Influence Of Grain Size Research Articles

Kinetics of Austenite Formation in a Medium-Carbon, Low-Alloy Steel with an Initial Martensite Microstructure: Influence of Prior Austenite Grain Size

The impact of prior austenite grain size (PAGS) on the kinetics of austenite formation with an initial martensite microstructure was investigated in a medium-carbon, low-alloy steel. Two distinct PAGS of 117 and 330 μm, representing the range of grain sizes encountered in industries, were considered. In this analysis, high-resolution dilatometry was used to study the formation of austenite during continuous heating experiments. The analysis of the dilatometry results revealed that grain refinement accelerated the rate of austenite formation without impacting its austenite formation temperature. Intermittent quenching tests were conducted to elucidate the nucleation and growth mechanisms of austenite formation using a combination of optical, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The differences in austenite formation kinetics as a function of prior austenite grain size were quantified and modeled in the framework of diffusion-controlled nucleation and growth theories using the genetic algorithm optimization.

Influence of Hydrogen Peroxide Catalyst Grain Size on Performance and Ageing

Two different diameters of Pt/Al2O3 spherical catalysts (1 mm and 2 mm) for HTP 98% decomposition were tested to compare the catalytic activity and catalyst ageing. Comparable decomposition performance efficiencies were obtained during thruster-like tests in a catalytic decomposition setup, even though the 1-mm showed a better reactivity and temperature rising time, including in cold-start operation. However, a rapid physical degradation accompanied by pressure peaks observed throughout testing of the 1-mm catalyst led to damage of the catalyst and apparition of fines, causing partial clogging of the bed.

The influence of diamond grain sizes on the tribological performance and ultimate loading capacity of polycrystalline diamond self-mated friction pairs under water lubricated condition

The influence of diamond grain sizes on the tribological performance and ultimate loading capacity of polycrystalline diamond self-mated friction pairs under water lubricated condition

Surface modification of Zr–Nb alloy by nanosecond pulse laser processing

The effect of nanosecond pulse laser processing of the Zr–1% Nb alloy surface of specimens in the annealed state and after their two-stage deformation treatment by abc-pressing and rolling has been investigated. The morphology of the modified surface of specimens is described using optical and scanning microscopy. Furthermore, the microrelief formed as a result of vaporization and melting of a thin layer of material subjected to laser processing is evaluated quantitatively. Durometric measurements were conducted to ascertain the hardness of the near-surface layer and the impact of laser-induced shock waves on its hardness. The electron backscattering diffraction (EBSD) analysis data were employed to describe the structure of the specimens in the near-surface layer. The influence of the initial grain size on the quality of the modified surface, as well as on the depth and hardening of the near-surface layers has been established.

Investigation of shear mechanical behaviors of geogrid-coral sand interfaces

Geogrid-reinforced coral sand (GRCS) effectively enhances the strength and stability of marine geo-structures in island and coastal areas. The complex interaction and underlying mechanism of the geogrid-coral sand interface potentially determine the mechanical properties of the GRCS. In this study, large-scale interfacial shear tests were carried out to investigate the mechanical behaviors of geogrid-coral sand interfaces under the coupled influence of grain size, geogrid properties, and stress level. Comparisons with siliceous sand indicate that the mechanical properties of the geogrid-coral sand interface are excellent but suffer from more complex influences originating from particle properties. The interfacial friction angle is more sensitive to grain size, whereas the pseudo cohesion is more sensitive to aperture properties. The shear interface shows a general evolution trend of “contraction-dilation-contraction”, with the maximum and final dilation becoming more prominent as the aperture size and stress level decrease. The increase in grain size, vertical stress and geogrid apertures induces a thicker interface with more particle crushing. Given the microscopic geogrid-coral sand interaction, the force characteristics of the aperture are further analyzed, and an equivalent additional stress calculation method is developed to quantitatively characterize the effects of grain size, geogrid properties, and stress level.

The Influence of Grain Size on the Abrasive Wear Resistance of Hardox 500 Steel

High-strength martensitic steels with boron are among the leading materials widely recognized for their exceptional resistance to abrasive wear. These steels exhibit some of the highest strength indices among bulk steels, a result of their specific chemical composition, thermomechanical rolling processes at the steel mill, and the use of pure, high-quality ores. With hardness values ranging from 400 to 650 HBW, they are ideal for demanding applications such as excavator buckets, plow blades, shafts, wear-resistant bars, and container liners. One critical microstructural property contributing to their high mechanical performance is the prior austenite grain size (PAG). A finer grain structure is associated with enhanced plasticity, and plastic deformation plays a significant role in abrasive wear mechanisms. However, this relationship between grain size and wear resistance is not well-documented in the literature, with few studies providing specific quantitative data. To address this gap, the authors conducted a study to examine the effect of prior austenite grain size on wear resistance when exposed to loose abrasive electrofused alumina no. 90. The findings indicate that applying targeted heat treatment can increase hardness by 58 Brinell units compared to the as-delivered condition. Moreover, as grain size increases from 18 µm to 130 µm, the relative abrasive wear resistance coefficient Kb decreases from 1.00 (for Hardox 500 steel in its as-delivered state) to 0.80 for austenitized material treated at 1200 °C.

The high burn-up structure evolution in polycrystalline UO2: Phase-field modeling investigation

Abstract Understanding the evolution of microstructure in nuclear fuels under high burn-up conditions is a critical concern aimed at extending fuel refueling cycles and enhancing nuclear reactor safety. In this study, a phase-field model has been proposed to examine the evolution of high burn-up structures in polycrystalline UO2. The formation and growth of recrystallized grains were initially investigated. It was demonstrated that recrystallization kinetics adhere to the KJMA equation, and recrystallization represents a process of free energy reduction. Subsequently, the microstructure evolution in UO2 was analyzed as burn-up increased. Gas bubbles acted as additional nucleation sites, thereby augmenting recrystallization kinetics, while the presence of recrystallized grains accelerated bubble growth by increasing the number of grain boundaries. The observed variations in recrystallization kinetics and porosity with burn-up closely align with experimental findings. Furthermore, the influence of grain size on microstructure evolution was deliberated upon. Larger grain sizes were found to decrease porosity and the occurrence of high burn-up structures.

Effects of Recovery and Phase Transformation on the Recrystallization Kinetics of Ti-6Al-4V During β-Processing

This work unifies the description of microstructure evolution during dynamic and static recrystallization of Ti-6Al-4V in a single model. The developed model incorporates the role of dislocation interactions on the phenomenological concepts of dynamic and static recovery, continuous dynamic and static recrystallization, nucleation rate, and grain growth. The β-grain elongation during hot compression and the role of the deformed prior β-grain size on the number of potential nucleation sites are considered to visualize the influence of the initial grain size before deformation on the kinetics of static recrystallization. The model is calibrated and validated with experimental data from Ti-6Al-4V samples thermomechanically treated in the β-domain. Finally, the model is implemented as subroutines into the commercial FEM-based software DEFORM™ 2D. The proposed model accurately predicts I) the flow behavior and grain refinement during supertransus deformation, II) the influence of initial grain size, temperature, and deformation rate on the static recrystallization kinetics, and III) the grain growth kinetics. Simulations of hot forming followed by isothermal heat treatment and continuous cooling show that the Zener drag effect due to the formation of the α-phase has a greater influence on the kinetics of β-recrystallization than the cooling rate itself.

Hydrodynamic and reaction kinetic responses of CaO/CaCO3 carbonation in bubbling fluidized bed reactors for thermochemical energy storage: Influence of CO2 mole fraction, grain size, and reactor dimensions

The CaO/CaCO3 thermochemical energy storage system offers a promising method for the efficient utilization of solar energy. However, the reactor design remains underdeveloped. In this study, the Eulerian-Eulerian two-fluid model is employed to systematically investigate the effects of CO2 mole fraction, particle size, and reactor dimensions on the carbonation process in a bubbling fluidized bed reactor. Increasing the CO2 mole fraction from 50 % to 80 % reduces the duration of the chemical-reaction-kinetics controlled stage from 118.5 s to 65.3 s, and the transition stage from 64.6 s to 36.7 s, with minimal impact on the final conversion rate. High CO2 concentrations cause insufficient bed fluidization and uneven local conversion rate distribution within the bed. As the grain size increases from 150 nm to 300 nm and 600 nm, the duration of the chemical-reaction-kinetics controlled stage decreases from 118.5 s to 104.0 s and 76.2 s, respectively. This causes the reaction to enter the transition phase earlier, ultimately leading to a reduction in the maximum conversion rate. Altering the height and width of the reactor does not significantly impact the conversion processes within the reactor. These findings provide valuable insights for the optimization and practical industrial application of efficient reactors.

Effect of diamond grain size on mechanical properties and cutting performance of PCD tool in milling of Cf/SiC composites

The polycrystalline diamond (PCD) tools have excellent cutting performance in machining composites. However, the tool wear mechanism of PCD tools in milling Cf/SiC composites remains unclear. There are few researches on the effect of diamond grain size on the cutting performance of PCD tools and material removal mechanism. In this paper, four PCD samples with different grain sizes were prepared under high-temperature and high-pressure condition. The microstructure, flexural strength, and cutting performance of PCD samples was tested. The wear mechanism of the tools was analyzed by observing the wear morphology of the front and rear cutting surfaces of the PCD tools. The influence of diamond grain size on the cutting performance of PCD tools was investigated in terms of tool life, surface roughness and material removal mechanism. The results indicated that the highest bending strength was found in the PCD sample with the grain size of 5 μm, as the diamond grain size increased, the bending strength of the PCD tool decreased. Tool failure was caused by fiber bundles and chip dust scratching the binder and diamond grains. In the same cutting distance, due to the difference in bonding between diamonds of different grain sizes. The 2 μm∼30 μm grain size of the PCD tool wear was the slowest, 5 μm grain size of the fastest PCD tool wear. As the grain size decreased, the machined surface quality of Cf/SiC composites improved. The fiber removal mechanisms employed the gradual transition from shear removal to bending removal as the grain size increased.

Improvement of Mechanical Properties and Corrosion Resistance of As‐Extruded Mg–2Zn–2Al–0.3Mn Alloy Through Y Addition

The microstructure of as‐extruded Mg–2Zn–2Al–0.3Mn–xY (0 ≤ x ≤ 5 wt%) alloys are investigated, revealing the influence of grain size and second‐phase particle size on the mechanical properties and corrosion resistance of alloys. Additionally, the alloy composition is optimized. In the results, it is indicated that all alloys undergo complete dynamic recrystallization. The average dynamic recrystallization grain size decreases, accompanied by the appearance of Al2Y and (Al, Zn)11Y3 particles whose contents and sizes increase as Y content increases. Therefore, the mechanical properties improve due to fine grain strengthening and fine particle dispersion strengthening, while corrosion resistance benefits also from the grain refinement at Y contents between 0 and 3 wt%. A rapid increase in size and number of larger second‐phase particles leads to a decrease in the alloys’ mechanical properties corrosion resistance, with excess addition of Y. Accordingly, an optimized Y addition is determined to be 3 wt% in this study.

Interlayer Friction Mechanism and Scale Effects in Ultra-Thin TA1 Titanium Alloy/Carbon Fiber-Reinforced Plastic Laminates

Fiber metal laminates (FMLs) are a novel lightweight composite material, predominantly utilized in the aerospace sector for large-scale components like skin panels and fuselages. However, research on FMLs in the microsystem domain remains limited. Additionally, they are influenced by scale effects, rendering macroscopic forming theories inadequate for microforming applications. The application of ultra-thin fiber metal laminates in the microsystem field is hindered by this constraint. This paper investigates the friction performance of ultra-thin TA1 titanium alloy/carbon fiber-reinforced plastic (CFRP) laminates at the microscale. The content of the epoxy resin used is 38.0 ± 3.0%. Friction tests on ultra-thin TA1/CFRP laminates were conducted based on the Striebeck friction theory model. The effects of factors such as the weaving method, ply angle, normal force, tensile speed, and temperature on friction performance are explored in the study. Furthermore, the influences of geometric scale and grain scale on friction performance are examined. Geometric scale effects indicate that an increase in laminate width leads to an increase in the friction coefficient. Grain-scale effects demonstrate that as grain size increases, the friction coefficient also increases, attributed to reduced grain boundaries, increased twinning, and increased surface roughness of the metal. Finally, surface morphology analysis of the metal and fiber after friction tests further confirms the influence of grain size on the friction coefficient. Through detailed experimental design, result analysis and graphical representation, this paper provides a scientific basis for understanding and predicting the friction behavior of ultra-thin TA1/CFRP laminates.

Influence of the grain size on the martensitic transformation and strain nanodomains in the Ti-Hf-Ni-Cu shape memory alloy

The martensitic transformation and strain nanodomain were studied in the Ti40.7Hf9.5Ni44.8Cu5 shape memory alloy, whose grain size varied from 130 μm to 160 nm. The largest average grain size (600 μm in length and 130 μm in diameter) was found in the CAST sample. The grains with the smallest size (160 nm) formed during the crystallisation of thin ribbons obtained by the melt spinning technique from the Ti40.7Hf9.5Ni44.8Cu5 ingot (labelled as RIBBON). The average grain size (16 μm) was observed in the sample subjected to high-pressure torsion and post-deformation annealing (labelled as HPT). It was found that the CAST and HPT samples included the NiTi-based matrix and the Ti2Ni-type precipitates, whereas the RIBBON sample contained the NiTi-based matrix only. Regardless of the grain size, all samples underwent the B2 ↔ B19’ transformation on cooling and heating. A decrease in grain diameter from 130 μm to 160 nm decreased the transformation temperatures by more than 100 °C but did not affect the sequence of the transformation. The strain nanodomains formed in all samples on cooling prior to the forward martensitic transformation. The smaller the grain size, the larger the temperature range of the strain nanodomain existence. On heating of HPT and RIBBON samples, the B19 phase transformed to the B2 phase with strain nanodomains, which disappeared only on heating over 120 °C. The influence of grain size on the martensitic transformation and strain nanodomains was analysed from the thermodynamics approach.

Study on the Effect of Coal Grain Size on the Morphology of Soot Generated During Combustion

This study performed an experimental exploration to analyze the influence of different grain sizes of coal on the nanostructure and morphological parameters of soot generated during combustion. Initially, primary and mature soot samples were gained from the combustion flames of two different grain sizes of coal (less than 150 μm, named sample #1, and 6–8 mm, named sample #2) by using thermophoresis sampling technology. Subsequently, the transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to investigate and analyze the soot samples, with the aim of obtaining their morphological parameters and nanostructure characteristics. The TEM images indicate that the nascent soot produced during the flame formed by small-sized coal is relatively uniform, with individual particles 8–14 nm in size. The grain size of the nascent soot produced by large-sized coal is much larger, within a wide range of 50–350 nm. Additionally, the nanostructures of the nascent soot particles produced by samples #1 and #2 mainly consist of upright parallel crystal stripes. The crystal stripes of the soot particles formed by sample #1 have obvious microcrystalline structures, whereas only a small amount of microcrystalline structure is found at the edge of sample #2. Compared with sample #2, the soot formed during the combustion of sample #1 exhibits a denser crystalline structure. The SEM results indicate that the mature soot agglomerates formed in sample #2 are larger and more in quantity compared to sample #1. Furthermore, the mature soot agglomerates formed in sample #2 have a stronger coagulation performance and a more compact structure than that formed in sample #1.

Enhancement of the mechanical properties of semi-stationary bobbin tool friction stir welded joints in AA2219 through post-weld heat treatment

This research investigates the enhancement of AA2219 joints formed by semi-stationary bobbin tool friction stir welding (SSBT-FSW) through post-weld heat treatments. Although solid-state processes such as SSBT-FSW are able to produce superior welds without common defects seen in conventional fusion welding of aluminum alloys of the 2XXX series, the thermal cycle in SSBT-FSW can deteriorate mechanical properties by causing precipitate dissolution and over-aging. The research proposes using a heat treatment sequence to induce solubilization and re-recipitation of precipitates in a more favorable distribution, re-activating the precipitation-hardening. Since abnormal grain growth is very difficult to avoid during heat treatments of welded samples, the analysis focuses on the evolution of the microstructure during solution heat treatment and on the influence of grain size, texture, and precipitate distribution on grain growth. The origin and evolution of the grain growth during solution heat treatment have been observed. Hardness measurements and tensile tests show that post-weld heat treatments can effectively restore the mechanical properties of the joints to the levels of those of the base material. Understanding the relationships between microstructure, abnormal grain growth and mechanical behavior of the joints aids the optimization of the SSBT-FSW process for broader industrial application, especially in the aerospace industry, where high-performance aluminum welded structures are critical.

Influence of grain size on strain-induced phase transformation in a CrCoNi multi-principal element alloy

A Cr40Co40Ni20 (at.%) alloy with different grain/crystallite sizes was analyzed through in-situ synchrotron X-ray diffraction during tensile testing. The FCC starting structure underwent a partial strain-induced transformation to HCP (TRIP effect) and the percent transformed was measured throughout the deformation. The critical stress required to form a certain HCP fraction was shown to follow a Hall-Petch relation (σTRIP = σTRIP,0+ kTRIPd-0.5), with the Hall-Petch slope being approximately the same for yield stress and TRIP effect (ky ≈ kTRIP). Furthermore, this work developed a Hall-Petch-based model that correlates the applied stress, the transformed phase fraction, and the initial FCC grain/crystallite size. It predicts the stress required to form a certain HCP fraction, or the fraction formed when a certain stress is applied, for different grain/crystallite sizes. We also proposed a mechanism to explain the grain/crystallite size dependence of the TRIP effect and discuss how the TRIP effect and its early activation in the Cr40Co40Ni20 alloy provide high work-hardening capacity, which improves ductility and toughness. Here, a refined FCC grain size (d = 1.3; c = 0.7 μm) was shown to increase the yield stress by at least 100 % (417 → 834 MPa), compared to a coarser grain material (17; 6.8 μm), while maintaining a high ductility of 41 %. This work contributes to a better understanding of the deformation mechanisms, mainly the strain-induced phase transformation (TRIP), highlighting their impact and importance on mechanical properties.

Effect of grain size on mechanical properties and aging of yttria-stabilized tetragonal zirconia polycrystal fabricated by stereolithography-based additive manufacturing

The objective of this investigation was to comprehensively assess the impact of grain size on the mechanical properties and low-temperature degradation (LTD) of yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) fabricated by stereolithography-based additive manufacturing at the submicron scale. Four 3Y-TZP ceramics with high relative density (>98 %), ranging in grain size from 0.2 μm to 1 μm, were successfully prepared and validated for studying mechanical properties (including Vickers hardness, fracture toughness, and flexural strength) as well as LTD progression. This study elucidates the mechanical behavior of zirconia ceramics at the submicron scale, focusing on fracture micromechanisms and the grain size dependence of transformation toughening. Additionally, it examines the influence of grain size on the hydrothermal aging behavior of zirconia ceramics at the submicron scale using Raman spectroscopy.

Influence of grain size and orientation on the uneven precipitation in Al–Cu–Li alloys

The effects of grain size and orientation on the precipitation behavior of the T1 (Al2CuLi) phase in 2050 T8 sheets are quantitatively investigated using transmission Kikuchi diffraction (TKD) and transmission electron microscope (TEM). The results indicate that the T1 phase predominantly precipitates at high densities on the activated slip planes, results in a reduction of the precipitation strengthening effect. In grains of near the R-Cube orientation, the volume fraction of T1 phase within the sub-grains is approximately 12% higher than that in the recrystallized grains, while the contribution to strengthening effect through precipitation is comparable.

The Influence of As-Cast Grain Size on the Formation of Recrystallized Grains and the Related Mechanical Properties in Al-Zn-Mg-Cu-Based Alloy Sheets.

The influence of as-cast grain size on recrystallization and the related mechanical properties of Al-Zn-Mg-Cu-based alloys was investigated. Grain sizes ranging from 163 to 26 μm were achieved by adding Ti, Cr and Mn, and ZnO nano-particles, which acted as heterogeneous nucleation sites. A decrease in the as-cast grain size led to a corresponding reduction in the recrystallized grain size from 54 to 13 μm. Notably, as-cast grain sizes below 100 μm provided additional nucleation sites at grain boundaries, allowing for a reasonable prediction of recrystallized grain size. Finer grains also contributed to enhanced mechanical properties, with yield strength increasing as recrystallized grain size decreased without significant loss of elongation. Additional strengthening was observed due to η-precipitates at grain boundaries, further improving the properties of fine-grained sheets.

Ultralow thermal conductivity in Si–Ge nanograin mixtures: A cost-effective granular material for thermoelectric applications

This paper presents a theoretical study of the thermal conductivity of Si–Ge nanograin mixtures using a multiscale computational methodology based on solving the Boltzmann transport equation for phonons with first-principles techniques. A size-dependent correction factor is developed to account for the spatial dependence of the phonon distribution function on nanograin size, with parameters derived from the phonon properties of infinite Si and Ge crystals. This approach makes it possible to accurately calculate the thermal conductivity within a single nanograin, using force constants obtained from first-principles calculations. Thermal energy transport by phonons across grain boundaries is modeled by accounting for phonon transmission by two-phonon processes, weighting specular, and diffuse transmission for each phonon mode as a function of the root-mean-square roughness of the boundary relative to the phonon wavelength. The boundary thermal conductance model, previously validated against experimental data, is implemented using first-principles techniques. This approach excludes specular transmission for phonon modes with specific symmetries while ensuring conservation of the total number of modes in each symmetry class. The study examines the influence of grain size, nanograin mixture composition, temperature, and boundary asperities on the thermal conductivity of nanograin mixtures.