the test metallographic photos of samples in different deformation zones shows the relative error of the grain size was less than 10.6%, indicating that the DRX model of Cr8 alloy steel can better predict the dynamic recrystallization of Cr8 alloy steel.

Effect of doping Al-Cu-Fe alloy on the microstructure and magnetic properties of annealed Nd-Fe-Co-B ribbons

Doping 1 wt% Al89.5Cu9.7Fe0.8 alloy promotes the phase separation of Nd13.53Fe74.89Co5.54B6.04 alloy, forming the unique microstructure of small Nd-rich particles embedded in the large equiaxed Al-Cu-Fe-rich grains with the same Nd2Fe14B-type structure. Low-temperature annealing at 650 °C–710 °C improves the disorder degree of Nd2Fe14B-type phases and reduces the composition difference between different phases. Correspondingly, the large amorphous regions reduce to ∼20 nm small particles, and the small amorphous regions are crystallized into nanoclusters or nanoparticles. When the annealing temperature exceeds 750 °C, the grain composition is thoroughly homogenized, and the grains begin to overgrow. Al-Cu-Fe addition improves the thermal stability of some Fe-rich amorphous particles and makes them difficult to crystallize. Compared to the as-spun ribbons, annealing at 710 °C increased the coercivity by 72%, the remanence by 34%, and the maximum magnetization by 2.0%. At the same time, the corresponding microstructure evolution models are established.