Heterogeneous Microstructure Research Articles

Finite element based micromagnetic simulations of heterogeneous magnetic microstructures

AbstractMagnetic materials play a crucial role in our everyday lives. As permanent magnets, they are core components in electric motors such as generators for wind turbines, or, as magnetocaloric magnets, they have the potential to change the cooling technology of tomorrow. All of this makes these materials key contributors to “green” energy conversion technology. Accordingly, pushing the development of these materials with a special focus on the performance, efficiency, and harmlessness of the material components contained for humans and the environment is of crucial importance. This work deals with the finite element‐based simulations within the framework of the micromagnetic theory to numerically support the quest of characterizing novel magnetic materials. The main focus remains on the numerical modeling of permanent magnetic polycrystalline materials and the influence of grain boundaries on the effective magnetization. For this purpose, large‐scale simulations of permanent magnetic neodymium‐iron‐boron () samples are carried out and the influence of different mesh sizes on the effective magnetization behavior is investigated.

Unveiling the mechanical anisotropy and related deformation mechanisms of heterostructured Mg alloy laminate with unique texture feature

In this study, a well-bonded AZ31/ZK60/AZ31 sandwich-structured laminate was prepared using extrusion. Microstructural heterogeneities in grain size, precipitate phases, and texture were evident between the constituent layers. Tensile testing revealed significant mechanical anisotropy in the laminates along the extrusion direction (ED), transverse direction (TD), and 45° directions, with the 45° direction samples exhibiting the highest tensile ductility, while ED and TD samples showed similar high strength. In-situ electron backscatter diffraction and slip trace analysis indicated that the heterogeneities in grain size and precipitates had minimal influence on the mechanical anisotropy of the laminates. Instead, texture emerged as the primary influencing factor, as it affected the initiation difficulty of basal slip and extension twinning mechanisms in various directions, thereby influencing the deformation coordination between the successive layers and resulting in varied mechanical responses in different directions.

Mechanical Properties Optimization and Microstructure Analysis of Pure Copper Heterostructured Laminates via Rolling

Heterogeneous metallic structures constitute a novel class of materials with excellent mechanical properties. However, the existing process for obtaining heterostructures from a single material does not meet large-scale industrial requirements. In this study, a pure copper heterostructured laminate (HSL) composed of a surface elongated-grain layer and a central equiaxed-grain layer was fabricated by rolling bonding and annealing. To study the effect of the interface on the mechanical properties of gradient-structured materials, both laminate metal composite (LMC) and non-composite laminate (NCL) were fabricated by cold-rolling pretreatment of the center layer (60% reduction) and cold-rolling bonding of the whole blank (67% reduction). Then, the HSL was obtained by controlling the post-annealing regimes, the microstructure of each layer was optimized, and a larger degree of microstructural heterogeneities, such as grain size, misorientation angle, and grain orientation, was obtained, which resulted in obvious mechanical differences. Tensile tests of the HSL, surface layer, center layer, and NCL specimens revealed that the HSL annealed at 300 °C for 1 h had a significantly higher strength than the center layer and a higher elongation than the surface layer. The HSL had a tensile strength and elongation at fracture of 278.08 MPa and 46.2%, respectively, indicating a good balance of strength and plasticity. The improved properties were primarily attributed to the strengthening or strain hardening due to the inhomogeneous deformation of the heterogeneous layers in the laminate and the mutual constraint acquired by the distinct layers with strong mechanical differences. The HSL had an interfacial bonding strength of 178.5 MPa, which played a vital role in the coordinated deformation of the heterogeneous layers. This study proposes an HSL design method that effectively simplifies the process of obtaining heterostructures in homogeneous materials by controlling the cumulative deformation of the surface and center layers.

Enhancing strength-ductility synergy of Cu alloys with heterogeneous microstructure via rotary swaging and annealing

The trade-off of strength and ductility in the Cu alloys seriously restricts its wide application. In this study, the paradox of strength and ductility of the Cu alloy is ameliorated by rotary swaging (RS) and subsequent annealing, and reveals its microstructural evolution. It was found that the grain size was obviously refined after the RS, resulting in yield strength as high as 760 MPa but with a ductility of only 1.5 %. After annealing, the RS-350-20 sample (RS sample annealed at 350°C for 20 min) exhibited partial recrystallization at the edge and middle positions, while full recrystallization occurred at the center position, which formed a gradient grain size distribution. Tensile results showed that RS-350-20 sample exhibited an excellent combination of the yield strength of 495 MPa and ductility of 27%. High strength stemmed from residual deformation grains, recrystallized ultrafine/fine grains and heterogeneous deformation-induced (HDI) strengthening. The good ductility originated from recrystallized coarse grain, pronounced HDI hardening and activated deformation twins. In addition, microstructural characterization further revealed that dislocations were accumulated near the recrystallized grains to maintain strain continuity at the interface of deformed grains and recrystallized grains during tensile strain. With increasing strain, deformation twins were activated near the recrystallized grains, which facilitates high strain hardening capability meanwhile maintaining high strength. These findings provide insight for optimizing the strength and ductility of Cu alloys by a feasible processing.

Analysis of grain structure, precipitation and hardness heterogeneities, supported by a thermal model, for an aluminium alloy 7075 deposited by solid-state multi-layer friction surfacing

Thermomechanical cycles during multi-layer friction surfacing (MLFS) cause microstructural and mechanical heterogeneities in the deposited high-strength Al alloy, 7075. The thermal profile and heat accumulation were investigated in this study using a multilayer numerical thermal model of the MLFS process; additionally, these variables were linked to experimentally observed microstructural heterogeneities. Compared with the feedstock, grain sizes decreased by 55–80%. The mean grain size at the bottom and top areas of a given layer was finer than that in the middle of the layer because of the enhanced recrystallisation, which resulted from the friction and shear deformation experienced by the deposited material. The differences in the thermal cycle and plastic strain rate of the bottom and top areas along the layers resulted in a gradual increase in the grain size at the bottom of each layer and a reduction in the grain size at the top of each layer. The grain growth and continuous dynamic recrystallisation mechanisms are governed by the temperature and strain rate, those mechanisms determine the intra- and inter- layer grain sizes. The accumulated heat, owing to subsequent experimental deposition, resulted in excessive growth of the precipitates in the bottom layers. The strengthening of the solid-solution and Guinier-Preston zones significantly increased the microhardness of the top layer. Post-deposition T6 heat treatments confirmed the restoration of a uniform distribution of microhardness.

A novel age-hardenable austenitic stainless steel with superb printability

Precipitation-hardened high strength alloys, such as nickel-based alloys, aluminum alloys and stainless steels, are susceptible to hot cracking during 3D printing. This issue is typically mitigated by reducing solute segregation or promoting columnar-to-equiaxed transition. Here, we demonstrate an alternative approach by increasing segregation solutes, especially Ti element, to reduce hot cracking during laser powder bed fusion (L-PBF) additive manufacturing of a new austenitic stainless steel (ASS). Enhanced segregation triggers peritectic-like reactions at cell/grain boundaries, forming multiple phases that bridge FCC dendrites. As a result, the new ASS exhibited excellent printability across a broad range of processing parameters. The as-built (AB) steel displayed a heterogeneous columnar grain microstructure with fine L21/BCC/C14 precipitates partially decorating cell structures, achieving a yield strength (σ0.2) above 690 MPa and uniform elongation (εu) beyond 17.5%. The epitaxial growth of the columnar grains was frequently interrupted by puddles of fine grains, leading to near-isotropic tensile properties. Following isochronal annealing at temperatures between 600 to 1150 °C for two hours, the AB steel underwent varying degrees of microstructure evolution, resulting in a broad range of mechanical properties (σ0.2 from 300 to 1460 MPa and εu from 59.5% to 7.6%). This high strength is attributed to the formation of the L21/σ/η multiple phases at cell and grain boundaries, in combination with coherent L12-ordered (γ') nanoparticles precipitated within cell interiors during aging. This study explored that compositional design leveraging the unique solidification behavior of the L-PBF process can produce hierarchical-structured stainless steels with excellent printability and tunable mechanical performance.

Automated identification of soil functional components based on NanoSIMS data

NanoSIMS technique allows to investigate the micro-spatial organization in complex structures in multiple scientific fields such as material science, cosmochemistry, and biogeochemistry. In soil biogeochemistry applications, NanoSIMS-based approaches aim to disentangle the interactions of organic matter (OM) and mineral phases in the heterogeneous soil microstructure. Investigating the spatial arrangement of distinct organic and mineral functional components is necessary to understand how these components interact and contribute to biogeochemical processes in soil systems. Identifying soil functional components within NanoSIMS measurements necessitates advanced and efficient data processing tools capable of accessibility and automation. We have developed a pre-processing tool to streamline NanoSIMS data preparation and handling. The tool is provided as an open-source software toolbox (NanoT). In addition, a two-step unsupervised segmentation method was developed to identify soil functional components based on NanoSIMS analyses. To illustrate the segmentation method, here we describe its application to two exemplary NanoSIMS measurements. This allows to distinguish mineral- and OM-dominated regions, as well as different mineral phases. To improve the detection of iron oxides and aluminosilicates, the 56Fe16O− channel was separately processed. The presented NanoSIMS-based processing workflow helps to disentangle functional components within a biogeochemically-diverse microstructure in soils and further warrants applications to a wide range of complex environmental samples.

Microstructure and mechanical performances of NiCoFeAlTi high-entropy intermetallic reinforced CoCrFeMnNi high-entropy alloy composites manufactured by selective laser melting

Multi-component alloys have been confirmed to be excellent reinforcing phases in high-entropy alloy-based composite. However, achieving a balance between strength and ductility by controlling the reinforcement content remains a major challenge in the design of high-entropy alloy-based composites. In this study, CoCrFeMnNi HEA/NiCoFeAlTi HER high-entropy alloy composites were prepared using SLM technology. Interestingly, gas-atomized NiCoFeAlTi high-entropy intermetallic (HER) powder was selected as the reinforcing phase, and the CoCrFeMnNi HEA matrix was used for comparison. The influence of the reinforcement content on the composite was investigated, and high-performance HEA/HER composites were obtained, with the strengthening mechanism elucidated. The results showed that the composite with 1 wt.% HER reinforcement exhibited the optimal performance, with hardness, yield strength, ultimate tensile strength, and ductility at room temperature being approximately 226.9 HV, 562 MPa, 683 MPa, and 16%, respectively. The excellent mechanical properties at both room and elevated temperatures are attributed to the synergistic effects of heterogeneous microstructure strengthening, grain refinement, and precipitation strengthening. This work provides a foundation for the development of high-entropy alloy composites reinforced by high-entropy intermetallics.

Dynamic formation of gradient structure by microparticle impact — A crystal plasticity material point method study

Metallic materials with unique microstructure can achieve desirable strength-ductility synergy. However, effectively fabricating and precisely controlling microstructure distribution in metals remain challenging. Microparticle impact, the key process of cold spray technique, can lead to a gradient structure in the particle, which may also serve as a promising additive manufacturing technology. To investigate the dynamic formation mechanism of heterogeneous microstructure and its significant influencing factors, the crystal plasticity material point method (CPMPM) is developed, especially for microstructure formation under a high strain rate and large deformation. Our work provides a quantitative analysis of evolution of structural gradient during impact. It is found that decreasing grain size can afford a larger structural gradient and there is negligible influence on the compression ratio of particles. It suggests that microstructure distribution can be tailored by optimizing the impact process without influencing vertical deformation of particles.

Phase reversion mediated the dual heterogeneity of grain size and dislocation density in an equiatomic CrCoNi medium-entropy alloy

An ultra-high strain rate (104 s-1) dynamic plastic deformation treatment at liquid nitrogen temperature (LNT-DPD) followed by annealing is carried out to obtain dual heterogeneity of grain size and dislocation density in an equiatomic CrCoNi medium entropy alloy (MEA). Such extreme loading conditions resulted in extensive phase transformation in this MEA. Subsequent annealing at 650°C for 1 h further induced reverse phase transformation and partial recrystallization, forming a complex heterogeneous microstructure characterized by nested trimodal grain sizes and partitioned dislocation density. A superior yield strength of ∼800MPa and a good ductility of ∼40% were simultaneously achieved in this heterogeneous alloy. In order to reveal the effects of grain size and dislocation density distributions on the mechanical property improvements, the underlying deformation mechanisms were systematically discussed. High density of geometrically necessary dislocations (GNDs) would be induced in complex heterogeneous structures during tensile deformation due to strain gradients or partitioning between different regions, which would lead to additional strengthening and work hardening. These results provide a novel approach to overcome the strength-ductility trade-off dilemma for FCC-structured MEAs.

Heterogeneous dynamic restoration of Ti-15Mo alloy during hot compression

Near-β titanium alloys have shown low Young’s modulus and good strength, making them excellent implant candidates. However, their processing using thermomechanical routes in single phase β region results in heterogeneous microstructures due to high content alloying elements and consequent slow diffusion-controlled processes such as dynamic recovery. This study investigates the deformation behaviour of a Ti-15Mo alloy through hot compression experiments using a Gleeble ® 3800 device in the single β domain at strain rates from 0.01 s-1 to 10 s-1, reaching final strains of 0.50 and 0.85 followed by immediate water quench. The findings show that the material presents a low strain rate sensitivity. The flow curves show significant strain hardening before reaching a steady-state regime, particularly at high strain rates. The strain hardening exponent calculations support the effect of molybdenum on retarding softening mechanisms such as dynamic recovery. Electron backscatter diffraction (EBSD) measurements of deformed samples revealed that dynamic recovery is the primary restoration mechanism, with continuous and geometric dynamic recrystallisation evidence. Due to the slow restoration process, we observe the subgrain formation for different deformation parameters. Therefore, we introduced an EBSD-based method to quantify dynamic recovery and subgrain size. We concluded that for a given deformation, the areas of dynamically recovered and recrystallised regions decrease with increasing strain rate and decreasing temperature, exhibiting negligible variation at higher strain rates.

Ultra-strong cold-drawn 2507 stainless steel wire with heterogenous microstructure of dual-phase and grain size

Obtaining ultrafine grains through severe plastic deformation is a highly effective strategy for improving the strength of metallic materials. Due to the different deformation mechanisms between ferrite and austenite, the heavily drawn 2507 stainless steel wire possesses a significant heterogeneous structure at drawing strain ε = 6.65.In this study, a 2507 duplex stainless steel (DSS) with a strength of 2.7 GPa was prepared by cold drawing process. The deformation production of the ferrite in the wire is simply dislocation, which subsequently transforms to subgrain boundary and high angle grains boundary. While the production of the austenite is dislocation and twinning. In addition, based on the boundary strengthening, solid solution hardening and lattice friction, the contribution of the deformed ferrite and deformed austenite to the yield stress is 2260 MPa and 2800 MPa, respectively.

Microstructure Evolution and Wear Behavior of Stellite12 Coating Prepared by Laser-Directed Energy Deposition on H13 Steel

Laser-directed energy deposition (LDED) was employed to apply a Stellite12 coating onto an H13 steel substrate. This study explored the effects of processing parameters on the dimensions of the deposited tracks. Comprehensive examinations were conducted on the coatings to assess their phase composition, microstructure, and wear resistance properties. The relationship between microstructural characteristics and thermal field was investigated through a synergy of numerical simulations and experimental analyses. The findings revealed that the Stellite12 coating displayed a heterogeneous microstructure with epitaxial growth and a slight texture across successive layers. The primary phase comprised a γ-Co solid solution and M23C6 carbides, contributing to a significant enhancement in hardness, which was observed to be 2.2 times higher than that of the substrate. The coating demonstrated superior performance in terms of lower friction coefficients and reduced wear rates at both room and elevated temperatures. The predominant wear mechanisms identified were oxidative wear. These results underscore the promising applications of Stellite12 coatings in industrial contexts facilitated by LDED technology.

Microstructure-sensitive crystal plasticity and phase-field modeling of deformation and fracture in polycrystalline ice

The formation of crevasses in Greenland and Antarctica is primarily driven by the brittle failure of ice at low strain rates. Understanding this phenomenon requires exploring the effect of microstructural heterogeneity and anisotropic elastoplastic deformation on the fracture behavior of ice. Here, we have developed a microstructure-sensitive coupled crystal plasticity and phase-field model. This model allows us to study the plastic deformation, damage initiation and propagation under various strain rates in hexagonal open-packed polycrystalline ice, the prevailing phase on Earth. By employing a Bayesian optimization method, we derived the material parameters for the micromechanical model based on experimental results. The modeling results reveal that the activation of basal dislocations results in a brittle to ductile transition in ice at a low strain rate of 10-7s-1 under tension. At higher strain rates, the intrinsic plastic anisotropy of ice leads to heterogeneous deformation among grains and stress concentration near grain boundaries, triggering crack initiation and exacerbating the brittleness of ice. Under compression, cracks usually do not propagate throughout the specimen due to a significant decrease in stress around the crack tip upon propagation. Moreover, we found that the formation of the shear-induced basal texture at the bottom of ice layers and along glacier valley sides intensifies the brittleness of ice. This study provides insights into the micromechanical deformation and fracture mechanisms of ice, elucidating the intricate process of crevasse development in polar ice sheets.

ANXA2 Enhances the Malignancy of Gastric Cancer Cells by Remodeling Cytoskeleton

ANXA2 was reported as a multiple tumors relevant gene expressed excessively in many tumors, especially in cancers from the digestion system, and its aberrant expression enhances the malignant properties of cancer cells. We suppose that microstructure heterogeneity is important to maintain the malignancy of cancer cells, and ANXA2 excessive expression enhances the malignancy by remodeling the microstructures of cancer cells. To validate the proposal, we studied the effects of ANXA2 expression on the remodeling of motility-associated microstructures in SGC-7901 cells by a series of morphological display methods. The results showed that the cell motility microstructures, such as pseudopodia/filopodia and microvilli, were weaker and poorer in ANXA2-silenced SGC-7901 cells than in wild type cells, and the malignancy was significantly decreased in ANXA2 silenced SGC-7901 cells. These findings indicate that ANXA2 is necessary to maintain the changed cytoskeleton of cancer cells, especially the highly polymerized cytoskeleton protein, actin, and tubulin, which leads to the alteration of the cell microstructures that are closely correlated with cell motility. Our results indicate that ANXA2 plays an important role in enhancing the malignancy of gastric cancer cells by remodeling the cytoskeleton microstructures of polymerization. In this short article, we will try to shed light on this very important problem helping chronic pain patients to understand the nature of their pain and advising them how to deal with it.

Modulating NFO@N‐MWCNTs/CC Interfaces to Construct Multilevel Synergistic Sites (Ni/Fe‐O‐N‐C) for Multi‐Heavy Metal Ions Sensing

AbstractA hierarchical heterogeneous composite electrode of NiFe2O4@nitrogen‐doped multi‐walled carbon nanotubes/carbon cloth (NFO@N‐MWCNTs/CC) is prepared via a dip‐coating method, followed by a hydrothermal process. The flexible carbon cloth (CC) substrate provides robust support and the cross‐linked nitrogen‐doped multi‐walled carbon nanotubes (N‐MWCNTs) on the CC form a highly porous network with a large specific area that facilitates electron‐transfer. The stable support strengthens the framework and prevents pore structure disorder within the porous network, that could lead to the structural instability of the active sites. The decorated NiFe2O4 nanoparticles offer abundant active sites for enhanced electrocatalytic activity. Benefiting from the synergistic effect of the 3D hierarchical heterogeneous microstructure and multilevel bimetallic oxide active site (Ni/Fe‐O‐N‐C) constructs, the NFO@N‐MWCNTs/CC electrode achieves stable detection of multiple heavy metal ions (HMIs) with high reproducibility. The modified electrode allowed stable detection of multiple heavy metal ions with high reproducibility. The sensitivities of the electrode for Cd(II), Pb(II), Bi(III), and Hg(II) are 344.98, 441.02, 176.484, and 371.099 µA µm−1, respectively. The assay recoveries ranged from 95.3% to 106.8%, highlighting its practical applicability. This study provides innovative composites and theoretical insights to facilitate further advances in the simultaneous high‐performance detection of heavy metal ions.

Microstructure and mechanical properties of thin-walled TA1 titanium pipes fabricated by high-frequency induction welding

High frequency induction welding (HFIW) was effectively employed for the high-speed fabrication of thin-walled TA1 titanium pipes (TWTPs) with a nominal wall thickness of ∼0.6 mm. The microstructure and mechanical properties of TWTPs manufactured under varying welding parameters were investigated. The weld zone (WZ) exhibits a waist shape measuring ∼622 μm in width, and the width of the heat-affected zone (HAZ) spans between 763 and 864 μm. Both the WZ and HAZ are composed of a mixture of coarse serrated α grains with fine acicular and twins, while the BM retains equiaxed grains. This unique microstructure was resulted from the thermal cycling during HFIW, contributing to a notable increase in microhardness within the WZ compared to both the HAZ and the BM. Optimal manufacturing conditions were identified at a welding power of 14.4 kW, a welding speed of 60 m/min, an opening angle of 6°, and a squeeze displacement of 0.2 mm, yielding the TWIP with a tensile strength of ∼307 MPa and tensile elongation of ∼27%. Tensile fracture analysis revealed that failure predominantly occurred within the BM, underlining a ductile fracture mode characterized by pronounced dimple formations. The enhanced mechanical performance of the weld joints can be attributed to the heterogenous microstructure in the WZ, where the presence of large serrated α-grains enhances ductility, and the fine martensite and twins contribute to the high strength.

Synergetic effect of in-situ TiB2 reinforcement and nano precipitation on wear behavior of ZE41 magnesium matrix composite

The rise in carbon dioxide pollution and energy consumption has increased the demand for lightweight materials such as magnesium in automotive and aerospace industries. However, magnesium alloys face challenges like poor wear resistance and mechanical strength. To overcome these limitations, a promising approach involves developing heterogeneous hybrid microstructures through reinforcement addition and microstructural engineering. This study focuses on the tribological performance of a newly developed in-situ sub-micron sized TiB2/ZE41 composite under various microstructural conditions, comparing it to the unreinforced ZE41 Mg alloy. Wear experiments were conducted using a pin-on-disc tribometer under normal loads of 10, 20, 40, and 60 N at a sliding velocity of 1 m/s. Scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) was used to analyze the worn surfaces in order to identify damage types and surface distortions. By correlating worn surface microstructures with test parameters, predominant wear mechanisms for each material condition under specific loads were determined. Results consistently showed that the presence of in-situ TiB2 reinforcements, β-phase, and rare-earth precipitates enhanced wear resistance regardless of the load conditions. Additionally, the study established a scientific understanding of the wear behavior of ZE41 Mg alloy, with and without in-situ TiB2 particles and precipitates, through analysis of dominant wear mechanisms, wear-induced subsurface deformation mechanisms, kernel average misorientation, grain orientation spread, and microhardness evaluation.

Parallel two‐scale finite element implementation of a system with varying microstructure

AbstractWe propose a two‐scale finite element method designed for heterogeneous microstructures. Our approach exploits domain diffeomorphisms between the microscopic structures to gain computational efficiency. By using a conveniently constructed pullback operator, we are able to model the different microscopic domains as macroscopically dependent deformations of a reference domain. This allows for a relatively simple finite element framework to approximate the underlying system of partial differential equations with a parallel computational structure. We apply this technique to a model problem where we focus on transport in plant tissues. We illustrate the accuracy of the implementation with convergence benchmarks and show satisfactory parallelization speed‐ups. We further highlight the effect of the heterogeneous microscopic structure on the output of the two‐scale systems. Our implementation (publicly available on GitHub) builds on the deal.II FEM library. Application of this technique allows for an increased capacity of microscopic detail in multiscale modeling, while keeping running costs manageable.

Evolution of Graded Surface Microstructure and Property of Ti6Al4V Threads Processed by Surface Rolling

The surface rolling process is important for the forming property of titanium alloy bolts. This study systematically investigated the evolution of the surface microstructure and property of Ti6Al4V threads induced by surface rolling processes with different feeding times. Gradient surface microstructure and property, as characterized by the depth-dependent variations of refined and deformed grains and hardness, were revealed. A comparative analysis of the microstructure and property of the topmost and subsurface layers in different characteristic areas (root, flank, and crest) of the thread was specifically carried out. The surface microstructure and properties are highly heterogeneous in different areas of the rolled thread. Meanwhile, a gradient microstructure and hardness along the depth from the surface was revealed in the surface layer. Our results showed that the highly heterogeneous surface microstructure and property can be attributed to the close correlation between the different stress/strain levels at different depths from the surface and the different deformation mechanisms in the characteristic surface areas of the thread. The present study has indicated that the distinctive microstructure and property in the different characteristic areas of the rolled thread should be featured by those of surface layers at different depths.