Fine-grained Samples Research Articles

Unveiling microstructural evolution and its effect on mechanical performance in a Cu-9Ni-6Sn alloy

Cu-9Ni-6Sn alloy exhibits profoundly potential as a new environmental-friendly conductive elastic material. In this work, the formation and growth mechanism of discontinuous precipitation, as well as its effect on mechanical properties of Cu-9Ni-6Sn alloy are systematically studied. The investigation indicated that the discontinuous precipitation does easily initiate from random grain boundaries but showing opposite result for Σ3 boundaries. The lower frequency Σ3 boundaries relatively, the more intense the solute diffusion, resulting in a higher volume fraction of discontinuous precipitation. The increasing aging temperature and time will accelerate the grain boundary discontinuous reaction, and the fine-grained samples exhibit a higher volume fraction of discontinuous precipitates and smaller lamellar spacing due to the more nucleation sites and increased interfacial energy. The strengthening mechanism of Cu-9Ni-6Sn alloy mainly focus on dislocation strengthening and precipitation strengthening, in which the D022 or L12-γ′ phases exhibit more significantly precipitation strengthening effect but is difficult to guarantee ductility. The localized grain boundary discontinuous precipitation detrimentally affect both the tensile strength and ductility.But the nano-lamellar discontinuous precipitation is beneficial to the strength-ductility trade off when it occupies the entirely Cu matrix. This work establishes a robust foundation for the microstructural optimization and multi-component design of Cu-9Ni-6Sn alloy.

Grain size effect on stress-induced martensite in a metastable β-Ti alloy with ultrahigh strength and strain hardening rate

In the present work, the influence of β grain size on stress-induced martensite (SIM) was investigated in a metastable β-Ti alloy (Ti-4Mo-3Cr-1Fe-1Al). Samples with varying grain sizes were prepared by cold rolling and annealing. The triggering stress for SIM decreases with the grain size increase from 44 μm to 180 μm. Meanwhile, the yield strength increases with decreasing grain size, consistent with the Hall-Petch effect. Fine-grained samples formed a greater number of martensitic bands during deformation compared to coarse-grained samples, resulting in an ultra-high strain-hardening rate ∼4320 MPa. The deformation mechanism of the Ti-4Mo-3Cr-1Fe-1Al alloy consists of the ω to β transformation, SIM, martensite deformation twinning ({110}cc < 1–10>α" and {130}<-310>α" twins), reorientation of martensite and dislocation slip. Both the 44 μm and 59 μm samples exhibit ultra-high true tensile strengths (>1200 MPa), with a large work-hardening interval of nearly 600 MPa relative to the yield strength. This significant work-hardening capability is attributed to interfacial and dislocation strengthening arising from the dynamic formation of martensitic bands during deformation.

Investigation of fracture mechanical properties of a brass alloy with microstructural variations

This study investigates the effect of microstructural variations on the mechanical properties of CuZn35Mn2Al1Fe1-C-GS brass alloy. Specimens taken from positions with different cooling rates in a large cast component exhibit coarse-grained (approximately 5mm) and fine-grained (approximately 1mm) microstructures. Fine-grained samples demonstrate at least a 7% increase in Ultimate Tensile Strength (UTS) and up to a 33% higher long crack threshold ΔKth,lc. Hardness measurements are similar between microstructures. The NASGRO model and cyclic R-curve are applied to fit crack propagation data, and fractographic analysis reveals distinct fracture mechanisms. The results indicate that a fine-grained microstructure enhances tensile strength and crack resistance, providing valuable insights for the design and maintenance of heavy machinery components made from cast brass.

Enhancing Iron Ore Grindability through Hybrid Thermal-Mechanical Pretreatment

Grinding is an important process of ore beneficiation that consumes a significant amount of energy. Pretreating ore before grinding has been proposed to improve ore grindability, reduce comminution energy, and enhance downstream operations. This paper investigates hybrid thermal mechanical pretreatment to improve iron ore grinding behavior. Thermal pretreatment was performed using conventional and microwave approaches, while mechanical pretreatment was conducted with a pressure device using a piston die. Results indicate that conventional (heating rate: 10 °C; maximum temperature: 400 °C), microwave (2.45 GHz, 1.7 kW, 60 s), and mechanical (14.86 MPa, zero delay time) pretreatments improved the studied iron ore grindability by 4.6, 19.8, and 15.4%, respectively. Meanwhile, conventional-mechanical and microwave-mechanical pretreatments enhanced the studied iron ore grindability by 19.2% and 22.6%, respectively. These results suggest that stand-alone mechanical pretreatment or microwave pretreatment may be more beneficial in improving the grinding behavior of the studied fine-grain iron ore sample. The results of the mechanical pretreatment obtained in this study may be used in a simulation of the HPGR system for grinding operations of similar iron ore

On the plastic deformation mechanism of Al0.6CoCrFeNi high entropy alloy: In-situ EBSD study and crystal plasticity modeling

In this study, in-situ tensile tests with electron back-scattered diffraction (EBSD) were conducted to reveal the microstructural effects on the plastic deformation behavior of dual-phase Al0.6CoCrFeNi high entropy alloys (HEAs). The in-situ EBSD results demonstrated a uniform distribution of dislocation density in the fine grain (FG) samples, whereas high dislocation density was predominantly localized near body-centered cubic (BCC) phases in the coarse grain (CG) samples. The difference in mechanical properties between face-centered cubic (FCC) and BCC phases caused stress concentration and cracking at the boundaries during tension. The FCC phase within FG samples exhibited excellent plasticity, effectively impeding the propagation and coalescence of microcracks emanating from the BCC phase into longer cracks. For CG samples, brittle cracks formed in BCC phases are easy to merge, thus evolving into long cracks. Crystal plasticity finite element analysis revealed that as the strain increases, stress distribution in FG samples tended to become more homogeneous, whereas for CG samples high stress concentration consistently occurred within BCC phases. The deformation characteristics of FG were attributed to the synergistic effect generated by the FCC phase with heterogeneous grain size and the BCC phase characterized by small grain size.

Effect of grain size on spall fracture of CrCoNi medium-entropy alloy under Taylor-wave loading

The effect of grain size on spall properties of medium-entropy alloy CrCoNi under Taylor-wave loading is investigated. Three different grain sizes, 300 μm, 20 μm, and 3 μm, are explored. The free surface velocity histories are measured to obtain such quantities as dynamic yield strength and spall strength. With decreasing grain size, there is a slight decrease in spall strength, but a significant increase in damage rate. The shock-recovered samples are characterized with scanning electron microscopy and electron backscatter diffraction. In coarse-grained samples, voids tend to nucleate within grain interiors, while in fine-grained samples, voids nucleate preferentially at grain boundaries (GBs). Molecular dynamics simulations show that the nucleation of intergranular or intragranular voids is dominated by GB–slip and slip–slip intersections, respectively. The higher GB density results in more extensive GB–slip intersections, consistent with the experimental results.

Optimizing Micro-CT Resolution for Geothermal Reservoir Characterization in the Pannonian Basin

In the context of global efforts to transition toward renewable energy and reduce greenhouse gas emissions, geothermal energy is increasingly recognized as a viable and sustainable option. This paper presents a comprehensive assessment derived from a subset of a larger sample collection within the Dunántúli Group of the Pannonian Basin, Hungary, focusing on optimizing micro-computed tomography (µ-CT) resolution for analyzing pore structures in sandstone formations. By categorizing samples based on geological properties and selecting representatives from each group, the study integrates helium porosity and gas permeability measurements with µ-CT imaging at various resolutions (5 µm, 2 µm, and 1 µm). The findings reveal that µ-CT resolution significantly affects the discernibility and characterization of pore structures. Finer resolutions (2 µm and 1 µm) effectively uncovered interconnected pore networks in medium- to coarse-grained sandstones, suggesting favorable properties for geothermal applications. In contrast, fine-grained samples showed limitations in geothermal applicability at higher resolutions due to their compact nature and minimal pore connectivity, which could not be confidently imaged at 1 µm. Additionally, this study acknowledges the challenges in delineating the boundaries within the Dunántúli Group formations, which adds a layer of complexity to the characterization process. The research highlights the importance of aligning µ-CT findings with geological backgrounds and laboratory measurements for accurate pore structure interpretation in heterogeneous formations. By contributing vital petrophysical data for the Dunántúli Group and the Pannonian Basin, this study provides key insights for selecting appropriate µ-CT imaging resolutions to advance sustainable geothermal energy strategies in the region. The outcomes of this research form the basis for future studies aimed at developing experimental setups to investigate physical clogging and enhance geothermal exploitation methods, crucial for the sustainable development of geothermal resources in the Pannonian Basin.

HDNet: Human-like discrimination with visual key for few-shot cross-domain object detection

Most existing few-shot object detection (FSD) methods implicitly assume that the target domain data with few samples conform to the same statistical distribution as the source domain. However, this assumption is impractical, especially when dealing with unconstrained scenarios. Also, the decline of fine-grained hidden samples caused by scene switching, significant morphological changes, etc. has brought great challenges to object detection. To solve the above few-shot cross-domain detection (FS-CDD) problems, in this work, we propose a novel and flexible Human-like Discrimination Network (HDNet), which is composed of four modules. Firstly, multi-level key generation (MKG) fully mining multi-level comprehensive abstract representation. The precious knowledge that contains diverse low and high levels is obtained by three parallel branches. After decoupling the hidden space, the rich patches from each pair of target and source domains are closely matched in the Embedded Space Implicit Association (ESIA) using degree description. In order to enhance the discriminative capability of the model for a few samples, the instances are additionally encoded and corrected at the classification end using the Prediction head with instance embedding (PHIE). Finally, the Adaptive Reweighted Module (ARM) is redesigned to determine coefficient of multiple loss functions, which avoids the improper operation of setting coefficients according to experience in the past. Extensive experiments demonstrate that despite the dual challenges of limited samples and cross-domain scenarios, the proposed HDNet exhibits remarkable performance.

Architecting strength: Innovative microstructural design of Aluminum/Alumina Nanocomposites via cold-welded flaky-shaped particles and pressure-assisted sintering

Aluminum/alumina (Al/ Al2O3) nanocomposites with three different microstructural architectures were prepared using flake powder metallurgy, which involves the conversion of spherical Al powder into nanoflakes by ball milling, the introduction of Al2O3 by natural oxidation, the control of the powder microstructure by cold welding, and then powder by densification, sintering, and extrusion. The experimental results showed that the shape of the Al matrix grains and the distribution of native Al2O3, the so-called Al/Al2O3 architectures, could be precisely controlled by BM. The nanolaminate architecture, in which the Al2O3 nanoplatelets were aligned along the boundaries of lamellar or elongated grains, exhibited a more balanced combination of tensile strength and ductility than the random architecture with non-uniformly distributed Al2O3 nanoplatelets within equiaxed grains. This improvement can be attributed to the combined effect of higher Al2O3 strengthening efficiency and better work hardening ability. The research results suggest that the presence of Al2O3 nanoplatelets at high-angle grain boundaries significantly hinders the main mechanism of subgrain rotation for the formation of new boundaries. Moreover, the simulation accurately predicts the higher degree of grain faceting in finer-grained samples, which is consistent with the experimental data indicating more pronounced hexagonal grain shapes. Consequently, flake powder metallurgy offers a promising approach for the production of strong and ductile Al-matrix composites through the design of their microstructural architecture.

Investigation of radiation tolerance of yttria stabilized zirconia in the ballistic collision regime: Effect of grain size and environmental temperature

The irradiation response of yttria-stabilized zirconia, having different grain sizes, subjected to 900 keV iodine ions at room temperature and 1000 K is reported. GIXRD and Raman spectroscopy indicate superior radiation tolerance of the fine-grained samples when compared to their coarse-grained counterparts which is attributed to the abundance of grain boundaries at relatively shorter distances. A reduction in the residual strain is observed in the samples irradiated at 1000 K. This is attributed to the clustering of the irradiation induced point defects thereby resulting in a decrease in their density, but with a corresponding increase in the extended defects density.

Analysis on the compressive creep behaviors of Mg–Y alloys with various grain sizes

The creep behaviors of a hot-rolled Mg-4.5 wt%Y alloy sheet in the grain size ranging from d = 10 μm to d = 160 μm were carefully investigated in this work. It was shown that both loading direction and grain size exhibited effects on the creep behavior. The creep resistance along the ND was always greater than that along the RD, and the increased grain size contributed to the improved creep resistance along both directions. For the fine-grained samples (d = 10 μm to d = 25 μm), the dominant mechanisms were independent of the loading direction, including grain boundary migration (GBM), cross-slip made by basal dislocations and prismatic dislocations, and <c + a > dislocations slipping on the prismatic planes. The undifferentiated dominant mechanisms led to the extremely low creep anisotropy. For the coarse-grained samples (d = 60 μm to d = 160 μm), the dominant mechanisms were different along two loading directions. Specifically, all RD samples shared the dominant mechanisms of cross-slip and {101‾2} twinning, while the dominant mechanisms of all ND samples were dislocation climb and <c + a > dislocations slipping on pyramidal planes. The easy activation of {101‾2} twinning replaced GBM and induced the creep anisotropy, resulting in a low incremental speed of creep resistance along the RD. Differently, the primary dislocation climb and pyramidal <c + a > slip brought a high incremental speed of creep resistance along the ND. Consequently, the coarsen-grained samples had a strong creep anisotropy.

Soil liquefaction sites following the February 6, 2023, Kahramanmaraş-Türkiye earthquake sequence

AbstractSeismically induced soil liquefaction was listed as one of the major causes of damage observed in the natural and built environment during the 2023 Türkiye-Kahramanmaraş earthquake sequence. Reconnaissance field investigations were performed to collect perishable data and document the extent of damage immediately after the events. The sites with surface manifestations of seismic soil liquefaction in the form of soil ejecta, excessive foundation and ground deformations were identified and documented. The deformations were mapped, and samples from ejecta were retrieved. The ejecta samples were predominantly classified as sands with varying degrees of fines. Laboratory test results performed on liquefied soil ejecta revealed that the fines-containing liquefied ejecta samples are mostly classified as low plasticity clays (CL). Most of CL soil type ejecta were retrieved from Gölbaşı–Adıyaman region. The liquid limits of these samples varied in between 32 and 38%, their plasticity index values were estimated in the range of 16–23%. Surprisingly, two ejecta samples with plasticity indices higher than 30% were retrieved from Hatay airport, one of which was classified as high plasticity clay (CH). The majority of the fine-grained ejecta samples fall either on “Zone B: Testing Recommended” region of the Seed et al. (Keynote presentation, 26th Annual ASCE Los Angeles Geotechnical Spring Seminar, Long Beach, CA, 2003) susceptibility chart. Moreover, 12 out of 74 samples fall outside the susceptible limits defined by Seed et. These preliminary results suggest that clayey soils can produce liquefied ejecta when subjected to cyclic loading. Detailed site investigation and laboratory testing programs are ongoing to further investigate this rather unexpected response. Until their findings become available, the liquefaction susceptibility of silty-clayey soils’ mixtures is recommended to be assessed conservatively with caution.

Evaluation of Damage Stress Thresholds and Mechanical Properties of Granite: New Insights from Digital Image Correlation and GB-FDEM

We employed a novel combination of digital image correlation (DIC) and grain-based hybrid finite–discrete element method (GB-FDEM) to improve the comprehension of the relationships between microstructural features and the mechanical properties of granitic rocks. DIC and numerical results showed that macrocracks initiated and propagated along grain boundaries among different minerals driven by the high stiffness contrast between the compliant biotite and the stiffer feldspar/quartz grains. Surface deformation analyses revealed that tensile-dominated macrocracks open at monotonically increased rates before the crack damage threshold, and the opening accelerated afterwards with the increased shear component. The onset of the acceleration of the opening rate of macrocracks can be used to infer the crack damage threshold. Both strain and acoustic emission were used to infer damage stress thresholds in the synthetic numerical samples. Numerical results showed that the damage stress thresholds and uniaxial compressive strength decrease with increasing grain size following log-linear relations. Coarse-grained samples tend to fail by axial splitting, while fine-grained samples fail by shear zone formation. Biotite and quartz contents significantly affect mechanical properties, while quartz to feldspar ratio is positively related to the mechanical properties. Our study demonstrates the capacities of DIC and GB-FDEM in inferring damage conditions in granitic rocks and clarifies the microstructural control of the macroscopic mechanical behaviors. Our results also provide a comprehensive understanding of the systematics of strain localization, crack development, and acoustic emission during the rock progressive failure process.

Smectite-bitumen interactions in non-aqueous bitumen extraction process

The non-aqueous extraction (NAE) is an alternative to the commercial water-based extraction technology used to liberate bitumen from oil sands. Although the impact of kaolinite, illite, chlorite, illite-smectite and montmorillonite on NAE process has been previously studied, the effect of different types of smectites has not been fully understood yet. In this work, mixtures of bitumen with bentonites dominated by saponite, hectorite, nontronite, beidellite and montmorillonite were reacted for several days and then washed with solvent (cyclohexane) to remove bitumen from the bentonites. The main goal was to better understand the impact of different smectites properties (specific surface area, pore structure characteristics, particle size, crystallite thickness, swelling ability, cation exchange capacity, layer charge and crystal-chemistry of smectites) on NAE process. The results showed that the porosity, particle size and swelling ability were the key parameters affecting the solvent-based bitumen recovery under the studied conditions. Samples with larger initial total pore volume and smaller particle size displayed reduced solvent bitumen extractability. The particle size of studied samples was affected primarily by swelling of smectites during the solvent bitumen extraction experiments. Smectites were swelling in water but not in cyclohexane. Swelling of smectite caused splitting of larger clay particles into many smaller particles. As a consequence, the efficiency of solvent bitumen extraction was significantly lower for fine grained samples, consisting of thin delaminated smectite particles, in which the bitumen was distributed among small-sized clay particles.

Effect of initial grain size on the recrystallization behavior and recrystallization texture of a Mg–3Gd alloy

The effect of initial grain size on the recrystallization and recrystallization texture of a rolled Mg–3Gd (wt.%) alloy is studied in detail. The results show that the deformation microstructure of an initially coarse-grained (CG) sample has a larger twinned area and a higher density of twin boundaries than a fine-grained (FG) sample. After annealing, the CG sample recrystallizes preferentially in the twinned area, whereas the FG sample adopts the higher density grain boundaries as the nucleation sites. Furthermore, weak recrystallization texture components appear from the grain nucleation stage, regardless of the initial grain size, and are preserved after complete recrystallization due to uniform grain growth. The majority of recrystallization texture is deviated 20°–45° away from normal direction (ND), accounting for more than 50 %. Especially, the recrystallization texture of the FG sample is a “Rare Earth texture”, in contrast to the widely reported texture modification unrelated to grain boundary nucleation. Only a scattered basal texture is observed in the CG sample, which also differs from the reported “Rare Earth texture” originating from shear band nucleation in dilute Mg–Gd alloys. Finally, based on the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model, the recrystallization kinetics are calculated, and it is found that the initial grain size mainly affects the nucleation rate, and has limited effect on the grain growth rate.

Synchronizing DDoS detection and mitigation based graph learning with programmable data plane, SDN

The availability of SD-IoT is now under complex and serious cyber threats, especially distributed denial-of-service attacks. However, traditional defense schemes suffer from coarse-grained centralized sampling approaches, low accuracy of detection models, and inefficient mitigation methods. In this paper, a novel DDoS defense scheme is proposed, which consists of a high-accuracy detection mechanism based on a Graph Convolutional Neural Network learning model and a mitigation mechanism based on fast traffic migration. In the detection stage, a fine-grained INT sampling approach is utilized to obtain multidimensional network topology and status information. The Graph Convolutional Neural Network learning model detects switches containing DDoS attack traffic with high accuracy because the detection model not only extracts and utilizes multiple temporal and spatial features of the collected information, but also has a better learning and representation capability. In the mitigation stage, the enhanced whitelist with dynamic threshold-based values is automatically adapted to the real-time state of the network environment for enhanced mitigation flexibility. The fast programmable segment rerouting strategy can block attack traffic in time and ensure the continuity of network services. The results of several comparison experiments show that the proposed scheme can detect DDoS attacks more accurately and mitigate them more effectively than traditional schemes.

Effect of micro-grain casting process on the microstructure and high cycle fatigue properties of K492M alloy at 700 °C

A nickel base polycrystalline superalloy K492M was used as the material in the present study. The samples of K492M alloy were prepared by conventional casting process, fine-grain casting process and micro-grain casting process, respectively, to study the effects of micro-grain casting process on the microstructure and high cycle fatigue property of K492M alloy at 700 °C. The experimental results show that micro-grain casting process can significantly refine grains, reduce solidification segregation and increase γ′ volume fraction. The micro-grain casting K492M sample exhibited a significantly higher high cycle fatigue life at 700 °C, which was improved by 412% and 269% from that of conventional and fine-grain casting samples, respectively. Analysis for fracture sample indicated that fatigue cracks initiated from the persistent slip bands on the surface or subsurface of the sample. In addition, the cracked carbides accelerated the crack propagation and fatigue fracture. The refined grains and carbides by micro-grain casting process significantly slowed down the propagation of fatigue cracks, and thereby improves the fatigue life.

Химическая устойчивость мелкозернистой керамики на основе фосфата Nd0,33Zr2(PO4)3 со структурой коснарита при повышенных температурах

Chemical stability of Nd0.33Zr2(PO4)3 fine-grained ceramics, which can be used for immobilization of REE that are part of the HLW was studied. Single-phase Nd0.33Zr2(PO4)3 submicron powders with the structure of the mineral kosnarite were obtained by colloid-chemical synthesis. Powders were obtained by successive annealing at 600, 800, and 900 °C for 6 h at each stage. Ceramics Nd0.33Zr2(PO4)3 has been obtained by Spark Plasma Sintering (SPS) method. The relative density of ceramics was 89.9 %; the average grain size was 5 – 20 μm. The chemical stability of the ceramics in the static mode at 90 °C in distilled water, mineral waters, as well as in acidic media (0.1 M HCl) and alkaline media (0.01 M NaOH) was studied. Ceramics have high hydrolytic stability. The influence of the contact medium on the rate leaching and mechanism of Nd leaching from the surface of Nd0.33Zr2(PO4)3 fine-grained ceramic samples has been studied. The de Groot-van der Sloot model was used to analyze the obtained time dependences of the leaching rate Ri. Nd leaching in acidic medium occurs due to dissociation of Nd from the ceramic surface, in alkaline medium and mineral water due to diffusion from the inner layers, in distilled water due to the dissolution of the ceramic surface layer.

Effects of grain size and temperature on slip and twinning activity in a magnesium-rare earth alloy

Understanding the deformation mechanisms in magnesium alloys is critical to develop the next-generation high-performance magnesium alloys. In this work, the effects of grain size and temperature on slip and twinning activities in WE43 magnesium-rare earth alloy were investigated with the quasi-in-situ electron backscattering diffraction method and slip trace analysis. Compression tests were conducted for the samples with three different grain sizes at room temperature (RT) and liquid nitrogen temperature (LNT), respectively. More pyramidal slips were activated in the fine-grained sample to accommodate the plastic strain instead of more twins generated in the coarse-grained sample, which contributed to its higher strain to failure and strain hardening rate. Numerous individual twins with thin structures formed in the fine-grained sample, while thick twins were observed in the coarse-grained sample. The numerous thin twins and high activities of pyramidal slips in the fine-grained sample would be attributed to the high kernel average misorientation (KAM) value and local stress concentration around grain boundaries. Regarding temperature effects, more thin twins and twin-twin interactions were observed at LNT than at RT, and the KAM value was high around these twin boundaries, which contributed to enhancing the flow stress but reducing the strain to failure at LNT.

Mechanical and electrical responses of natural-cooled high-temperature granite of different grain sizes

In order to understand the effect of grain size on the mechanical and electrical responses of natural-cooled high-temperature granite, uniaxial compression tests were carried out on natural cooled coarse- and fine-grained granite samples subjected to thermal treatment at room temperature, 200 °C, 400 °C, and 600 °C respectively. The resistivity and acoustic emission (AE) during the compression were monitored and changes in physical and mechanical properties, the AE and resistivity characteristics in the loading process were analyzed. Results show that high temperature exerts a more significant effect on deteriorating the coarse-grained granite. Changes in resistivity can reflect the development of rock damage. Corresponding to the compaction stage, crack initiation and stable propagation stage, and crack rapid propagation stage of rock under compressive load, changes in resistivity can be divided into three stages accordingly, including the initial rapid descent stage, the gentle descent stage, and the secondary rapid descent stage for the thermal-treated rock at 25–400 °C. The secondary rapid descent stage of resistivity can be used as a precursor for rock entering into the failure stage. The resistivity change is more sensitive to the damage development in coarse-grained granite.