Samples Of Different Grain Sizes Research Articles

The effect of grain size and rolling reduction on microstructure evolution and annealing hardening response of a Mg-3Gd alloy

Mg-3Gd (wt.%) samples with different initial grain sizes were prepared to evaluate the grain size effect on microstructural evolution during cold rolling and subsequent annealing hardening response. The deformation behavior and mechanical response of the as-rolled and annealed samples were systematically investigated by a combination of electron microscopy and microhardness characterization. The results show that the twinning activities were highly suppressed in the fine-grained samples during rolling. Upon increasing the rolling reduction to 40%, ultra-fine grain structures with a volume fraction of ∼28% were formed due to the activation of multiple slip systems. Conversely, twinning dominated the early stages of deformation in the coarse-grained samples. After a 10% rolling reduction, numerous twins with a volume fraction of ∼23% were formed. Further increasing the rolling reduction to 40%, high-density dislocations were activated and twin structures with a volume fraction of ∼36% were formed. The annealing hardening response of deformed samples was effectively enhanced compared to that of the non-deformed samples, which was attributed to the enhanced Gd segregation along grain boundaries, twin boundaries and dislocation cores. Moreover, the grain size and rolling reduction were found to affect the microstructure evolution during annealing, resulting in a notable difference in the annealing hardening response of Mg-3Gd alloy between samples of different grain sizes deformed to different strains. These findings highlight the crucial importance of microstructural and processing parameters in the design of high-strength, cost-effective Mg alloys.

Relationship between Induced Polarization Relaxation Time and Hydraulic Characteristics of Water-Bearing Sand

The induced polarization method has become a popular method for evaluating formation permeability characteristics in recent years because of its sensitivity to water and water-bearing porous media. In particular, the induced polarization relaxation time can reflect the macroscopic characteristics of the porous media of rock and soil. Therefore, in order to study the relationship between relaxation time and permeability, eight quartz sand samples of different grain sizes were used to simulate water-bearing sand layers under different geological conditions, and the induced polarization experiment and the Darcy seepage experiment were carried out on the same sand sample. The experimental results show that relaxation time and permeability are closely correlated with the grain size of quartz sand samples. According to the experimental data, the power function equation is a better fit for describing the relationship between permeability and relaxation time. It is worth noting that the equations obtained are only empirical equations for quartz sand samples, and they may not be applicable to all geological conditions.

Glacial Catchment Erosion From Detrital Zircon (U‐Th)/He Thermochronology: Patagonian Andes

AbstractAlpine glacial erosion exerts a first‐order control on mountain topography and sediment production, but its mechanisms are poorly understood. Observational data capable of testing glacial erosion and transport laws in glacial models are mostly lacking. New insights, however, can be gained from detrital tracer thermochronology. Detrital tracer thermochronology works on the premise that thermochronometer bedrock ages vary systematically with elevation, and that detrital downstream samples can be used to infer the source elevation sectors of sediments. We analyze six new detrital samples of different grain sizes (sand and pebbles) from glacial deposits and the modern river channel integrated with data from 18 previously analyzed bedrock samples from an elevation transect in the Leones Valley, Northern Patagonian Icefield, Chile (46.7°S). We present 622 new detrital zircon (U‐Th)/He (ZHe) single‐grain analyses and 22 new bedrock ZHe analyses for two of the bedrock samples to determine age reproducibility. Results suggest that glacial erosion was focused at and below the Last Glacial Maximum and neoglacial equilibrium line altitudes, supporting previous modeling studies. Furthermore, grain age distributions from different grain sizes (sand, pebbles) might indicate differences in erosion mechanisms, including mass movements at steep glacial valley walls. Finally, our results highlight complications and opportunities in assessing glacigenic environments, such as dynamics of sediment production, transport, transient storage, and final deposition, that arise from settings with large glacio‐fluvial catchments.

Tensile strength and fracture mechanics of two-dimensional nanocrystalline silicon carbide

Two-dimensional Silicon Carbide (SiC) has opened the route to a cornucopia of advanced functionalities in the realm of quantum condensed matter. It holds great promise for highly efficient nanoelectronic, optoelectronic, renewable energy, and spintronic applications thanks to the confluence of a wide spectrum of mesmerizing physical properties like a wide direct bandgap with high exciton binding energy, robust spin–orbit-coupling, excellent photoluminescence, suitable mechanical strength, and thermodynamic stability. Nonetheless, it is still a daunting challenge to incorporate SiC in functional systems since extensive analyses of the mechanical properties, and fracture mechanism of nanocrystalline (NC)-SiC is still obscure. In this light, this work is an attempt to report detailed information concerning the room-temperature tensile mechanical properties and fracture phenomena of NC-SiC executing Molecular Dynamics (MD) simulations. In particular, effects of grain size on the stress–strain profile, fracture strength, fracture strain, and Young’s modulus of the NC-SiC have been thoroughly investigated. It has been found that the strength as a function of grain size can be characterized by the inverse pseudo Hall-Petch relation. Increasing grain size brings about more elasticity in the structure, albeit at the price of fracture strain. The NC-SiC encounters a substantial degradation in mechanical properties relative to its single-crystal counterpart. Afterward, we performed an exhaustive fracture analysis on two NC-SiC samples of different grain sizes. The single-crystal SiC can endure more tensile strain before rupture compared to that of the NC-SiC. At last, the nanosheet exhibits more immunity to fracture with decreasing grain size. This study would lay the groundwork for NC-SiC to be successfully realized in functional systems as well as serving as a solid roadmap for engineering the mechanical properties of nanocrystalline materials.

Application of spectral signature to analyze quality of magnesite ore mineral deposits and altered rocks of Salem, India

The developers of remote sensing and an advancement of imaging spectroscopy have provided an opportunity to extract compositional information of mineral mixtures. The geochemistry and mineralogical studies support ethical hold on spectral compositional studies of the ultramafic complex. The Salem ultramafic complex region covered by peridotite, dunite, and magnesite ore and surrounded by country rocks like hornblende biotite gneiss and charnockite. The rock samples include peridotite, dunites, metagabbro, and different kinds of magnesite ore minerals collected from the magnesite mines sections and outcrops exposure of reflectance spectral studies, geochemical analysis, and petrographical studies. Spectral measurements were carried out under 350–2500 nm spectral range from whole rock as well as powdered samples of different grain sizes using ASD Spectroradiometer. In the spectral analysis, the intensity of the carbonate bands assumed as fewer than three spectral ranges at 1900 nm, 2300 nm, and 2450 nm bandwidth and band depth based on absorbing characters and quality. The common absorption bands for dunites are 640 nm, 1050 nm, 1392 nm, 1910 nm, 2325 nm, and 2388 nm. In the shorter wavelength region, OH/Mn3+, OH/Fe2+, Mg-OH vibration and carbonate absorptions indicate the presence of ferric iron, olivine, and pyroxene overlapping spectra. Assessing the proportions of composition of rocks and ore minerals based on the spectral signature is a challenging task due to the minerals that exist in the form of intimate mixtures and variations. A thin section study reveals the presence of the major minerals in the rocks and the characteristics of ore minerals. The XRF geochemistry exposes major oxides and determines correlation of the geochemical elements using cluster and PCA analysis.

Single-step, high pressure, and two-step spark plasma sintering of UO2 nanopowders

Three different spark plasma sintering (SPS) treatments were applied to highly sinteractive, near-stoichiometric UO2.04 nanocrystalline (5 nm) powders produced by U(IV) oxalate hydrothermal decomposition at 170 °C. The sintering conditions for reaching 95 % theoretical density (TD) in regular SPS, high pressure SPS (HP-SPS), and, for the first time, two-step SPS (2S-SPS), were determined. Densification to 95 % TD was achieved at 1000 °C in regular SPS (70 MPa applied pressure), 660 °C in HP-SPS (500 MPa), and 650−550 °C in 2S-SPS (70 MPa). With the goal of minimising the grain growth during densification, the sintering treatments were optimised to favour densification over coarsening, and the final microstructures thus obtained are compared. Equally dense UO2 samples of different grain sizes, ranging from 3.08 μm to 163 nm, were produced. Room-temperature oxidation of the powders could not be avoided due to their nanometric dimensions, and a final annealing treatment was designed to reduce hyperstoichiometric samples to UO2.00.

Effect of Grain Size on the Microstructure and Strain Hardening Behavior of Solution Heat-Treated Low-C High-Mn Steel.

The low-carbon high-Mn austenitic steel microalloyed with titanium was investigated in this work. The steel was solution heat-treated at different temperatures in a range from 900 to 1200 °C. The aim was to receive a different grain size before the static tensile test performed at room temperature. The samples of different grain sizes showed the different strain hardening behavior and resulting mechanical properties. The size of grain diameter below 19 μm was stable up to 1000 °C. Above this temperature, the very enhanced grain growth took place with the grain diameter higher than 220 μm at 1200 °C. This huge grain size at the highest temperature resulted in the premature failure of the sample showing the lowest strength properties at the same time. Correlations between the grain size, the major strengthening mechanism, and fracture behavior were addressed. The relationships were assessed based on microstructural investigations and fractography tests performed for the deformed samples. The best combination of strength and ductility was found for the samples treated at 1000–1100 °C.

大兴安岭北段阿里河地区1:5万土壤地球化学不同粒级样品对比研究

大兴安岭北段阿里河地区1:5万土壤地球化学不同粒级样品对比研究

Bleaching studies on Al-hole ([AlO4/h]0) electron spin resonance (ESR) signal in sedimentary quartz

Electron spin resonance (ESR) dating of sediments using quartz is most commonly used for older sediments (>100 ka), since large residuals render the ESR signal unsuitable for dating young sediments. The multiple-centre approach (utilising both Ti and [AlO4/h]0 signals) is usually used to test the resetting of the signals used for ESR dating. Here we work towards a better understanding of, and correction for, the residual signal in ESR samples of sedimentary quartz. We undertook multiple-centre ESR measurements using quartz [AlO4/h]0 and Ti signals on young aeolian samples of different grain sizes which have been independently dated using optically stimulated luminescence (OSL). Our results demonstrate that [AlO4/h]0 signal yields residuals indicating equivalent doses of about 500 Gy, substantially older than expected for the known OSL equivalent doses in the range of 8–37 Gy. The decay of [AlO4/h]0 signal as function of bleaching time can be represented by an exponential function. We investigate the dependence of the residual magnitude of the ESR signal as a function of the previous given dose and observe an exponential increase in the residual signal with dose. Such observations are consistent with the results of luminescence process modelling conducted for a model comprising two luminescence centres and several traps, one of which is a so-called deep disconnected trap that cannot be emptied during optical stimulation. We propose that bleaching occurs through an electron-hole recombination process with electrons released from optically sensitive traps. In addition to our new insights into the bleaching mechanisms of the [AlO4/h]0 ESR signal, we discuss the implications for the procedures used for performing residual dose corrections in ESR dating. We recommend that modern analogues be used in addition to laboratory-bleached samples when performing residual dose corrections.

Determination of distribution coefficient of uranium from physical and chemical properties of soil.

Uranium is a long lived radioactive element which is naturally present in minute concentrations in igneous, sedimentary and metamorphic rocks. These rocks when subjected to weathering results in the formation of soil which also has traces of uranium. Distribution coefficient (Kd) is a crucial parameter in environmental assessment which is used to predict the interaction and transport of uranium in groundwater. The objective of the study is to estimate the Kd of uranium in soils and to develop a relation between this and the soil parameters. Seven rock samples and twenty three soil samples were collected during this study. The Kd of rock samples of different grain sizes where determined and the soil samples were analysed for electrical conductivity, pH, grain size, bulk density, particle density, porosity, calcium carbonate, cation exchange capacity and Kd. The Kd of the soil increases with increase in soil pH up to 6, after which it gradually decreases. Multiple regression analysis was performed to quantify the effect of various soil parameters on soil Kd and equations were statistically significant. Thus, soil Kd in a region could be predicted using limited soil properties with such statistically significant equations.

Identification of temperature effect on post-critical geomechanical properties of loaded sandstones

Geomechanical changes in the post-critical residual strength and strain of Carboniferous sandstones from the Upper Silesian Coal Basin, Poland, were measured from uniaxial compression tests. Rock samples were subjected to high temperatures of up to 1200 °C. Sandstone samples of different grain sizes were collected from all currently exploited lithostratigraphic members of coal-bearing Carboniferous sandstones across the Upper Silesian Coal Basin, including the Upper Silesian Sandstone Series (Ruda Beds and Saddle Beds). The samples were heated to temperatures between 100 and 1200 °C, cooled to room temperature, and subsequently tested by uniaxial compression in a servo-controlled testing machine MTS-810 NEW. The analysis of results followed a grain size and room temperature uniaxial compressive strength classification scheme. Normalized indices of the thermal influence on residual strength and residual strain were calculated. The new measure, namely the indices of thermal influence, can be used to predict the stability of rock masses subjected to high temperatures. The conducted research in terms of evaluation of post-critical parameters subjected to high temperatures as well as the method of analyzing the results are novel and are of primary importance from the engineering (mining and geoengineering) applications point of view.

Helium apparent diffusion coefficient and trapping mechanisms in implanted B4C boron carbide

When boron carbide is irradiated in nuclear reactors, large helium quantities are produced due to the (n,α) neutron absorption reactions. In a recent paper, we have identified the trapping sites for helium, grain boundaries and damaged zones. In this paper, we propose the determination of an apparent diffusion coefficient for helium. 3He implantations then annealing were performed in B4C samples of different grain sizes. The 3He(2H,α)1H nuclear reaction was used to profile helium before and after annealing. Helium profiles with two superimposed components were observed. The narrow component is attributed to helium trapped in the implanted, damaged zone, either in clusters too small to be seen by TEM or as helium-defect complexes. The large component evolution is bounded by the distribution of the grain boundaries surrounding the implanted zone, confirming the high trapping efficiency of the grain boundaries. From an Arrhenius plot, an activation energy for helium diffusion in grains of 2.0 ± 0.2 eV was deduced in a large grain size material.

Study of Radon and Thoron exhalation from soil samples of different grain sizes

The exhalation of radon (222Rn) and thoron (220Rn) from a porous matrix depends on the emanation of them from the grains by the recoil effect. The emanation factor is a quantitative estimate of the emanation phenomenon. The present study is to investigate the effect of grain size of the soil matrix on the emanation factor. Soil samples from three different locations were fractionated into different grain size categories ranging from <0.1 to 2mm. The emanation factors of each of the grain size range were estimated by measuring the mass exhalation rates of radon and thoron and the activity concentrations of 226Ra and 232Th. The emanation factor was found to increase with decrease in grain size. This effect was made evident by keeping the parent radium concentration constant for all grain size fractions. The governing factor is the specific surface area of the soil samples which increases with decrease in grain size

Influence of grain size on radionuclide activity concentrations and radiological hazard of building material samples

The knowledge of radioactivity content in various radionuclides in building materials plays an important role in health physics; therefore, we measured the amount of naturally occurring radionuclides in building material (sand, granite, marble, and limestone) samples of different grain sizes by using NaI (Tl) and MCA1024 gamma-ray spectrometers. Data analyses were performed to determine 226Ra, 232Th, and 4°K activity concentrations. The results revealed an inverse relationship between activity concentration and grain size of the samples. The radium equivalent activity (Raeq), representative level index I, and annual absorbed dose rate were calculated.

Effect of initial grain size on microstructure and mechanical behavior of cryorolled AA 5083

The effect of initial grain size on microstructure and mechanical behaviour of Al-Mg (AA 5083) alloy was investigated by subjecting it to rolling at liquid nitrogen temperature (CR-cryorolling) up to various strains. Initial samples of different grain sizes, ∼ 12 μm and 100 μm and with 8 mm thickness were prepared by processing through rolling followed by annealing. Mechanical properties were investigated by employing hardness and tensile testing. Microstructural studies were carried out by using electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM) techniques. CR up to 2.3 true strain has resulted ultrafine grained (UFG) structure with improved mechanical properties. Effect of annealing on microstructure and mechanical properties of the material with different initial grain sizes CRed up to true strain 2.3 was investigated by performing short annealing at 300 °C for 5 min. At lower strain (true strain-0.3) the change in hardness and ductility was not significant due to low dislocation density. On further increase in strain (true strain-2.3), the fine grained material has shown improved hardness (134 HV) and ultimate tensile strength (UTS) (510 MPa), as compared to coarse grain material with hardness (125 HV) and UTS (475 MPa). It has been observed that during annealing the microstructure evolution through recovery and recrystallization progresses faster in fine grained material due to large volume fraction of grain boundaries which acts as active sites for nucleation. Fully homogenous ultrafine grained structure with grain size in the range of 100-500 nm was obtained in fine grained material. The role of second phase particles on grain refinement was also investigated.

Estimation of surface iron oxide abundance with suppression of grain size and topography effects

Mineral forms of iron oxide, such as hematite, goethite and jarosite, are important because they are widely distributed at the Earth’s surface and because they are used as indicators for mineral exploration. Iron oxide abundance in rocks containing these minerals can be estimated from the absorption depth at wavelengths of around 900nm in a reflectance spectrum, but this depth is also affected by extraneous factors such as grain size and topography. This paper investigated the effect of grain size on reflectance spectra and proposed a method for estimating iron oxide abundance in surface rocks by using remotely sensed data with suppression of the effects of grain size and topography. Reflectance spectra were measured in a laboratory from rock powder samples of different grain sizes containing iron oxide minerals. While the reflectance increased with decreasing grain size, the presence of ferric iron caused the absorption depth to be almost constant at around 900nm, irrespective of the chemical composition of the sample. In addition, the difference between the reflectance at 550nm and 760nm (Slope) was a function of grain size. Iron oxide abundance can be estimated accurately by MCR-900D, which is the maximum absorption depth at the absorption center after the effect of grain size and topography was suppressed by Slope and the continuum-removal method, which takes the ratio between the original spectrum and its continuum, respectively. Correlation of MCR-900D results with datasets of actual spectral and chemical iron oxide laboratory measurements revealed that the mineral forms also need to be considered. MCR-900D results were significantly correlated with rock samples classified as containing different forms of iron oxide minerals (hematite, goethite and jarosite). Finally, MCR-900D was applied to an AVIRIS dataset for the Cuprite site in Nevada, USA. The results represented the enrichment zones of iron oxide within hydrothermally altered areas.

Experimental investigations of grain size effects in forward microextrusion

Micromanufacturing has received good attention globally in terms of its manufacturing methods and processes. One of the most popular micromanufacturing processes is microforming. Although there were efforts made to realize microextrusion for industrial application, the technology itself was seen as being insufficiently mature and unlike conventional methods, there is no in-depth knowledge. It has become essential to develop a proper understanding which in turn could be used to develop dedicated processes for the manufacturing of metallic microcomponents. In this work, an attempt has been made to realize this special application of metal forming. A novel experimental setup consisting of forward extrusion assembly and a loading setup has been developed to obtain the force-displacement response. The effects of miniaturization on microcomponents and the material behavior during forward extrusion are investigated using a computerized universal testing machine (UTM). As per industrial requirement and application of micropart in micromanufacturing process, grain size is an important factor. By using a forming assembly in conjunction with a loading setup, the authors are able to investigate the force-displacement response for microextrusion with material of different grain sizes. Extrusion tests performed on the samples of different grain sizes demonstrated that decreasing grain size caused an increase of flow stress. The realization of such a productive forward extrusion assembly poses significant advantages when compared to the conventional manufacturing technologies in the production of microparts.

Hydrogenated Grain Boundaries Control the Strength and Ductility of Polycrystalline Graphene

In the growth of polycrystalline graphene via chemical vapor deposition, grain boundaries (GBs) were shown to be energetically favorable sites for hydrogenation. Thus, it is of both scientific interest and technological significance to understand how hydrogenation on GBs affects the mechanical properties of polycrystalline graphene. Here we perform molecular dynamics simulations to investigate the mechanical properties of hydrogenated polycrystalline graphene. Our simulations reveal that the fracture strength of hydrogenated polycrystalline graphene is significantly reduced by the combined weakening effect of bond prestraining in highly defective GBs and sp3 hybridization of hydrogenated GB atoms. In addition, this reduction in fracture strength due to GB hydrogenation is observed in polycrystalline graphene samples of different grain sizes ranging from 2.5 to 10 nm. Our findings show that the loss of mechanical strength due to GB hydrogenation must be taken into account in the application of polycrystall...

Bulk and nanocrystalline electron doped Gd0.15Ca0.85MnO3: Synthesis and magnetic characterization

Polycrystalline Gd0.15Ca0.85MnO3 sample was prepared by solid state reaction method and nanocrystalline samples of different grain sizes of the same were prepared by sol–gel method. Phase purity and composition were verified by room temperature X-ray diffraction and SEM-EDAX analysis. Magnetization data of bulk Gd0.15Ca0.85MnO3 in 5kOe field shows a peak at ~119K (TN) suggesting an antiferromagnetic transition. Nanocrystalline Gd0.15Ca0.85MnO3 sample (~54nm size) also shows a cusp at ~107K and a broad thermal hysteresis between field cooled cooling (FCC) and field cooled warming (FCW) data around this temperature. This thermal hysteresis suggests possible crystal structural transition. Field variation of magnetization of bulk Gd0.15Ca0.85MnO3 at 5K shows a tendency to saturate, but yields a magnetic moment value of only ~1.12μB/f.u. in 70kOe. The value of magnetization of nanocrystalline sample at 5K in 70kOe field is slightly larger and is ~1.38μB/f.u. which is probably due to the surface moments of the nanoparticle samples. Both the samples show Curie–Weiss-like behaviour in their paramagnetic state.

Shear test and physical mechanism analysis on size effect of granular media

Shear test samples of different grain sizes are prepared by using mineral particles of soil, and a series of tests of quick direct shear and tri-axial shear are performed to study the size effect of granular media. Deformation curves and shear stress strength are given of test samples with particles of different size and volume fraction. On the basis of the ratio of micro-acting forces between particles to gravity and the cell element model, physical mechanism of grain size effect is, for the first time as far as we know, explained on the micro-level and mecro-level respectively. Test results show that the deformation characteristic of granular media is enhanced and its shear stress strength increases with increasing volume fraction and decreasing of particle size, and the effect of volume fraction on the deformation characteristics and strength is more notable than that of grain size. According to mechanism analysis on size effect, parameter ratio of micro-acting forces to gravity is suggested to assess aggregation and friction effects of particles in the media, and mecro-mechanism is interpreted as strain gradient and micro-cracks of deformation coordination leading to grain size effect. The cell element model presented in this paper can greatly reduce the degrees of freedom of granular media and provides an available way for calculation modeling in industry and engineering design.