Effect Of Grain Size Research Articles

Synergistic effect of grain size and surface oxygen vacancies for enhanced photoresponse properties of nanocrystalline SnO2 films

The photoresponse properties of nanocrystalline tin dioxide (SnO2) thin films with different grain sizes were systematically studied for fabricating transparent oxide-based ultraviolet (UV) photodetector. SnO2 nanoparticles were synthesized using the coprecipitation method and calcination temperatures were varied (400 °C–800 °C) to prepare SnO2 particles of different grain sizes (∼8 nm–∼42 nm). Subsequently, thin films of SnO2 nanoparticles were deposited using the spin-coating technique to fabricate UV photodetectors. The optical transparency of SnO2 thin films was improved by 10 % with the increasing grain size of the sample, while the band gap of the films was found to vary from 3.718 eV to 3.761 eV. The responsivity (Rλ) and the external quantum efficiency (EQE) of SnO2 based photodetector were noticeably large (Rλ = 200 mA/W and EQE = 90 %) in the UV range for devices with the smallest grain sizes (∼8 nm). Moreover, the same device exhibited a much faster photoresponse time (∼2 s) and a large photo-to-dark current ratio (∼103). The structural and spectroscopic studies on the SnO2 thin films revealed that the microscopic parameters like grain size, grain boundary potential, and surface oxygen vacancies play significant roles in modulating the optical properties and photoresponse of the nanocrystalline SnO2 thin films.

Fatigue Crack Propagation Across the Multiple Length Scales of Technically Relevant Metallic Materials

The fundamentals of our understanding of fatigue crack propagation were formed more than 60 years ago by Paul C. Paris. Since then, the run toward new metallic materials and alloys with ever finer-grained microstructures has had a large impact on research. Along with enormous variation of the microstructural length scales (i.e., grain size), the essential parameters for the description of fatigue crack growth, such as the crack propagation rate and plastic zone size, also exhibit an immense change from the subnanometer to the micrometer regime. These enormous variations in the fatigue crack growth behavior's controlling parameters motivate this contribution. This article presents an overview of the effect of grain size, from the millimeter to the nanometer grain-size regime, on fatigue crack propagation of mainly ductile metals and alloys with an attempt to summarize the most important findings and underlying physical phenomena, including with respect to selected materials such as pure iron, nickel, and austenitic and pearlitic steel.

Effect of grain size on irradiation-induced bubble evolution in high burn-up UO2: A phase-field study

Due to economic reasons, uranium dioxide (UO2) ceramic fuel needs to operate under high burn-up conditions. The high burn-up structure (HBS) and micrometric irradiation-induced bubbles within it cause safety issues for the fuel. In this study, a phase-field model was developed to simulate the evolution of fission bubbles under high burn-up conditions. This model simultaneously couples the evolution of recrystallized grains and bubbles through explicit nucleation methods. By simulating the development of HBS in polycrystalline UO2, it was indicated that the microstructure is consistent with experimental observation. The variation of porosity was divided into three stages and found to be in good agreement with experimental data. Additionally, the HBS fraction was compared with experimental measurements to validate this HBS model. Furthermore, the effect of recrystallization on bubble evolution was investigated using the validated model. It was found that recrystallization accelerated bubble evolution by increasing GB area. In addition, the influence of grain size on bubble evolution was studied by constructing initial structures with different grain sizes. Results showed that both the development of recrystallization and the decrease in grain size enhance bubble evolution, but the enhancement becomes smaller as the grain size decreases.

Effect of TiC grain size on corrosion behaviors of Ti-Si-C nanocomposite coatings fabricated by heterogeneous targets high-power impulse magnetron sputtering

Ti-Si-C coatings with different carbon contents were prepared on SS316L substrates by heterogeneous targets high-power impulse magnetron sputtering with a repetitive C and TiSi deposition. Various tests were employed to analyze the microstructure, anti-corrosion properties in a simulated proton exchange membrane fuel cells (PEMFC) environment and interfacial conductivity of the coatings. Results indicated that the Ti-Si-C coating possessed a typical nanocomposite structure of TiC nanocrystals embedded in amorphous carbon matrix. With the increase of the carbon content, the grain size of TiC nanocrystals was reduced gradually. Electrochemical measurements revealed that a proper decrease of TiC grain size led to an enhanced corrosion resistance of the as-deposited coating. The smallest interfacial contact resistance and corrosion rate of the Ti-Si-C coating in the simulated PEMFC solution reached 5.07 mΩ cm2 and 5.93E-07 A/cm2, respectively. This improvement could be attributed to the formation of a dense and continuous passivation layer composed of Ti2O3 and SiO2 on the top surface of the coating.

Numerical investigation of grain size effect on velocity-skewed oscillatory sheet flow

Wave-induced sheet flow leads to intense sediment transport. Fine sand and medium/coarse sand exhibit opposite directions of net sediment transport under velocity-skewed oscillatory sheet flows. A newly developed two-phase mixture model is employed to simulate the sediment transport under these conditions. The model accounts for particle stress, two-phase momentum exchange, and turbulence modulation. The effects of grain size on flow characteristics and sediment transport are primarily investigated. The model effectively reproduces the spatial and temporal distributions of two-phase velocities and sediment concentration as well as the periodic distribution of erosion depth. Comparisons between configurations with medium and fine sand demonstrate that the grain size impacts sediment transport in two main ways. First, the grain size influences the periodic variations in erosion depth and the quantity of suspended sediment. A decrease in the grain size increases the phase residual and phase lag, enhancing offshore sediment transport. Second, suspended sediments modulate the flow dynamics within the oscillatory boundary layer. Through the mobile bed effect and density stratification, the grain size affects two-phase velocities, turbulence, and net sediment transport.

The effect of diamond grain size on the formability and mechanical property of 3D-printed diamond tool

Because of the flexibility of structure design and material design, 3D-printed metal-bonded diamond tool is expected to be the next generation of diamond tools. In this paper, the selective laser melting process is utilized to fabricate the metal-bonded diamond tool based on the mixed powders consisted of AlSi10Mg powder and diamond powder. Relative density, material characterization and mechanical property are measured to figure out the effect of diamond grain size on the formability and property of 3D-printed diamond tool with diamond grain size from 200 mesh to 500 mesh. The results suggest that, when the diamond volume fraction stays the same, with the diamond grain size decreasing, the relative density and main mechanical properties descend due to the increment of defects. Furthermore, the 3D-printed diamond tool with evenly distributed and firmly embedded diamond abrasives can be fabricated and corresponding mechanical properties can meet the requirement of diamond tool.

Effects of grain size and seawater salinity on magnesium hydroxide dissolution and secondary calcium carbonate precipitation kinetics: implications for ocean alkalinity enhancement

Abstract. Understanding the impacts that mineral grain size and seawater salinity have on magnesium hydroxide (Mg(OH)2) dissolution and secondary calcium carbonate (CaCO3) precipitation is critical for the success of ocean alkalinity enhancement. We tested Mg(OH)2 dissolution kinetics in seawater using three Mg(OH)2 grain sizes (<63, 63–180 and >180 µm) at three salinities (∼36, ∼28 and ∼20). While Mg(OH)2 dissolution occurred more quickly the smaller the grain size, salinity did not significantly impact measured rates. Our results also demonstrate that grain size can impact secondary CaCO3 precipitation, suggesting that an optimum grain size exists for ocean alkalinity enhancement (OAE) using solid Mg(OH)2. Of the three grain sizes tested, the medium grain size (63–180 µm) was optimal in terms of delaying secondary CaCO3 precipitation. We hypothesise that in the lowest-grain-size experiments, the higher surface area provided numerous CaCO3 precipitation nuclei, while the slower dissolution of bigger grain sizes maintained a higher alkalinity and pH at the surface of particles, increasing CaCO3 precipitation rates and making them observable much more quickly than for the intermediate grain size. Salinity also played a role in CaCO3 precipitation, where the decrease in magnesium (Mg) allowed secondary precipitation to occur more quickly, similar in effect size to another known inhibitor, i.e. dissolved organic carbon (DOC). In summary, our results suggest that OAE efficiency as influenced by CaCO3 precipitation depends not only on seawater composition but also on the physical properties of the alkaline feedstock used.

Effects of rotational speed of the classifying wheel during jet milling on magnetic properties and thermal stability of sintered Nd-Fe-B magnets

Sintered Nd-Fe-B magnets with different grain sizes are prepared by adjusting rotational speed of the classifying wheel during the jet milling process. The microstructures of the magnets, the element contents of the magnets, the relationship between powder particle size and grain size and the magnetic properties of the magnets are studied by X-ray diffracton (XRD), scanning electron microscopy (SEM), optical microscopy (OM), electron backscattered diffraction (EBSD), inductively coupled plasma (ICP) and permanent magnet tester. The effect of grain size on thermal stability is characterized by the temperature coefficient of coercivity from room temperature to working temperature and the irreversible magnetic flux loss of the magnet at high temperature. The results show that the particle size of the alloy powder decreases with the increase of the rotational speed of the classifying wheel. When the alloy powder is formed and sintered, it is found that the grain size of the prepared magnet decreases with the decrease of the particle size of the alloy powder. The finer the grain size of the magnet, the clearer the grain boundary. As the grain size of the magnet decreases, the coercivity of the magnet increases, the remanence of the magnet decreases slowly and the thermal stability of the magnet becomes better. For the magnet with a rotational speed of the classifying wheel of 4900 r/min, the average grain size of the magnet is 4.70 μm, the coercivity (Hcj) is 15.47 kOe, and the remanence (Br) is14.09 kGs. At a temperature of 80 °C, the coercivity temperature coefficient of the magnet reaches −0.745 %/°C, and the irreversible loss of magnetic flux hirr is 16.49 %. In addition, the magnet prepared by the tail material produced a large number of voids and pores due to the high oxygen content. Tail material is not good enough in terms of magnetic property as well as thermal stability.

The effect of grain size and anomalous shape on low cycle fatigue of nickel-based superalloy at elevated temperature

The effect of grain size and shape on low cycle fatigue of a nickel-based superalloy at elevated temperature was investigated. Fatigue testing was performed using GH4742 specimens having fine, coarse, and irregular grains. The fine-grained material exhibits a transition strain separating the fatigue life diagram into two regimes with distinct slopes while the other two do not. A piecewise log-linear model was proposed to incorporate the transition strain, yielding more accurate predictions. Crack initiation modes and cyclic deformations at half-life were investigated to explain the observed difference and fatigue behavior characteristics of the three grain types.

Enhanced mechanical properties and electromagnetic interference shielding effectiveness in Mg‐6Zn‐1Y‐1La‐0.5Zr alloy sheet by hot deformation

Striking a balance between the mechanical properties and electromagnetic interference shielding effectiveness (EMI SE) of Mg alloys stands as a critical concern within the realm of electronics and communications. This study endeavors to optimize the mechanical properties and EMI SE of Mg alloy sheets through a combination of extrusion and rolling (E-R). OM, SEM, XRD, EBSD, and TEM obtained the microstructures of Mg‐6Zn‐1Y‐1La‐0.5Zr alloys under extrusion and different rolling strain treatments, and the effects of the microstructures on the mechanical properties and EMI SE were revealed. The microstructure of the as-extruded Mg‐6Zn‐1Y‐1La‐0.5Zr (abbreviated as ZKL611K) alloy exhibited a distinct bimodal microstructure, with refined dynamically recrystallized (DRXed) grains surrounding coarse unDRXed regions. Subsequent rolling treatments induced a decrease in the aspect ratio of the unDRXed regions, a rapid reduction of DRXed grains, and the accumulation of dislocations within the as-rolled alloy. Statistical analysis of mechanical properties and EMI SE revealed that an optimal balance in the sheets subjected to “extrusion + 37 % rolling reduction”, yield strength (YS) of 319 MPa, ultimate tensile strength (UTS) of 375 MPa, and elongation of 12.3 %. Furthermore, the EMI SE ranged from 81 dB to 114 dB within the frequency range of 30–1500 MHz. However, further increments in rolling reduction adversely affected mechanical properties while improving EMI SE. The observed enhancement in mechanical properties can be primarily attributed to the synergistic effects of grain size, second phase, dislocations, low-angle grain boundaries (LAGBs), and texture. Meanwhile, the improved EMI SE can be mainly attributed to the diffuse distribution of the second phase at multiple scales and the modulation of the texture through E-R treatments.

Experimental sticking coefficients of CO and N_2 on sub-micrometric cosmic grain analogs

Measuring the sticking coefficient of molecules pertinent to astrochemistry - such as CO - on substrates that mimic interstellar dust grains is crucial for the comprehensive understanding of gas-grain chemical processes. Although astrochemical models assume a sticking coefficient of 1, recent laboratory experiments on H2O and CO2 have revealed significantly lower values when measured on small grain analogs. As the effect of grain size on molecular adsorption has been largely ignored to date, further experiments are needed to determine the accretion rates of species known to freeze out on dust grains. Our aim is to determine the sticking coefficients of CO and N2 on sub-micrometric silicate and carbon grains. By quantifying realistic sticking coefficients on these dust grain analogs, we can improve the accuracy of astrochemists' predictions of molecular abundances as affected by gas-grain interactions. The molecules of interest were added to various substrates at 10 K in an ultra-high vacuum. The amount of adsorbate that stuck to the substrate was quantified using X-ray photoelectron spectroscopy. These quantities were compared to a reference with a sticking coefficient of 1, allowing the deduction of the sticking coefficient for each substrate. The average sticking coefficients of CO and N2 on grain analogs are 0.17 for CO and 0.14 for N2 on olivine powder, and 0.05 for CO and 0.07 on N2 on soot, instead of the presumed 1. This is in line with the low values previously reported for H2O and CO2 These laboratory results indicate that CO and N2 in addition to H2O and CO2 also exhibit a low sticking coefficient on dust grain analogs. It is thus necessary to reconsider the interactions between gaseous species and dust particles as a low-efficiency process. This reduction in accretion and reaction rates has important implications for how we understand astrochemistry.

Achieving superior strength-ductility synergy and enhanced corrosion resistance in a novel medium-entropy alloy via grain refinement strategy

The effect of grain size on mechanical properties and corrosion resistance of Ni62Cr10V28 MEA was investigated. The findings indicated that grain refinement significantly enhanced the corrosion resistance of the investigated alloys, attributed to the distinctive characteristics of grain boundaries and the fast formation rate of passive film. Additionally, the investigated alloys demonstrated a yield strength ranging from 518.7 MPa to 714.2 MPa, accompanied by an elongation ranging from 46.29 % to 50.48 %, thereby attaining a superior strength-ductility balance. Overall, grain refinement demonstrates a favorable synergistic effect on both mechanical properties and corrosion resistance.

Effect of Grain Size on the Uniaxial Compressive Strength of Ice Forming with Different Wind Speeds in a Cold Laboratory

This study investigated the uniaxial compressive strength of distilled water ice prepared in a low-temperature laboratory at −30 °C at varying wind speeds of 0 m/s, 1 m/s, 2 m/s, 4 m/s, 6 m/s, and 8 m/s. The crystal structure and grain size of the ice were measured. The results indicated that, during the ice forming period, the higher the wind speed, the lower the grain size. Uniaxial compression tests were conducted parallel to the ice crystal long axis direction within a strain rate range of 10−6 s−1 to 10−2 s−1. The experimental temperature was controlled at −10 °C. Stress–strain curves were generated, elucidating the mechanical properties and failure modes of the ice. The results suggest that the uniaxial compressive strength of ice is related to the strain rate by a power–law function and shows a linear correlation with −1/2 power of grain size. The results explain the physical fact that the strength of ice is higher when the ice is formed in low-temperature and high-wind-speed environments. Additionally, this highlights how wind speed influences ice strength by controlling grain size during ice forming.

Microstructural evolution and mechanical behavior of activated tungsten inert gas welded joint between P91 steel and Incoloy 800HT

This study examines the welded joint between P91 steel and Incoloy 800HT using the activated tungsten inert gas (A-TIG) welding process. The focus is on analyzing the microstructure and evaluating the mechanical properties of joints made with different compositions of activating flux. Owing to the reversal of the Marangoni effect in which the conventional direction of molten metal flow in the weld pool is reversed due to the application of oxide-based fluxes, a complete depth of penetration of 8 mm was successfully achieved. Conducting mechanical tests, such as microhardness, tensile, and Charpy impact toughness tests, elucidates the behavior of the welded specimens under different loading conditions. The findings highlight the effects of grain size, dislocations, and the evolution of fine-sized precipitates in the high-temperature matrix. This study highlights the importance of choosing suitable flux compositions to achieve consistent penetration and dilution in the base metals. Insights into different failure modes and the influence of temperature on the tensile strength were evaluated. Beneficial mechanical properties of the joints (meeting the criteria of ISO and ASTM standards) were found: ultimate tensile strength of 585 ± 5 MPa, elongation 38 ± 2%, impact toughness of 96 ± 5 J, and maximum microhardness of 345 ± 5 HV.

Understanding the effect of microstructure on the failure behavior of additively manufactured Al2O3 ceramics: 3D micromechanical modeling

Additively manufactured (AM) ceramics are gaining popularity due to improved flexibility in the design of customized structures. Microstructure-based finite element (FE) models were developed to study the strain-rate-dependent failure behavior of AM Al2O3 ceramics under uniaxial compression. Upon validation with experimental data, the model was leveraged to quantify the history of intergranular and transgranular failure mechanisms across microstructures. It was revealed that the intergranular mechanism plays a key role in the material strength across strain rates. Crystallographic orientations were found to remarkably decrease the material strength due to the earlier initiation and faster growth of the intergranular mechanism. The increase in porosity was found to amplify the transgranular mechanism resulting from a higher number of pores acting as crack nucleation sites, decreasing the material strength regardless of strain rate. The model reflected the existence of a threshold for grain boundary strength, beyond which further enhancements yield marginal improvements in material strength. Additionally, the effect of grain size on the initiation and evolution of failure mechanisms was studied and the corresponding limitations of the model were discussed. The current work correlates the microstructure of the material to its macroscale response through micromechanical models, informing the design of better-performing AM Al2O3 ceramics.

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.

Substitution modification mechanism of YIG ferrite with a high spin-wave linewidth via fast relaxation Dy3+ ion doping and sintering modulation

YIG ferrites are often used as nonreciprocal materials in microwave ferrite devices because of their low microwave magnetic and dielectric losses. To comply with the trend of planarization and integration of microwave systems, YIG ferrites are required to withstand higher powers. In this study, we investigated the variation in material microwave properties with material composition and microstructure. The experimental results show that doping the material with high-relaxation ions Dy3+ combined with modulating the sintering holding time can effectively improve the material’s high-power microwave signal withstanding capability, and YIG ferrite with a spin-wave line width of 18.7 Oe is obtained. In addition, when the average grain size of the material is controlled within 5 μm, the effect of the average grain size on the spin-wave linewidth is more noticeable than that of Dy3+ substitution.

Effect of prior austenite grain size on austenite reversion, bainite transformation and mechanical properties of Fe-2Mn-0.2C steel

To elucidate the response of austenite reversion and subsequent bainite transformation behavior to the prior austenite grain (PAG) size, the transformation kinetics and amount of reverted austenite in the intercritical region, the subsequent bainite transformation kinetics, and the tensile properties were investigated by dilatometers, scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy, and the mechanical tests. The results show that, when annealed at 730 °C, fine-grained specimens exhibit faster reverted austenite transformation rate than coarse-grained specimens due to the presence of more PAG boundaries. As the intercritical temperature rises to 760 °C, more intragranular globular austenite forms in the coarse-grained specimen, which accelerates the reverted austenite transformation rate. Compared to fine-grained specimens, coarse-grained specimens exhibit faster bainite transformation and higher amount of bainitic ferrite. The microstructure after austempering consists of intercritical ferrite, bainitic ferrite, RA and fresh martensite. With increasing the austempering time, more bainitic ferrite is formed and the amount of RA and fresh martensite decreases. With increasing the austempering time, the increase in the amount of bainitic ferrite leads to an increase in the yield strength, while the decrease in the amount of RA leads to a decrease in the elongation. Moreover, compared with coarse-grained specimens, the finer microstructure in fine-grained specimens improves yield and tensile strengths, while higher amount of RA contributes to larger uniform and total elongations.

The effect of prior austenite grain size on crystallography and variant selection in carbide-free nano-structured bainite

Prior austenite grain size (PAGS) significantly affects the microstructure and in turn the mechanical properties of nano-structured bainite. In this study, information about crystallographic variants/blocks as well as packets has been extracted using electron backscattered diffraction (EBSD) technique for two blocks of nano-baintic steels with different PAGS obtained by austenitization at two different temperatures of 900°C and 1000°C respectively. However, the bainitic fraction has been maintained to be similar by choosing the same isothermal temperature of 250°C for transformation to bainite. The child-parent orientation relationship (OR) was determined to be close to Kurdjumov-Sachs (K-S) using EBSD for larger PAGS specimen while smaller PAGS specimen displayed closeness to K-S OR predominantly and Nishiyama-Wassermann (N-W) OR in some regions. It was observed that a higher PAGS leads to finer bainitic lath thickness, packet size and block width size. Stricter variant selection was found in smaller PAGS sample even though variant pairing was observed between variants of higher misorientation. This hints towards small number of nucleation sites for a grain and space constraint, rather than the tendency for pairing as the reason for selection.

Effect of grain size and cobalt content on machining performance during milling tungsten carbide with PCD tool

Tungsten carbide has been extensively utilized in the manufacturing field due to its exceptional properties. However, traditional methods such as grinding or electric discharge machining often result in a low material removal rate and inevitable surface defects, making tungsten carbide one of the most challenging materials to machine. Milling has emerged as a promising alternative for machining tungsten carbide. However, the milling of tungsten carbide has not been widely applied in the industry due to a lack of comprehensive understanding regarding the milling performance of different tungsten carbides under various conditions. In this paper, a polycrystalline diamond (PCD) tool was used in the milling of tungsten carbides to investigate the effects of tool grain size, workpiece Co content, and WC grain size on tool wear and machining surface quality. It was found that PCD tools with larger grain sizes exhibited higher wear resistance. Additionally, excessive Co content in the workpiece and large WC grain size increased tool wear and degraded the quality of the machined surface. The primary types of tool wear observed in the milling of WC-Co included adhesive wear, abrasive wear, phase change wear, and oxidation wear.