The Connection Between Microstructural Evolution and Metal Friction: Combining Experiments Simulations and Theory into a Predictive Model.
Abstract not provided.
Argibay, Nicolas↗
SEARCH · Engineering Papers
Results for “Microstructural evolution”
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Modelling of Microstructure Evolution in Wire-Based Laser Direct Energy Deposition with Ti-6Al-4V
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Lee, Yousub↗
Mesoscale modeling of Microstructural Evolution in High Burnup UO2 Fuel and Transient Response
Overview of work done to model UO2 HBS modeling at an upcoming DOE-CEA meeting.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
Evolution of Microstructure and Creep Behavior in an Fe-Ni-Cr-Nb-C Alloy during Service in Hydrocarbon Cracker Tubes
Heat resistant, cast austenitic Fe-Ni-Cr-Nb-C alloy tubes are used by the petrochemical industry to transport hydrocarbons at temperatures between 850 and 1050 °C. Exposure to carbon from the process stream and nitrogen from the air causes severe carburization and nitridation in the tube walls, which influences creep resistance and degrades their ductility. A better understanding of these processes would enable their service life to be extended. To this end, we report the results of an experimental and computational study of the changes in microstructure and creep behavior in a representative alloy during service. The microstructure of the fresh material is compared to that of 8- and 10-year-old tubes. The results confirm the presence of M{sub 23}C{sub 6}, M{sub 7}C{sub 3}, and M{sub 2}(CN) phases reported in prior studies, and also reveal the nucleation and growth of the carbo-nitride phase M{sub 6}(CN). We show that the spatial variations of carbide and nitride particle volume fractions in aged tubes can be predicted by a simple reaction–diffusion equation. In addition, the uniaxial compressive creep response of the fresh and aged tubes was obtained as functions of temperature and strain rate. The materials deform by power-law creep, with strain rate versus stress relation as ε-dot =Aσ{sup n}. Aging reduces the stress exponent from n = 8 in fresh tubes to n = 5 in aged tubes, and also reduces the pre-exponential coefficient A. Tests on model alloys with composition identical to that of the matrix combined with finite element simulations of creep in model microstructures reveal that Cr depletion is responsible for the change in stress exponent, while the change in A is caused by the increase in particle volume fraction. By combining the microstructure-scale simulations of creep with the predictions of the reaction–diffusion model of microstructure evolution, the creep behavior of tubes left in service beyond 10 years is estimated.
36 MATERIALS SCIENCE↗
A Stochastic Reduced-Order Model for Statistical Microstructure Descriptors Evolution
Integrated computational materials engineering (ICME) models have been a crucial building block for modern materials development, relieving heavy reliance on experiments and significantly accelerating the materials design process. However, ICME models are also computationally expensive, particularly with respect to time integration for dynamics, which hinders the ability to study statistical ensembles and thermodynamic properties of large systems for long time scales. To alleviate the computational bottleneck, we propose to model the evolution of statistical microstructure descriptors as a continuous-time stochastic process using a non-linear Langevin equation, where the probability density function (PDF) of the statistical microstructure descriptors, which are also the quantities of interests (QoIs), is modeled by the Fokker–Planck equation. In this work, we discuss how to calibrate the drift and diffusion terms of the Fokker–Planck equation from the theoretical and computational perspectives. The calibrated Fokker–Planck equation can be used as a stochastic reduced-order model to simulate the microstructure evolution of statistical microstructure descriptors PDF. Considering statistical microstructure descriptors in the microstructure evolution as QoIs, we demonstrate our proposed methodology in three integrated computational materials engineering (ICME) models: kinetic Monte Carlo, phase field, and molecular dynamics simulations.
97 MATHEMATICS AND COMPUTING↗
Evolution of the Microstructure and Hardness of Fe-8Cr-2.1Mo-Si-V Die Steel at Different Cooling Rates after Hot Deformation
In this study, the effect of microstructure evolution, especially that involving the proeutectoid carbides, on hardness distribution of ledeburite steel containing 8% chromium content was investigated at different cooling rates after hot deformation. The continuous cooling transformation was carried out using a fully automatic transformation measuring apparatus under cooling rates in the range of 0.03-80 °C/s. The transformation temperatures, Ac1, Ac3 and Ms, were measured by dilatometry. A nanoindentation test was employed to evaluate the mechanical properties of the cooled specimens. The evolution of microstructure indicated that the proportion trend of the precipitated carbides was dependent on the cooling rates. In addition, a mixture of pearlite and proeutectoid carbides was observed under slow cooling rates in the range of 0.03-0.2 °C/s, for which only a martensite transformation took place in austenite, and the proeutectoid carbides precipitated negligibly at cooling rates greater than or equal to 10 °C/s. The results also showed that the nanohardness significantly decreased and then slowly increased to a stable value with increasing cooling rates, which was similar to the content trend of the carbides that precipitated during the cooling process.
36 MATERIALS SCIENCE↗
Effect of pre-cold rolling on the evolution of microstructure, microtexture, and mechanical properties of the mushy state rolled in-situ Al-4.5Cu-5TiB2 composite
Highlights: • Microstructure-Microtexture evolution study of the mushy state rolled composite (MRC) and MRC with pre-cold rolling (PCMRC). • The Microstructure and microtexture were characterized using SEM, EBSD, and TEM. • Exactly opposite trends in micro-hardness variation across the thickness of MRC and PCMRC were discussed. • The PCMRC exhibited the best combination of hardness, strength, and ductility. • A proper microstructure-microtexture-property correlation was established with experimental evidence. The mushy state rolling has been found as a promising technique for near-net forming of the cast Al-4.5 wt% Cu-5 wt% TiB{sub 2} in-situ composite to obtain microstructural refinement and moderate mechanical properties. Cold rolling with 30% reduction in thickness was carried out before mushy state rolling, for achieving a relatively more homogeneous distribution of CuAl{sub 2}-TiB{sub 2} particles as well as an appropriate microstructure to enhance the mechanical properties. A comparative investigation on the microstructural and microtextural evolution, along with mechanical properties of both the mushy state rolled composite (MRC) and pre-cold rolled mushy-state rolled composite (PCMRC) was performed, and the microstructure-property correlation was established. The PCMRC exhibited the lowest homogenized lengthscale parameter (L{sub H} 29 μm) indicating the maximum uniformity of particle distribution, computed with the help of multi-scalar analysis of area fractions (MSAAF) technique. Electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) studies revealed the presence of fine sub-grains within centrally located deformed Al grains due to dynamic recovery, as well as the particle stimulated nucleation of equiaxed fine Al grains by dynamic recrystallization or rapid solidification of liquid near edges for both the investigated composites. The PCMRC displayed a superior combination of hardness (96.82 ± 4.5 HV{sub 5kgf}), 40% higher ultimate tensile strength (301.4 ± 1.8 MPa), and 68% more uniform elongation (30.8% ± 0.5%), compared to the MRC. The improvement in mechanical properties is attributed to the uniform particle distribution and presence of both higher density of low angle boundaries and recrystallized grains adjacent to the particles, obtained from prior cold rolling.
36 MATERIALS SCIENCE↗
Part-scale evolution of fine-scale microstructural heterogeneity in solid-state additive manufacturing
Current solid-state additive manufacturing methods, refined through costly and time-consuming trial and error, have spurred interest in computational models that replicate material behavior under typical thermomechanical conditions (e.g., strain-rate ~ 102 s−1). These models, however, struggle to capture time-dependent microstructural evolution. In this work, Additive Friction-Stir Deposition (AFSD) is used as a representative case study for part-scale quantification of microstructure evolution at a fine spatial resolution (200 μm) by examining a liquid-nitrogen-cooled stop-action build via energy-dispersive X-ray diffraction coupled with a multi-channel detector. These results inform modeling efforts by linking process asymmetry to stored plastic strain, residual elastic strain, and texture development, and unlike current state-of-the-art characterization methods (e.g., EBSD or neutron diffraction), this approach provides both the spatial resolution and collection efficiency necessary to quantify fine-scale microstructural heterogeneity over large component volumes. As such, this technique provides essential validation data for computational models, e.g., crystal plasticity, enabling future prediction of heterogeneous behavior in AFSD and other additive manufacturing processes.
Franz, Cole [ORNL] (ORCID:0000000213465881)↗
A New Method for Optimizing Hot Processing Parameters of Mg-6.0Zn-0.5Mn-0.5Er Alloy Based on Kinetic Model of Dynamic Recrystallization and Processing Map
Hot deformation behavior of the cast-homogenized Mg-6.0Zn-0.5Mn-0.5Er alloy was studied using dynamic recrystallization (DRX) kinetic model and processing map. The compressing tests were conducted in the temperature range of 250-450 °C and strain rates of 0.001-1 s{sup −1}. According to the evolution of microstructures, under lower strain rates, the main DRX mechanism of Mg-6.0Zn-0.5Mn-0.5Er alloy is continuous DRX (CDRX); twinning induced DRX (TDRX) and CDRX both become the main DRX mechanism under higher strain rates. The DRX kinetics model of Mg-6.0Zn-0.5Mn-0.5Er alloy is calculated as X{sub DRX}=1−exp[−1.9463(((ε−ε{sub c})/(ε{sup ∗}))){sup 1.4608}], which is corresponding to the microstructure evolutions of DRX under different deformation conditions. The contour map of DRX was proposed based on the calculation results of DRX kinetics model. The processing maps are constructed to predict processing parameters of the alloy, and the predictability was evaluated combining with the contour map of DRX and dynamic materials model (DMM) processing map. It is deduced from the microstructures evolution and processing map that the optimum processing domain is mainly at 380-450 °C and 0.01-0.001 s{sup −1}, and 410-420 °C and 0.01-1 s{sup −1}.
36 MATERIALS SCIENCE↗
In-situ Experiments to Capture the Evolution of Microstructure During Phase Transformation of Titanium Under Dynamic Loading
Under sufficient stresses, such as during dynamic loading, titanium experiences a phase transformation from hcp alpha phase to hexagonal omega phase. Omega phase is often retained in the microstructure after unloading, and has a strong influence on subsequent mechanical properties. Simulations suggest there are multiple pathways and underlying mechanisms for this transformation. Due to the incredibly short timescales involved, experimental measurements for model validation have been difficult. However, new capabilities at the Advanced Photon Source have enabled diffraction measurements during plate impact experiments to study the evolution of titanium during transformation. These high-rate data allow us to probe the mechanism and kinetics of phase transformations in new ways. Recent results will be presented and compared to post-mortem characterization of soft-recovered shocked specimens. Comparisons are then made with previous tests where material was shock-loaded and soft recovered for microstructural analysis. Together these techniques create a consistent picture of material behavior during the shock-induced α–ω phase transformation in titanium.
36 MATERIALS SCIENCE↗
Additive manufacturing of metal matrix composites
Although Metal matrix composites (MMCs) are superior to most sought-after metallic alloys, their challenging fabricability has limited their widespread use in bulk-form applications. Among the many advanced fabrication techniques, Additive Manufacturing (AM), owing to its unique capabilities to produce near-net shapes, has drawn significant traction in the past two decades, especially for materials that are difficult to process using traditional methods. However, unlike pure metal/alloy systems, MMCs are highly sensitive to the processing conditions prevailing in AM techniques due to factors such as the high melting point of reinforcement particles and the potential for in-situ reactions. Therefore, it may be a while before metal matrix composites are commercially produced via AM. This review will discuss the current state-of-the-art design, fabricability, and performance of various additively manufactured MMCs. A particular focus will be on microstructural evolution and microstructure-property relationships. The most employed AM techniques, such as directed energy deposition, powder bed fusion, binder jetting, sheet lamination, and solid-state friction stir processing, are fundamentally different in terms of thermo-kinetics, forming the perspective for this review. A detailed comparison of microstructural evolution and process parameter optimization, including feedstock preparation methods and the role of machine learning and modeling among the different AM processes, is also presented. Finally, a critical evaluation of emerging AM technologies for MMCs is also provided, highlighting their potential advantages and challenges.
36 - MATERIALS SCIENCE↗
Rapid grain refinement and compositional homogenization in a cast binary Cu50Ni alloy achieved by friction stir processing
Friction stir processing (FSP) has been increasingly adopted for joining and processing materials in automotive, aerospace and industrial construction. During FSP a dynamic competition between high-speed shear deformation and deformation-induced heating brings about a complex competition between multiple dynamic microstructural evolution mechanisms making it difficult to predict the microstructural evolution pathway. Hence, improved understanding of microstructural evolution mechanisms during FSP can be beneficial for continued growth in the adoption of FSP for demanding applications of future. Towards this goal, this study uses a model binary Cu – 50 at.% Ni alloy to clarify the effect of single and double pass FSP on the microstructural evolution of a coarse grained and compositionally heterogeneous cast microstructure. High energy synchrotron X-ray diffraction, electron backscatter diffraction, and nanoindentation are used to clarify the microstructural evolution due to FSP. The process of compositional homogenization of as-cast segregations is studied by energy dispersive spectroscopy and atom probe tomography. Our results show that a single fast FSP pass at 30 mm.s -1 produces a 100 µm deep layer of submicrometric and hall-petch hardened CuNi grains. The initial cast compositional heterogeneities in a micrometric scale is rapidly transformed to nano-sized domains, mainly confined at grain boundaries. Double pass FSP increases the penetration depth of the processed layer and leads to a 2.9 times grain growth relative to single pass FSP. Grain fragmentation, discontinuous dynamic recrystallization, grain growth, and twinning mechanisms are discussed. In conclusion, these results highlight the value of FSP for ultrafast grain refinement and compositional homogenization of cast alloys.
36 MATERIALS SCIENCE↗
Evolution of microstructure and strength of a high entropy alloy undergoing the strain-induced martensitic transformation
In a recent work, we have reported outstanding strength and work hardening exhibited by a metastable high entropy alloy (HEA), Fe 42 Mn 28 Co 10 Cr 15 Si 5 (in at. %), undergoing the strain-induced martensitic transformation from metastable gamma austenite (γ) to stable epsilon martensite (ε). However, the alloy exhibited poor ductility, which was attributed to the presence of the brittle sigma (σ) phase in its microstructure. The present work reports the evolution of microstructure, strength, and ductility of a similar HEA, Fe 38.5 Mn 20 Co 20 Cr 15 Si 5 Cu 1.5 (in at. %), designed to suppress the formation of σ phase. A cast and then rolled plate of the alloy was processed into four conditions by annealing for 10 and 30 min at 1100 °C and by friction stir processing (FSP) at tool rotation rates of 150 and 400 revolutions per minute (RPM) to facilitate detailed examinations of variable initial grain structures. Neutron diffraction and electron microscopy were employed to characterize the microstructure and texture evolution. The initial materials had variable grain size but nearly 100% γ structure. Diffusionless strain induced γ→ε phase transformation took place under compression with higher rate initially and slower rate at the later stages of deformation, independent on the initial grain size. The transformation facilitated part of plastic strain accommodation and rapid strain hardening owing to a transformation-induced dynamic Hall-Petch-type barrier effect, increase in dislocation density, and texture. Here, the peak strength of nearly 2 GPa was achieved under compression using the structure created by double pass FSP (150 RPM followed by 150 RPM). Remarkably, the tensile elongation exhibited by the alloy was nearly 20% with fracture surfaces featuring a combination of ductile dimples and cleavage.
36 MATERIALS SCIENCE↗
On the evolution of microstructure and defect control in 316L SS components fabricated via directed energy deposition
To identify the critical issues that affect the evolution of microstructure during additive manufacturing, we investigated the influence of process parameters on the evolution of the dimensional and surface quality, microstructure, internal defects, and mechanical properties in 316L stainless steel (SS) components fabricated using laser engineered net shaping (LENS®), a directed energy deposition (DED) additive manufacturing (AM) technique. The results show that the accumulation of un-melted powder particles on the side walls of deposited sections can be avoided by selecting a laser under-focused condition. Moreover, we report that the variation of melt pool width is more sensitive to laser power than to the depth of the melt pool. The formation of a so-called “hierarchical” microstructure with cellular morphology is attributable to a combination of layer deposition and rapid solidification, which are characteristics of AM. Finally, we discuss microstructure evolution and defect formation, particularly the formation of multiple interfaces and the presence of un-melted powder particles and pores, in light of the dynamic convective fluid flow and rapid solidification that occur in the melt pool. X-ray computed tomography (X-CT) was used to precisely map the spatial distribution of pores in the DED components. The evolution of microstructure during DED is discussed in the context of related thermal phenomena in an effort to provide fundamental insight into the mechanisms that govern defect formation.
36 MATERIALS SCIENCE↗
A review: applications of the phase field method in predicting microstructure and property evolution of irradiated nuclear materials
Here, complex microstructure changes occur in nuclear fuel and structural materials due to the extreme environments of intense irradiation and high temperature. This paper evaluates the role of the phase field method in predicting the microstructure evolution of irradiated nuclear materials and the impact on their mechanical, thermal, and magnetic properties. The paper starts with an overview of the important physical mechanisms of defect evolution and the significant gaps in simulating microstructure evolution in irradiated nuclear materials. Then, the phase field method is introduced as a powerful and predictive tool and its applications to microstructure and property evolution in irradiated nuclear materials are reviewed. The review shows that (1) Phase field models can correctly describe important phenomena such as spatial-dependent generation, migration, and recombination of defects, radiation-induced dissolution, the Soret effect, strong interfacial energy anisotropy, and elastic interaction; (2) The phase field method can qualitatively and quantitatively simulate two-dimensional and three-dimensional microstructure evolution, including radiation-induced segregation, second phase nucleation, void migration, void and gas bubble superlattice formation, interstitial loop evolution, hydrate formation, and grain growth, and (3) The Phase field method correctly predicts the relationships between microstructures and properties. The final section is dedicated to a discussion of the strengths and limitations of the phase field method, as applied to irradiation effects in nuclear materials.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
Phase-field modeling of stored-energy-driven grain growth with intra-granular variation in dislocation density
Abstract We present a phase-field (PF) model to simulate the microstructure evolution occurring in polycrystalline materials with a variation in the intra-granular dislocation density. The model accounts for two mechanisms that lead to the grain boundary migration: the driving force due to capillarity and that due to the stored energy arising from a spatially varying dislocation density. In addition to the order parameters that distinguish regions occupied by different grains, we introduce dislocation density fields that describe spatial variation of the dislocation density. We assume that the dislocation density decays as a function of the distance the grain boundary has migrated. To demonstrate and parameterize the model, we simulate microstructure evolution in two dimensions, for which the initial microstructure is based on real-time experimental data. Additionally, we applied the model to study the effect of a cyclic heat treatment (CHT) on the microstructure evolution. Specifically, we simulated stored-energy-driven grain growth during three thermal cycles, as well as grain growth without stored energy that serves as a baseline for comparison. We showed that the microstructure evolution proceeded much faster when the stored energy was considered. A non-self-similar evolution was observed in this case, while a nearly self-similar evolution was found when the microstructure evolution is driven solely by capillarity. These results suggest a possible mechanism for the initiation of abnormal grain growth during CHT. Finally, we demonstrate an integrated experimental-computational workflow that utilizes the experimental measurements to inform the PF model and its parameterization, which provides a foundation for the development of future simulation tools capable of quantitative prediction of microstructure evolution during non-isothermal heat treatment.
Materials Science↗
Multi-scale modeling of the electric field assisted sintering process
The electric field assisted sintering (EFAS) process involves tightly coupled physics that influence microstructural evolution in the particles being compacted. It is also an inherently multi-scale phenomenon, with the microstructure of the compact influencing the subsequent engineering-scale response of the sintering system. To improve understanding of how processing parameters influence microstructural evolution, we have developed a multi-scale modeling approach that couples a continuum-level model of the sintering system with a phase-field model for microstructural evolution of particles within the compact. The phase-field model couples the effect of chemical and electrical driving forces on microstructural evolution and includes the effect of charged defect segregation to surfaces and grain boundaries; this segregation leads to enhanced defect transport and heat generation at these interfaces in response to applied electric field. The effect of enhanced heat generation on particle neck growth and the influence of microstructural evolution on the engineering-scale model are demonstrated.
36 MATERIALS SCIENCE↗