Identical Microstructures Research Articles

A novel method of induction electrode through-mask electrochemical micromachining

Through-mask electrochemical micromachining (TMEMM) is a key method for fabricating metal microstructures. However, the accuracy of TMEMM often falls short of the stringent requirements for many applications, primarily due to the uncontrolled electric field during the machining process. To overcome this limitation, this paper introduces a novel method: induction electrode through-mask electrochemical micromachining (IETMEMM). In this method, two feeder electrodes act as the anode and cathode, generating an electric field where the wireless workpiece is placed. This study explores the principles of electric field control in IETMEMM and develops a simulation model to highlight the method's unique advantages under specific electric field distributions. The findings indicate substantial improvements. Leveraging the self-stopping feature, a MEMS inertial switch was fabricated with high accuracy, achieving a non-uniformity of just 3.8%—a remarkable 96.2 % enhancement in accuracy compared to traditional TMEMM. Additionally, the gradient etching advantage facilitated the creation of both gradient-depth and V-shaped microchannel arrays. Moreover, the parallel machining advantage enabled the simultaneous fabrication of three identical microstructures in just 20 s. These outcomes demonstrate the significant potential of IETMEMM for industrial applications.

Elucidating the effects of surface wettability on boiling heat transfer using hydrophilic and hydrophobic surfaces with laser-etched microchannels

This study explores the nuanced interplay between surface wettability and morphology in nucleate boiling heat transfer. Surfaces with identical microstructures but varying wettability are created on copper substrates using laser texturing and a hydrophobic agent. The spacing between laser-etched microchannels is adjusted to achieve different contact angles and percentages of laser-textured areas. Boiling performance is assessed with variations in channel spacing and surface coverage, revealing significant differences between hydrophilic and hydrophobic surfaces. The critical heat flux (CHF) enhancement mechanisms are identified, emphasizing either enhanced liquid replenishment or separate boiling and liquid-supply regions. A critical laser line spacing of 100 μm is determined, where hydrophobic and hydrophilic variants exhibit similar CHF. Interestingly, hydrophilic surfaces show a weak correlation between the heat transfer coefficient (HTC) and contact angle, while hydrophobic surfaces demonstrate a strong correlation. This separation of surface morphology and wettability confirms that lower wettability promotes early nucleate boiling and high HTC, whereas hydrophilic variants contribute to enhanced CHF with lower HTC. These distinctions are most prominent at high coverage with laser-textured areas and diminish as coverage decreases. The findings provide valuable insights into optimizing surface properties for efficient boiling heat transfer applications.

Organic matter influence on ooid formation: New insights into classic examples (Great Salt Lake, USA; Triassic Germanic Basin, Germany)

ABSTRACTOoids are coated grains composed of a tangential or radial cortex growing around a nucleus. They are common in carbonate deposits of almost any geological age and provide insights into environmental conditions. However, abiotic or biotic factors influencing their formation remain unclear. This study aims to advance current understanding of ooid formation with a multi‐analytical approach (for example, field emission scanning electron microscopy, Raman spectroscopy and micro X‐ray fluorescence) to classic examples from Great Salt Lake, USA, and the Lower Triassic Germanic Buntsandstein Basin, Germany. Both of these deposits represent hypersaline shallow‐water environments where ooids are closely associated with microbial mats. Great Salt Lake ooids are dominantly 0.2 to 1.0 mm in size, ellipsoidal to subspherical in shape, composed of aragonite and contain organic matter. Germanic Buntsandstein Basin ooids are mainly ≤4 mm in size, spherical to subspherical in shape, composed of calcite and currently contain little organic matter. Despite the differences, both ooids have the same cortex structures, likely reflecting similar formation processes. Some Great Salt Lake ooids formed around detrital grains while others exhibit micritic particles in their nuclei. In Germanic Basin ooids, detrital nuclei are rare, despite the abundance of siliciclastic particles of various sizes in the host rocks. Germanic Basin deposits also include ‘compound ooids’, i.e. adjacent ooids that coalesced with one another during growth, suggesting static in situ development, which is supported by the lack of detrital grains as nuclei. Germanic Basin ooids also grew into laminated microbial crusts with identical microstructures, further indicating a static formation. Such microbial crusts typically form through mineral precipitation associated with organic matter (for example, extracellular polymeric substances), suggesting a similar formation pathway for ooids. The inferred key‐role of organic matter is further supported by features in radial ooids from the Great Salt Lake, which commonly exhibit, from their nuclei towards their surface, increasing organic matter contents and decreasing calcification.

Effect of Particle Size Distribution on the Printing Quality and Tensile Properties of Ti-6Al-4V Alloy Produced by LPBF Process

The efficiency of the fabrication and the cost of feedstock materials are important constraining factors for a wider application of the laser powder bed fusion (LPBF) process in the industry. Therefore, it is necessary to investigate the feasibility of using different particle size distributions (PSD) combined with higher layer thickness for achieving higher building efficiency and cost-effectiveness. This paper focuses on the effect of PSD (0–53, 15–53, 15–75, and 15–105 μm) on the print quality and mechanical properties of the LPBF-processed Ti-6Al-4V at a layer thickness of 60 μm. The results show that volumetric energy density (VED) range, which allows the coarse powder to reach full density, becomes relatively narrower but is still capable of producing fully dense parts when the parameters are properly adjusted. Among the fully dense specimens, the surface roughness varies slightly with the increase of VED and PSD. In the case of proper parameter selection, specimens made of coarse powder can still achieve low surface roughness. Only slight differences in mechanical performance are found for specimens produced using different PSD powders as they have almost identical microstructures. The issue of the anisotropic mechanical properties of the as-built specimens is resolved after annealing treatment at 800 °C for 2 h. This study provides a guideline for producing high-quality Ti-6Al-4V parts using a higher layer thickness and coarser powders.

The influence of martensitic microstructure and oxide inclusions on the toughness of simulated reheated 10 wt% Ni steel weld metal multi-pass fusion zones

The influence of the effective grain size of the martensitic microstructure and the presence of oxide inclusions on the toughness of a novel high strength, high toughness 10 wt% Ni steel weld metal was investigated. Previously, it was determined that welds produced with the gas tungsten arc welding (GTAW) process exhibited superior toughness to those produced using gas metal arc welding (GMAW), and differences in the martensitic microstructure and oxide inclusion content were identified between the two welds. To elucidate the effect of these two microstructural constituents on toughness, multi-pass weld reheat simulations were performed using a Gleeble 3500 thermal-mechanical simulator designed to produce identical martensitic microstructures in GTAW and GMAW specimens. The GMAW reheat specimens contained a large presence of oxide inclusions from the use of a 98% Ar/2% O2 shielding gas used during welding, whereas the GTAW specimens exhibited a smaller quantity since 100% Ar was used as the shielding gas. These reheat experiments demonstrate that even when both welds have a fine martensitic microstructure, a known toughening mechanism, the toughness of the GMAW is still significantly lower than the GTAW. Thus, the oxide inclusions are the main influence in the lower toughness of the as-welded GMAW, and microstructural refinement is the secondary influence. However, the superior toughness of the GTAW is not only from the lower quantity of oxide inclusions, because when the effective grain size of the GTAW is coarse, the toughness is very low. Thus, both influences are necessary for high toughness of the as-welded GTAW. These results are significant in that they demonstrate the necessity of developing an oxygen-free shielding gas to improve the toughness of welds produced with the GMAW process. The results also now allow for welding procedures to be developed in such a way to avoid low toughness regions in welds produced with both processes, based on the scientific foundation that has been laid here.

Wetting and adhesion energy of droplets on wettability gradient surfaces

Wettability gradient surfaces can be used for heat and mass transfer in many fields, which has aroused extensive interest of research. However, since numerous studies only focused on the surfaces with identical microstructures, the wetting and adhesion energy of droplets on wettability gradient surfaces are still unclear. In this work, three types of microstructured surfaces with gradient wettability were fabricated via photolithography and etching methods. We found that the contact angle, contact angle hysteresis and critical sliding angle will increase with area fraction. Meanwhile, the gradient microstructures will affect the triple line and wetted area of droplets. In addition, it is found that the critical sliding angle depends on not only the droplet volume but the size and types of microstructures, which is consistent with our force analysis. Based on the morphological characteristics and actual wetted area of droplets, an adhesion energy model for microstructured surfaces with gradient wettability is proposed. The model is also verified by other types of wettability gradient surfaces, which may be helpful to design wettability gradient surfaces with low adhesion energy for practical applications.

The effects of quartz Dauphiné twinning on strain localization in a mid-crustal shear zone

We use microstructural, electron backscatter diffraction (EBSD), and crystal vorticity axis (CVA) analyses to evaluate the effects of quartz Dauphiné twinning on strain localization. We compare a granodiorite mylonite and a tonalite mylonite from the Grebe Shear Zone, a mid-crustal transpressional shear zone in Fiordland, New Zealand. EBSD analysis reveals identical quartz grain boundary migration dynamic recrystallization microstructures in both samples, with abundant Dauphiné twinning only in the granodiorite mylonite. Bulk CVA patterns further distinguish the untwinned and Dauphiné-twinned samples, indicating a transition from simple shear-to pure shear-dominated transpression, respectively. The quartz CVA pattern from the Dauphiné-twinned sample indicates that twinned and untwinned grains record a transition from simple shear-to pure shear-dominated deformation, respectively. Pole figures of the Dauphiné-twinned sample reveal high-temperature slip systems in the untwinned and Dauphiné-twinned grains. We conclude that Dauphiné twinning formed early in transpression, and rendered the twinned grains less deformable relative to the untwinned grains over time. The effectiveness of Dauphiné twinning in localizing strain is therefore strongly influenced by its timing relative to the evolving shear zone kinematic deformation geometry.

In vitro digestion of complex foods: How microstructure influences food disintegration and micronutrient bioaccessibility.

Digestion is a mechanical and chemical process that is only partly understood, and even less so for complex foods. In particular, the issue of the impact of food structure on the digestion process is still unresolved. In this study, the fate of four micronutrient-enriched foods with identical compositions but different microstructures (Custard, Pudding, Sponge cake, Biscuit) was investigated using the 3-phase in vitro model of human digestion developed by the INFOGEST network. Matrix disintegration and hydrolysis of macronutrients (proteins, lipids and carbohydrates) were monitored during the three phases of digestion using biochemical techniques, size-exclusion chromatography, thin-layer chromatography and gas chromatography. Micronutrient release (vitamin B9 and lutein) was monitored using reverse-phase chromatography. Food structure did not greatly influence macronutrient hydrolysis, except for lipolysis that was four-times higher for Biscuit compared to Custard. However, the bioaccessibility of both micronutrients depended on the food structure and on the micronutrient. Vitamin B9 release was faster for Biscuit and Sponge cake during the gastric phase, whereas lutein release was higher for Custard during the intestinal step. Extensive statistical analysis highlighted the impact of food structure on the digestion process, with different digestion pathways depending on the food matrix. It also made it possible to characterise the gastric step as a predominantly macronutrient solubilisation phase, and the intestinal step as a predominantly hydrolysis phase.

Stress Localization Resulting from Grain Boundary Dislocation Interactions in Relaxed and Defective Grain Boundaries

Large-scale molecular dynamics simulations are used to study strain and stress localization in atomistic polycrystalline FCC digital samples in a thin-film configuration, deformed in tension. Special focus is placed on the effects of additional grain boundary disorder on the dislocation–grain boundary interaction. The development of the localized stress and strain regions is studied as dislocations are emitted from and arrive at grain boundaries. Digital samples with two different degrees of disorder in the grain boundaries but otherwise identical microstructures are compared in order to understand the effects of additional defects on the stress concentration that develops at the grain boundaries. Localization phenomena are found to depend on the details of the grain boundary defect structure and relaxation state. The results clearly show that the samples with more disordered grain boundaries are more prone to strain and stress localization, with a higher fraction of atoms experiencing extreme deformation. The simulation results are validated by comparison with the predictions of continuum theories and experimental measurements of localized stress performed in austenitic stainless steel.

Role of Mg2Si precipitates size in determining the ductility of A357 cast alloy

This study evaluates the heat treatment effects on microstructural and mechanical properties of A357 alloy. Solution treatments performed at 540 °C for 6, 8, and 10 h represent identical microstructures and show that the eutectic phase is partially dissolved into the matrix, resulting in Si particles of similar shape and size. Contrarily, heat treatment parameters influence Mg2Si precipitates length rather considerably; 8 h solution treated-peak aged condition produces the smallest sized needle-shaped βʺ precipitates and contributes principally in the achievement of higher ductility. It is identified that over-aging not only enhances the length of the precipitates; however, it also causes the partial transformation of needle-shaped βʺ into rod type βʹ precipitates. This phenomenon is the core reason for the reduction in hardness and ductility simultaneously, while enhancement in strength characteristics slightly upon over-aging. Entropy values of differential scanning calorimetry thermograms and calculated dimples diameter of fractured surfaces are fairly aligned with mechanical properties and agree with microstructural characterizations of nano-sized precipitates analyses. Developed relationships among precipitates size (length), ductility, and quality index indicate that precipitation mechanism does not merely contribute to the achievement of superior strength properties; nevertheless, it also plays a crucial role in determining the ductility of A357 cast alloy.

Parallel Process 3D Metal Microprinting

Abstract3D printing, as an additive manufacturing technology, enables agile and free‐form fabrication of complex 3D structures relevant to industrial application. However, the 3D structure forming mechanisms in existing 3D printing technologies hinder and even prevent the manufacturing of ultra‐precision 3D metal parts, let alone parallel process manufacturing. A generic 3D electrochemical microprinting technology that allowed the “printing” of ultrahigh density, ultrahigh aspect ratio, and electronics quality 3D copper structures with microscale and even nanoscale precision in an ambient environment is developed here. Further on, the feedback‐controlled and self‐regulated “printing” mechanism was demonstrated to be capable of realizing parallel process 3D “printing” of an array of identical copper microstructures simultaneously, promising large‐scale 3D printing–based production of precision metal structures for broad applications in 3D integration of electronics and sensor systems.

An efficient full-field crystal plasticity-based M–K framework to study the effect of 3D microstructural features on the formability of polycrystalline materials

In this paper, the new rate tangent–fast Fourier transform-based elasto-viscoplastic crystal plasticity (CP) constitutive framework (RTCP-FFT) developed by Nagra et al (2017 Int. J. Plast. 98 65–82) is implemented in the so-called Marciniak–Kuczynski (M–K) (Marciniak and Kuczyński 1967 Int. J. Mech. Sci. 9 609–20) framework to predict the forming limit diagrams (FLDs) of face-centered cubic polycrystals. The RTCP-FFT approach that accounts for 3D grain morphologies and grain interactions is used to compute the FLDs for aluminum alloys (AAs). The model employs two statistically representative volume elements with identical initial microstructures, one inside the imperfection band region (required for M–K analysis) and other outside the imperfection band region of the sheet metal. The proposed RTCP-FFT-based M–K model is a full-field, mesh-free and efficient CP formulation that enables a comprehensive investigation of the effects of 3D microstructural features on the FLDs with extremely small computational times. The new model is validated by comparing the predicted FLDs for AA5754 and AA3003 AAs with experimental measurements. Furthermore, the predicted FLDs are compared with the well-known Taylor-type homogenization scheme-based M–K model (MK–Taylor) predictions. Furthermore, the effects of different grain shapes as well as local grain interactions on the FLD predictions are studied. The study reveals that among the various microstructural features, the grain morphology has the strongest effect on the predicted FLDs and the FLD predictions can be significantly improved if the actual grain structure of the material is properly accounted for in the numerical models.

Influence of Boron on Austenite to Ferrite Transformation Behavior of Low Carbon Steel Under Continuous Cooling

In the current work, the influence of boron on austenite to ferrite transformation behavior under continuous cooling condition and its associated features, e.g., final microstructure, mechanical properties, etc., in low carbon steel has been studied. The steels (C 0.04 wt.%, B 10-100 ppm) prepared in an open air laboratory furnace showed identical microstructures having ferrite grains of 20-25 µm. However, tensile test data indicate variation of yield strength and ultimate tensile strength with boron content. The yield point elongation and strain aging index both were found to decrease with increase in boron content or boron-to-nitrogen ratio. As the boron nitride precipitates stimulate the nucleation of ferrite phase, the dilation curves show an increase in austenite to ferrite transformation start temperature with boron content. The resulting microstructure and hardness value also corroborate the finding. Transmission electron microscopy findings revealed the presence of ultra-fine boron nitride (BN) precipitates in both grain boundary and grain body of the steel having boron concentration of 30 ppm and beyond. The presence of these precipitates also increased with boron content. Based on austenite decomposition behavior, related microstructure and hardness values it is conjectured that these BN precipitates may act as nucleating agent for polygonal ferrite during austenite decomposition, thereby softening the steel during fast cooling.

Robust topology optimization for cellular composites with hybrid uncertainties

SummaryThis paper will develop a new robust topology optimization method for the concurrent design of cellular composites with an array of identical microstructures subject to random‐interval hybrid uncertainties. A concurrent topology optimization framework is formulated to optimize both the composite macrostructure and the material microstructure. The robust objective function is defined based on the interval mean and interval variance of the corresponding objective function. A new uncertain propagation approach, termed as a hybrid univariate dimension reduction method, is proposed to estimate the interval mean and variance. The sensitivity information of the robust objective function can be obtained after the uncertainty analysis. Several numerical examples are used to validate the effectiveness of the proposed robust topology optimization method.

Interrelationships among microstructures of otoacoustic emissions and hearing thresholds

Otoacoustic emission (OAE) amplitudes, phases, and delays often exhibit ripples with small changes in stimulus frequency. Similar microstructure patterns are observed in behavioral hearing thresholds and loudness judgements for pure tones. Here, we summarize work demonstrating that there is a common microstructure in hearing thresholds and OAEs elicited by single tones—referred to as stimulus-frequency OAEs (SFOAEs)—when presented at near-threshold levels. The periodicity and strength of this microstructure are related to SFOAE delay and magnitude, respectively. Such relationships are consistent with this microstructure arising from multiple intracochlear reflections of SFOAE energy between its region of generation and the middle ear boundary—an idea proposed by David Kemp in his first reports describing the discovery of emissions from the ear. The details of OAE generation and propagation explain why similar but not identical microstructures are also observed in the ear canal pressure in response to tones (which is the vector sum of the stimulus and SFOAE pressures) and in two-tone evoked distortion-product OAE spectra, as well as why microstructures shift in frequency as the result of cochlear or middle ear manipulations.Otoacoustic emission (OAE) amplitudes, phases, and delays often exhibit ripples with small changes in stimulus frequency. Similar microstructure patterns are observed in behavioral hearing thresholds and loudness judgements for pure tones. Here, we summarize work demonstrating that there is a common microstructure in hearing thresholds and OAEs elicited by single tones—referred to as stimulus-frequency OAEs (SFOAEs)—when presented at near-threshold levels. The periodicity and strength of this microstructure are related to SFOAE delay and magnitude, respectively. Such relationships are consistent with this microstructure arising from multiple intracochlear reflections of SFOAE energy between its region of generation and the middle ear boundary—an idea proposed by David Kemp in his first reports describing the discovery of emissions from the ear. The details of OAE generation and propagation explain why similar but not identical microstructures are also observed in the ear canal pressure in response to tone...

Influence of Nonuniform Micron-Scale Strain Distributions on the Electrical Reorientation of Magnetic Microstructures in a Composite Multiferroic Heterostructure

Composite multiferroic systems, consisting of a piezoelectric substrate coupled with a ferromagnetic thin film, are of great interest from a technological point of view because they offer a path toward the development of ultralow power magnetoelectric devices. The key aspect of those systems is the possibility to control magnetization via an electric field, relying on the magneto-elastic coupling at the interface between the piezoelectric and the ferromagnetic components. Accordingly, a direct measurement of both the electrically induced magnetic behavior and of the piezo-strain driving such behavior is crucial for better understanding and further developing these materials systems. In this work, we measure and characterize the micron-scale strain and magnetic response, as a function of an applied electric field, in a composite multiferroic system composed of 1 and 2 μm squares of Ni fabricated on a prepoled [Pb(Mg1/3Nb2/3)O3]0.69-[PbTiO3]0.31 (PMN-PT) single crystal substrate by X-ray microdiffraction and X-ray photoemission electron microscopy, respectively. These two complementary measurements of the same area on the sample indicate the presence of a nonuniform strain which strongly influences the reorientation of the magnetic state within identical Ni microstructures along the surface of the sample. Micromagnetic simulations confirm these experimental observations. This study emphasizes the critical importance of surface and interface engineering on the micron-scale in composite multiferroic structures and introduces a robust method to characterize future devices on these length scales.

Topology optimization for concurrent design of structures with multi-patch microstructures by level sets

This paper focuses on the novel concurrent design for cellular structures consisting of multiple patches of material microstructures using a level set-based topological shape optimization method. The macro structure is featured with the configuration of a cluster of non-uniformly distributed patches, while each patch hosts a number of identical material microstructures. At macro scale, a discrete element density based approach is presented to generate an overall structural layout involving different groups of discrete element densities. At micro scale, each macro element is regarded as an individual microstructure with a discrete intermediate density. Hence, all the macro elements with the same discrete densities (volume fractions) are represented by a unique microstructure. The representative microstructures corresponding to different density groups are topologically optimized by incorporating the numerical homogenization approach into a parametric level set method. The multiscale concurrent designs are integrated into a uniform optimization procedure, so as to optimize both topologies for the macrostructure and its microstructures, as well as locations of the microstructures in the design space. Numerical examples demonstrate that the proposed method can substantially improve the structural performance with an affordable computation and manufacturing cost.

Micro-Nanostructures of Cellulose-Collagen for Critical Sized Bone Defect Healing.

Bone tissue engineering strategies utilize biodegradable polymeric matrices alone or in combination with cells and factors to provide mechanical support to bone, while promoting cell proliferation, differentiation, and tissue ingrowth. The performance of mechanically competent, micro-nanostructured polymeric matrices, in combination with bone marrow stromal cells (BMSCs), is evaluated in a critical sized bone defect. Cellulose acetate (CA) is used to fabricate a porous microstructured matrix. Type I collagen is then allowed to self-assemble on these microstructures to create a natural polymer-based, micro-nanostructured matrix (CAc). Poly (lactic-co-glycolic acid) matrices with identical microstructures serve as controls. Significantly higher number of implanted host cells are distributed in the natural polymer based micro-nanostructures with greater bone density and more uniform cell distribution. Additionally, a twofold increase in collagen content is observed with natural polymer based scaffolds. This study establishes the benefits of natural polymer derived micro-nanostructures in combination with donor derived BMSCs to repair and regenerate critical sized bone defects. Natural polymer based materials with mechanically competent micro-nanostructures may serve as an alternative material platform for bone regeneration.

Interface microstructure formation of dissimilar Fe/Fe–Mn–C steel RSW joints

An experiment was developed to simulate the interface between liquid high manganese carbon steel and solid ultra-low alloyed steel in a thermal gradient, corresponding to the nugget/sheet interface of resistance spot welds. Despite the large difference in the interaction time between the experiment and the welding process, identical microstructures and phases were observed in both. The time and temperature control of the experimental set-up indicates that the solute diffusion in the solid and liquid phase together with the interface temperature when cooling determines the microstructure formation and morphology. The presence of ϵ-martensite requires a γ/liquid interface with a manganese-driven dissolution. A criterion based on manganese supersaturation is proposed and shows that with the studied steels the nucleation and growth of ϵ-martensite is almost unavoidable when using resistance spot welding. The cellular patterns observed during solutal melting at low interface temperature increase the interface surface and the amount of martensite. The origin of the cells is the carbon enrichment in the manganese diffusion zone of the γ phase that provokes a solidus temperature gradient in the thermal gradient.

Concept of non-periodic metasurfaces based on positional gradients applied to IR-flat lenses

We describe a theoretical study of gradient metasurfaces that – unlike most theoretical designs requiring advanced fabrication techniques – could easily be produced by a simple patterning method, templated microlens lithography (TEMPL). We show here that positional gradients of identical microstructures can lead to a gradient of phase lag across the metasurface. Using a radial gradient in the pitch of a hexagonal array of identical microfabricated resonators, one could thus produce gradient metasurfaces with the ability to focus infrared light. We provide illustrative examples of devices and compare their theoretical capabilities.