Microstructure Evolution Of Materials Research Articles

Extreme time extrapolation capabilities and thermodynamic consistency of physics-inspired neural networks for the 3D microstructure evolution of materials via Cahn–Hilliard flow

Abstract A Convolutional Recurrent Neural Network (CRNN) is trained to reproduce the evolution of the spinodal decomposition process in three dimensions as described by the Cahn–Hilliard equation. A specialized, physics-inspired architecture is proven to provide close accordance between the predicted evolutions and the ground truth ones obtained via conventional integration schemes. The method can accurately reproduce the evolution of microstructures not represented in the training set at a fraction of the computational costs. Extremely long-time extrapolation capabilities are achieved, up to reaching the theoretically expected equilibrium state of the system, consisting of a layered, phase-separated morphology, despite the training set containing only relatively-short, initial phases of the evolution. Quantitative accordance with the decay rate of the free energy is also demonstrated up to the late coarsening stages, proving that this class of machine learning approaches can become a new and powerful tool for the long timescale and high throughput simulation of materials, while retaining thermodynamic consistency and high-accuracy.

Thermal profile modeling and microstructural evolution in laser processing of Inconel 625 plates by comparison of analytical and numerical methods

Microstructural evolution of materials under specified process conditions and parameters can be predicted by thermal modeling of additive manufacturing laser processes. The objective of this study was to develop, analyze and compare two methods for prediction: an analytical method and a numerical method for laser processing of Inconel 625 material. These methods were compared with experimental results for thermal profiling, and the effect of thermal profiles on microstructure of the experimental samples was explored. Maximum temperature and cooling rate of the numerical method were shown in good agreement, while the analytical method proved more challenging when compared to the experimental results for three laser parameters. Cooling curves were correlated with microstructure in terms of grain size, morphology, and orientation, with findings trending with parameter adjustments. This research supports the numerical modeling approach as a method for examining optimal laser processing conditions for Inconel 625 that is ideally suited for complex fluid flow analyses.

Strengthening flat-die friction self-pierce riveting joints via manipulating stir zone geometry by tailored rivet structures

Achieving high-strength joints with flat surfaces is of significant importance for reducing wind resistance and enhancing aesthetic appeal. In this study, a novel flat-die friction self-piercing riveting (flat-die F-SPR) process is proposed. The rivet flaring without die guidance was achieved through the sophisticated design of rivet structures. Three types of rivets with different internal structures were designed to manipulate the base material flow and microstructure evolution during the joining process. Based on the method of emergency stop, the load-stroke curves, evolutions of macroscopic morphology, and microstructure of the joints made with different rivets were investigated. A novel mechanism for solid-state bonding of joints was proposed to elucidate the generation and evolution of fine grain regions. The results indicate when downward pressure is applied to the material inside the rivet cavity, a central stirring zone appears. By using a rivet with an annular boss structure, the base material flows continuously into the stirring zone and piled up in the rivet cavity, forming a unique conical-shaped fine grain zone. Finally, a comprehensive assessment of the strength of different types of joints and the transition of the fracture modes were conducted based on different lower sheet thicknesses. The joints of Rivet_B and Rivet_C demonstrate 11.1% and 6.9% strength enhancement compared with the joint of Rivet_A, respectively. Two strategies for enhancing the strength of solid-state bonding are proposed by analyzing the joint strengthening mechanism, which offers insights for the optimizations of rivet structures.

The influence of carbon content gradient and carbide precipitation on the microstructure evolution during carburizing-quenching-tempering of 20MnCr5 bevel gear

Due to the mechanism of microstructural transition, high-strength low-carbon alloy steel gears exhibit high strength and surface hardness after Carburizing-Quenching-Tempering (CQT) combined heat treatment, while maintaining good toughness in the core. The carbon potential gradient and the precipitation of carbides are the main factors affecting the final microstructure, yet there is a shortage of related research. To address this gap, this study developed a multi-physics coupled model considering the impact of carbon content to simulate microstructural transformation. Using finite element analysis, we simulated the microstructural evolution during the CQT heat treatment of 20MnCr5 bevel gear. By comparing the simulation results with the calculations from the commercial heat treatment software DANTE®, the accuracy of this model in predicting microstructural distribution and hardness has been validated. Furthermore, the study established a carbide precipitation kinetics model that takes into account the influence of grain size, to investigate the precipitation behavior of carbides within the matrix during the tempering stage. The cellular automaton method was applied to demonstrate the evolution process of the quenched microstructure during tempering. The study shows that during tempering, carbides primarily precipitate in areas with higher carbon content, preferentially at the boundaries of fine grains with a high density of lattice defects. As the carbon content increases, the number density of precipitates rises, while their average radius decreases. The reduction in matrix supersaturation due to carbide precipitation is one of the causes for the reduction of tooth surface hardness during tempering. The model constructed in this study provides a new perspective for understanding the laws governing material microstructural evolution and offers a solid theoretical foundation for the study of stress and deformation during the heat treatment process.

Microstructure evolution of cement-based materials under Cl−-SO42- coupling erosion in simulated ocean tidal area

To disclose the corrosion principle of cement-based materials used in ocean tidal surrounding, the effects of chloride ion (Cl−) and sulfate (SO42−) coupling erosion on the microstructure of cement-based materials were mainly investigated. In the presence of Cl− solution at a concentration of 0.6 mol/L, the phase composition, pore structure distribution, and microscopic morphology of the hardened slurry of composite cementitious material containing 30 % fly ash (FA), or 30 % ground granulated blast furnace slag (GGBS), or mixed with 15 % FA and 15 % GGBS with varying concentrations of SO42− were investigated, respectively. The impact of SO42− concentration and mineral admixtures on the chemical binding Cl− and microstructure was examined from the microscopic level. The results showed that adding GGBS or FA can resist Cl− and SO42− erosion; however, GGBS is more effective at chemically solidifying Cl− than that of FA. The erosion of Cl− and SO42− influence each other and contain each other. Furthermore, Friedel salt (FS) transforms into Ettringite (AFt) after the introduction of SO42−, which releases bonded Cl− into the pore solution thereby increasing free Cl− content. In higher concentration (0.8 mol/L) of Na2SO4 solutions, the cement-based material is subjected to the superimposed destruction of physical crystallization and chemical erosion of the salt solution.

Strain path dependent dynamic recrystallization and its resulted material flow and microstructure evolution of a titanium alloy

Changing strain path is an effective method to optimize the hot working process and improve microstructure and mechanical performance of titanium alloys. In this work, dynamic recrystallization (DRX) and its resulted material flow and microstructural behaviors in monotonic torsion (MT) and forward-reverse torsion (FRT) were comparatively explored by experimental and crystal plastic finite element simulation methods. The results indicate that both MT and FRT can induce discontinuous DRX (DDRX) and continuous DRX (CDRX). However, compared to MT where CDRX always prevails, FRT makes DDRX more important since it inhibits CDRX by recovering the lattice rotation during the reversal stage. Moreover, in FRT, the driving force and the grain boundary content for DDRX nucleation and bulging are relatively low at a small total strain. And the recovery of lattice rotation in FRT can also suppress CDRX. Therefore, DRX kinetics is obviously delayed at a smaller strain. As strain increases, both the stored energy for DDRX and the long-range misorientation gradient for CDRX are gradually greater, thus improve DRX kinetics. With these effects by DRX, although FRT exhibits a lower grain refinement degree at a smaller total strain compared to MT, it can make grain refinement degree rapidly rise and even close to that in MT at a greater strain. Also, FRT can obviously weaken the deformation texture by inducing extensive DDRX grains and recovering the lattice rotation of retained grains. In addition, the texture formed in forward stage and DRX delaying can result in a decrease in yield strength and softening rate in reversal stage, respectively, i.e., exhibiting remarkable Bauschinger effect, especially at a higher forward strain. These results can provide a basic guidance for designing the hot working process of titanium alloys to obtaining more refined microstructure and excellent properties of the components.

In-situ investigation of damage evolution and mechanism in composite propellants under monochromatic X-ray irradiation

Synchrotron radiation monochromatic X-ray computed tomography (CT) is a powerful tool for in-situ characterization of the internal microstructure evolution in composite materials. However, prolonged X-ray irradiation during long-term in-situ studies may affect the structure and properties of material. While the effects of white beam irradiation have been widely investigated, the specific damage mechanisms and material sensitivity to monochromatic X-ray irradiation, particularly in composite materials like propellants, are not well understood. In this study, we identify the threshold irradiation time that triggers radiation damage in PBT propellant and observe the accumulation and worsening of damage over time, primarilyinitiated by ether bond cleavage, leading to radiation-induced decomposition and increased internal porosity. This resulted in a significant reduction in the mechanical strength of PBT propellant, particularly under prolonged exposure to synchrotron radiation. In contrast, the inert binder system HTPB propellant exhibited better radiation stability. Our study highlights the importance of considering both radiation-induced damage and material X-ray sensitivity when designing in-situ synchrotron radiation CT experiments for composite materials, and suggests that the development of dynamic experimental methods to further reduce the risk of radiation damage for high-reliability in-situ assessment of material properties, as well as the need for careful consideration of radiation effects in the design and safety evaluation of solid propellant systems working in extreme circumstance.

Microstructure and corrosion behaviour of metal copper parts formed by laser shock

The effects of laser shock forming (LSF) on material microstructure evolution and its electrochemical corrosion behaviour were investigated. Results show that high-density dislocations and stacking faults are formed on the laser-irradiated surface layer of parts. The laser-irradiated surface of the parts subjected to two-shot LSF exhibited better corrosion resistance, with a 2-fold decrease in the passive current density, 3.5-fold increase in the charge resistance, and ∼12-fold thicker passive film compared with the undeformed sheet. The formation of nano-grains, compressive residual stresses, and a dense Cu2O oxidation film during LSF contributed to the improved corrosion resistance of the LSF-fabricated copper parts.

Exploring large language models for microstructure evolution in materials

There is a significant potential for coding skills to transition fully to natural language in the future. In this context, large language models (LLMs) have shown impressive natural language processing abilities to generate sophisticated computer code for research tasks in various domains. We report the first study on the applicability of LLMs to perform computer experiments on microstructure pattern formation in model materials. In particular, we exploit LLM’s ability to generate code for solving various types of phase-field-based partial differential equations (PDEs) that integrate additional physics to model material microstructures. The results indicate that LLMs have a remarkable capacity to generate multi-physics code and can effectively deal with materials microstructure problems up to a certain complexity. However, for complex multi-physics coupled PDEs for which a detailed understanding of the problem is required, LLMs fail to perform the task efficiently, since much more detailed instructions with many iterations of the same query are required to generate the desired output. Nonetheless, at their current stage of development and potential future advancements, LLMs offer a promising outlook for accelerating materials education and research by supporting beginners and experts in their physics-based methodology. We hope this paper will spur further interest to leverage LLMs as a supporting tool in the integrated computational materials engineering (ICME) approach to materials modeling and design.

Effect of bismuth on the mechanical properties and microstructure evolution of iron matrix during drawing: a molecular dynamics study

This paper investigates the effects of bismuth nanoparticles on the mechanical properties and microstructure evolution of single-crystal iron matrix materials during the drawing process using molecular dynamics methods, and also explores the effects of different drawing speeds and loading methods on the drawing process. The results show that the incorporation of bismuth nanoparticles has a significant effect on the axial drawing force, dislocation, shear strain and crystal evolution during the drawing process. When the bismuth nanoparticles started to deform under the action of drawing force, the atomic shear strain and crystal evolution were concentrated around them, which hindered the generation of dislocations and led to the reduction of their axial drawing force. In addition, the degree of atomic shear strain and crystal evolution increases with the increase of drawing speed, leading to work hardening of the material, and thus increasing the axial drawing force. Finally, when the loading mode is positioned at the rear end, shear strain becomes more concentrated around the bismuth nanoparticles, hindering dislocation generation and increasing the material’s hardness and axial drawing force. This study is important for understanding the mechanism of bismuth nanoparticles on the iron matrix of single-crystal during the drawing process.

A real space convolution‐based approximate algorithm for phase field model involving elastic strain energy

AbstractPhase field models have been employed extensively in the study of microstructure evolution in materials. Elasticity plays an important role in solid‐state phase transformation processes, and it is usually introduced into phase field models in terms of the elastic strain energy by applying Khachaturyan–Shatalov microelasticity theory. Conventionally, this energy is derived in the reciprocal space and results in full‐space Fourier transformation in practice, which becomes bottle‐neck in large‐scale and massively‐parallel applications. In this article, we propose an error‐controlled approximation algorithm for scalable and efficient calculation of the elastic strain energy in phase field models. We first derive a real‐space convolutional representation of the elastic strain energy by representing the equilibrium displacements in the Khachaturyan–Shatalov microelasticity theory using Green's function. Then we propose an error‐controlled truncation criterion to approximate the corresponding terms in the phase field model. Finally, a carefully designed parallel algorithm is presented to carry out large‐scale simulations. The accuracy and efficiency of the proposed algorithm are demonstrated by real‐world large‐scale phase field simulations.

Crystal plasticity based constitutive model for deformation in metastable β titanium alloys

Due to attractive mechanical properties, metastable β titanium alloys have become very popular in many industries including aerospace, marine, biomedical, and many more. It is often the complex interplay among the different deformation mechanisms that produces many of the sought-after properties, such as enhanced ductility, super-elasticity, and shape memory effects. Stress induced martensitic transformation is an important deformation mechanism for these alloys. Understanding of it and the influence it has on the microstructural evolution of materials is of great importance. To this end we have developed a crystal plasticity based constitutive model which accounts for both martensitic phase transformation and slip based plasticity simultaneously in metastable β titanium alloys. We present a new formulation for the evolution of martensite transformation, based on physical principles and crystal plasticity theory. To understand and demonstrate this feature of the model, a parametric assessment of the newly developed constitutive model is conducted. This is followed by first of its kind analyses of stress induced martensitic transformation in metastable β titanium alloys. We firstly present validations against uniaxial loading experiments for different metastable β titanium alloys exhibiting stress induced martensite transformation. As part of this, single crystal simulations in metastable β titanium alloys are used for the first time to investigate the interaction of individual transformation systems during unconstrained transformation. This study shows good agreement between the experimental and simulated responses during all stages of deformation in which elastic, transformation and finally the slip stage are exhibited. Relatively ‘strong’ and ‘weak’ orientations for transformation are observed, consistent with experimental studies. The work done here demonstrates the ability of this crystal plasticity finite element method to capture physical mechanisms while bringing new insight about the interaction of different deformation mechanisms in metastable β titanium alloys.

Polyphthalonitrile as a novel precursor for carbon membranes: Tunable microstructure characteristics and gas permeation behavior

Carbon molecular sieve (CMS) membranes hold great promise for energy-efficient gas separation, contributing to mitigating greenhouse gas emissions. Exploring new types of microstructurally tunable polymeric precursors is critical for understanding the evolution of carbon microstructure arrangement and adjusting the gas permeation behavior of CMS membranes. As a precursor for CMS membranes, polyphthalonitrile (PPN) resin with both tunable intermolecular distance and π-π stacking arrangement is reported for the first time. We have demonstrated that the aforementioned two key features of the thermally crosslinked PPN network are beneficial to forming PPN-CMS membranes with enlarged intermolecular distance and small-sized, narrow-distributed ultramicropores (<7 Å), thereby improving gas permeability and ideal selectivity. This study provides new insights into the microstructure evolution of PPN-derived microporous carbon materials. Owing to its excellent thermal stability, tunable microstructure arrangement, and flexibility of chemical synthesis, PPN represents a promising class of polymeric precursor materials for fabricating CMS membranes.

Thermo-mechanical effects and microstructural evolution-coupled numerical simulation on the hot forming processes of superalloy turbine disk

Abstract Macroscopic deformation and microstructural evolution simultaneously exist in the hot forming processes of superalloy. In order to effectively and accurately study the hot forming processes of superalloy turbine disk with the numerical simulation method, a multi-scale finite element model of GH4065 superalloy turbine disk involving macroscopic and microscopic aspects was established by defining macro- and micromaterial model of superalloy, hot forming processing parameters, and boundary conditions. Via the numerical simulations of superalloy turbine disk, the macroscopic material flow and microstructural evolution behaviors in the hot forming processes of superalloy turbine disk were studied. Besides, the macroscopic deformation and microstructure distribution states after the hot forming processes were revealed and analyzed. A corresponding hot forming physical test of superalloy turbine disk was conducted to verify the results of the numerical simulation. Via the qualitative and quantitative analyses, it was concluded that the macroscopic deformation and microstructural evolution in the hot forming processes of superalloy turbine disk can be accurately predicted by the numerical simulation method.

Understanding the microstructure evolution of carbon-doped Sb2Te3 phase change material for high thermal stability memory application

The Sb2Te3 phase change material shows a growth-dominated crystallization mechanism with fast phase transition but poor thermal stability of the amorphous state. This work investigated the effects of carbon doping on the thermal stability, microstructure, and electrical properties of the Sb2Te3 material. The 10-year data retention temperature of the material increased to ∼147.3 °C and the size of the grains was limited to ∼10 nm by carbon doping. The formation of the C cluster upon crystallization was found at the grain boundaries, which was accelerated as the temperature increased due to the break of the Sb–C bonds. The memory device based on the carbon-doped Sb2Te3 material exhibited a switching speed of 15 ns and an endurance of ∼105 cycles with a resistance ratio of more than two orders of magnitude. This work suggests that the carbon-doped Sb2Te3 material is a promising candidate for memory applications that require high thermal stability, fast speed, and high endurance.

Effect of hydrogen, helium and dose rate on the evolution of dislocation loop in pure iron during in-situ ion irradiation

Simulating neutron irradiation with ion irradiation requires considering the comprehensive effects of hydrogen, helium and dose rate to fully understand the microstructure evolution of material in an irradiation environment. Here, the characterization and evolution of dislocation loops in pure iron were investigated under heavy ion irradiation with four different injected gas ion types (Fe+, Fe++H2+, Fe++He+and Fe++H2++He+) and under dual-beam (Fe++He+) irradiation with four different dose rates using in-situ transmission electron microscopy at 723 K. Comparing to the single-beam (Fe+) irradiation, the additional injection of H or He, or co-injected H and He, mainly promoted the nucleation of dislocation loops at the early stage of irradiation and enhanced loop growth after that. Among them, the simultaneous irradiation of triple beams (Fe++H2++He+) was most pronounced. Moreover, triple-beam (Fe++H2++He+) irradiation resulted in the highest ratio of the rotation of loop habit-plane. Under dual-beam (Fe++He+) irradiation, the results demonstrated that as the dose rate increased, the loop density increased and the loop size decreased. Moreover, the fraction of 〈100〉 loops at low dose rate was noticeably greater than that at high dose rate. The results of the current work provide important references for a better understanding of the effectiveness of ion irradiation in simulating neutron irradiation.

A hardness-based constitutive model for numerical simulation of blind rivet with gradient hardness distribution

A286 superalloy blind rivets find extensive applications in the structural connections of aerospace equipment owing to their exceptional strength and heat resistance. However, the gradient hardness distribution within the rivet sleeves complicates achieving precise numerical simulation results with traditional constitutive models. This study aims to establish a constitutive model suitable for materials exhibiting gradient hardness to support the development of A286 superalloy blind rivets. Initially, quasi-static compression experiments were conducted on A286 superalloy samples at different hardness levels (160–324 HV), strain rates (0.01–10 s⁻¹), and temperatures (25–600°C). Subsequently, the influence of material microstructural evolution on flow stress during compression was investigated using electron backscatter diffraction technique. Furthermore, a hardness-based Johnson-Cook (J-C) constitutive model was developed by introducing hardness and offset compensation onto the original J-C model and compared with its counterpart. Finally, the hardness-based model was employed to simulate the bulge compression forming of A286 blind rivets and validated through experimental trials. The findings reveal that dislocation strengthening predominantly contributes to the increased material flow stress with escalating strain rates and sample hardness. Compared to the original J-C model, the stress prediction error of the hardness-based model reduced from 26.8 % to 2.9 %, effectively depicting the variation in material flow stress under different hardness values. The simulated values of bulge morphology, dimensions, and load closely align with experimental data, affirming the efficacy of the hardness-based model in numerically simulating blind rivets with gradient hardness distribution.

Microstructural Evolution and Failure in Fibrous Network Materials: Failure Mode Transition from the Competition between Bond and Fiber.

For the complex structure of fibrous network materials, it is a challenge to analyze the network strength and deformation mechanism. Here, we identify a failure mode transition within the network material comprising brittle fibers and bonds, which is related to the strength ratio of the bond to the fiber. A failure criterion for this type of fibrous network is proposed to quantitatively characterize this transition between bond damage and fiber damage. Additionally, tensile experiments on carbon and ceramic fibrous network materials were conducted, and the experimental results show that the failure modes of these network materials satisfy the theoretical prediction. The relationship between the failure mode, the relative density of network and strength of the components is established based on finite element analysis of the 3D network model. The failure mode transforms from bond damage to fiber damage as increasing of bond strength. According to the transition of the failure modes in the brittle fibrous network, it is possible to tailor the mechanical properties of fibrous network material by balancing the competition between bond and fiber properties, which is significant for optimizing material design and engineering applications.

A thermal damage-coupled constitutive model for predicting fracture and microstructure evolution and its application in the hot spinnability process

Although different damage-coupled physically based models have been proposed, those damage models are established based on the isothermal uniaxial or multi-axial tensile condition. However, the influence of the stress state on ductile failure strain is not adequately considered in the thermal damage models. It is widely recognized that the stress state has significant effect on damage evolution and ductility fracture for metallic materials. Actually, the current damage-coupled physically based models are not suitable for complex hot forming and the applications of these damage-coupled models are mainly focused on sheet hot stamping forming to date. Therefore, a modified damage-coupled unified model considering a broad range of stress states was established to figure out the complex damage behavior and microstructure evolution of metallic materials during the thermal deformation process. In this study, the Mg-6Gd-5Y-0.3Zr alloy was used as the experimental material. First, the flow behavior of the alloy was explored using a series of experiments under various stress states (i.e., uniaxial tensile, shear and compression) under various combinations of strain rates and temperatures. On this basis, a modified damage-coupled physics-based model was developed, in which the dynamic recrystallization, damage, stress triaxiality and Lode parameter were included as internal state variables. Furthermore, the model was integrated into ABAQUS to verify the applicability using hot spinnability test because the stress state was very complex during the forming process. The comparison between the calculated results and experiments is carried out. According to the simulation result, the predicted ultimate thinning rate is 71.14%, with an error of only 7.85% from the experimentally measured ultimate thinning rate of 77.2%, and the correlation coefficient and error for thickness and profile between the predicted values and experimental values are 0.9980 and 5.05%, respectively. These demonstrate that the developed model is reliable.

Tuning heterogeneous geometric microstructure of Cu-based materials via powder metallurgy for improving high synergistic strengthening and electrical conductivity

Designing heterogeneous structures (HS) is recognized as a promising method to achieve high performance for Cu-based materials. However, how to tune and control stably still remains challenging. In this work, a reproducible method based on powder metallurgy and heat treatment is proposed for designing controllable HS. Herein, spatial distribution of coarse and fine grains can be controlled via addition of different volume fraction of Cu powder. The microstructure evolution of the resultant HSed material was characterized in detail by utilizing electron backscattered diffraction (EBSD) combined with a transmission electron microscope (TEM). An optimal heterogeneous geometric microstructure consisting of individual isolated micron-sized grain completely surrounded and constrained by the hard ultrafine-grained Cu-Cr0.67 matrix is discovered, which produced an excellent combination of high yield strength (531.4 ± 10.3 MPa), uniform elongation (～22.1%)，and conductivity (～90.4% IACS) (International Annealed Copper Standard). The well-dispersed and high-density soft/hard zone interfaces in the resultant HS cause geometrically necessary dislocations (GNDs) piling ups, which produce extra strain hardening to enhance the strength and ductility. This reproducible method provides a feasible strategy to optimize the mechanical properties of metals via tailoring HS.