Homogeneous Grain Size Research Articles

The combined effects of carbides and martensite blocks heterogeneity on the fatigue life scatter in bearing steel

With the mitigation of inclusion-related harm through purifying methods, the fatigue life scatter of bearing steels is now predominantly governed by microstructural heterogeneity. This work employs an integrated experimental-numerical approach to elucidate the microstructure-related localized plastic strain in 52100 bearing steel under cyclic loading. We observed significant localized plastic strain in the coarse grains adjacent to aggregated carbides after unloading, which may act as a precursor to fatigue cracks and contribute to fatigue life scatter. This strain arises from two primary factors: stress concentration due to aggregated carbides and the relatively lower strength of coarse matrix grains, which is usually overlooked. Enhancing the homogeneity of both carbide distribution and matrix grain size will be a strategy to reduce the fatigue life scatter of bearing steels.

Experimental investigation on rock microfabrical effects on dynamic hardness behaviour

Rocks' physicomechanical properties are influenced by their textural qualities. Rock mass stability is largely governed by these variables. Many geoengineering facilities depend on the capability to assess both short and long-term rock behaviors based on the interaction between different textural characteristics and physicomechanical properties. Rock hardness is frequently used in excavation engineering and is measured by several methods with different mechanisms. The Leeb dynamic hardness method has been recently applied in rock engineering applications as a new, inexpensive, non-destructive, and portable technique. This paper aims to show the interaction between the quantitative microfabrical features and the Leeb hardness of the rocks. For this purpose, 33 various rock types were chosen by considering their physicomechanical properties and microfabrical characteristics. Thin sections were prepared and their microphotographs were analyzed by ImageJ software. Four basic characteristics, including grain perimeter and area and length of minor and major axes, were measured. Then, seven textural quantities, including equivalent diameter (Dequi), shape factor (SF), aspect ratio (AR), grain compactness (C), texture coefficient (TC), interlocking index (g), and grain size homogeneity (t), were calculated based on those basic parameters and statistically analyzed. The findings indicate that the Leeb hardness increases with increasing the grain area and perimeter, equivalent diameter, grain compactness, homogeneity of grain size, grain interlocking, and TC. In contrast, Leeb's hardness decreases with increasing the AR and SF. The texture coefficient reveals the most meaningful relationship (R2 > 0.8) with the Leeb dynamic hardness test among the studied microfabrical characteristics in sedimentary and igneous rock samples.

Talc schist deposits from central Cameroon: Mineralogical and physico-chemical characterization

Talc schist deposits are reported in central Cameroon region, and different alteration zones were determined depending on differences related to the texture and color of the host rock. For the purpose of determining mineralogical and physicochemical characteristics of talc schist, a total of 45 samples from the sites studied were collected and analyzed using an array of physico-chemical methods.Talc schist samples are mainly composed of variable amount of talc associated with plagioclase and clay minerals. Three groups of mineral association were determined: i) talc with small amount of chlorite and traces of kaolinite, ii) talc with high amount of chlorite, iii) variable amount of talc with plagioclase and clay minerals. The talc schist samples have homogeneous grain-sizes and are classified as silty sand or sandy silt.The occurrence of Ni and Cr in the talc schists are consistent with the composition of the talc deposits formed in relation to ultramafic rocks. The genesis of talc is due to hydrothermal fluid circulation in ultramafic rocks, attested by the occurrence of S and P.

Textural and oceanographic aspects of the sandy beaches of South coast of Santa Catarina, Brazil

This study aims to describe the textural and oceanographic aspects of the foreshore zone of the beaches located between the municipalities of Passo de Torres and Balneario Rincao, at South coast of Santa Catarina. Oceanographic and textural parameters were collected at 41 sites, arranged on 22 beaches that extend out on 77,4 km of coastline. The field work was conducted in December 2007. The Sysgran software analyzed the textural data, revealing high homogeneity of grain size, predominance of fine sand, with quartzose sediments, reddish brown color (2.5YR5/3) in 66% of the samples and brown color (10YR5/3) in 34% of the samples, besides reducing amount of organic matter and biodetritic carbonate. In general, the sediments are well sorted, mesokurtic and with skewness approximately symmetrical. Regarding the source area, it should be noted that the coastal plain of the South coast of Santa Catarina comprises a wide barrier-lagoon depositional system of Holocene age, in which the sediments in general show high maturity. Regarding the coastal oceanographic aspects, the rectilinear shape of the coastline, as well as the predominant dissipative morphodynamic stage and a system of well-developed coastal dunes in most of the sites examined, corroborate with the textural and compositional homogeneity resulting from the frequency and intensity of the marine dynamic agents, winds and supply of lithoclastic sediments.

Effect of Temperature Gradient on the Grain Size Homogeneity of SEED Produced Semi-Solid Slurries by Phase-Field Simulation.

The distribution homogeneity of grain size affects the fluidity of the semi-solid slurry, which in turn affects the properties of the casting. One key factor affecting grain size uniformity resides in the nucleation number, which has been studied thoroughly, while the other factor is temperature gradient which has not been investigated yet. In this study, the microstructure evolutions under certain temperature gradients are investigated by experiment and simulation using a two-dimensional quantitative phase-field (PF) model. A parallel and adaptive mesh refinement algorithm is adopted to solve the nonlinear phase-field equations. The results indicate that temperature gradient can affect the size distribution of microstructure in the semi-solid slurry prepared by the SEED process. A higher temperature gradient (in the range of 0.230~0.657 °C/mm) along the radial direction is beneficial to the homogeneity of the grain size in a slurry.

Sintering temperature and XPS analysis of Co2.77Mn1.71Fe1.10Zn0.42O8 NTC ceramics

Microstructure and electrical properties of Co2.77Mn1.71Fe1.10Zn0.42O8 (CMFZ) ceramics as a function of temperature were studied in the sintering process. The optimum sintering temperature of 1200 °C is determined to obtain the optimum microstructure and electrical properties. Both microstructure and electrical properties are sensitive to the different sintering temperatures. In particular, the appropriately increased sintering temperature enhances the densification and the homogeneity of grain size. However, the accelerated grain growth with a large number of closed pores appears when above the optimum sintering temperature. The electrical resistivity first increases and then decreases with the increased sintering temperatures. The ρ25 and B25/50 constant are in the range of 3072–4238 Ω cm and 4021–4056 K, respectively. X-ray photoelectron spectroscopy (XPS) was analyzed the evolution of resistivity clearly and proved the n-type semiconductor of CMFZ ceramics.

The Effect of Variable-Frequency Ultrasonic Melting Treatment Technology on Microstructure and Properties of AZ80 Magnesium Alloy

The traditional fixed-frequency ultrasonic technology (FUT) and the variable-frequency ultrasonic technology (VUT) were used in direct-chill (DC) casting of an AZ80 magnesium alloy with the diameter of ∅255mm. The microstructure evolution, mechanical properties and macro-segment of Al element were investigated. The results show that both FUT and VUT can refine the α-Mg grain while the VUT has better efficiency which can reduce the grain size from 679-1454 μm (DC) to 150-241 μm. The homogeneity of grain size was also improved. These two technologies can also change the morphology and distribution of Mg17Al12 phase and tiny and refined morphology of Mg17Al12 phase and a homogeneous distribution can be obtained after VUT treatment. The YS and UTS were increased following the microstructure evolution, displaying the YS of 88.9-95.1 MPa and UTS of 164.3-173.1 MPa after VUT treatment. The segregation rate of Al element were improved with VUT treatment. Keywords: magnesium alloy; variable frequency ultrasonic technology; microstructure; mechanical properties;

Diffusion in Condensed Matter by Finite Element Method

In this Chapter, the finite element simulations of diffusion processes in homogeneous and polycrystalline materials are presented as well as some analytical solutions and implementations of basic diffusion relations. For the homogeneous materials the presented examples show the changes in time of the concentration of diffusing matter within the semi-infinite system and simulation of anisotropic nature of diffusion processes.The polycrystalline materials have been analysed for three cases, namely influence of average grain size and the homogeneity of grain size on the macroscopic diffusivity as well as simulation of the diffusion strains. The homogenisation technique has been used to estimate the diffusion property of grains aggregates.

Growth of TiO2 Thin Films by High Energy Milling Assisted Pulsed Laser Deposition Method

TiO2 thin film can be deposited on the silicon substrate using pulse laser deposition method. To prove homogeneity of grain size on surface, this study uses milling treatment for TiO2 powder before it is deposited. Milling treatment was conducted on samples of commercial TiO2 powder with high energy milling method. The variation of milling time was 0, 1, 3 and 6 hours. Furthermore, the samples were shaped as disc with diameter of 1 cm and used as a target source in growth of thin film. Variations in time for the milling treatment of the TiO2 powder has no effect on the phase change, but rather on the homogeneity of grain size on a thin layer of TiO2. In this study, the optimum milling time to produce a homogeneous grain size of a thin layer of TiO2 for 3 hours.

Analysis of grain structure evolution based on optical measurements of mc Si wafers

Grain structure and grain competition have a strong impact on bulk lifetime in multicrystalline (mc) silicon. A fast and thorough characterization of grain structure is crucial in order to improve industrial crystal growth. This work introduces key parameters of grain structure, extracted with a newly developed image processing tool. Four bricks grown with different concepts were chosen to investigate the value of the identified key parameters and to identify characteristic developments along the brick. Optical measurements on as-cut wafers from these bricks serve as a basis to extract grain structure properties, i.e., size, shape, homogeneity and distribution of grain size. By connecting the 2D-information over brick height, a statistical insight into the entire brick is gained. Weighted percentiles of grain area offer a robust measure to characterize grain size distribution. As twinning has a large impact on grain competition, twinned grains are detected via grain shape. Additionally, regions with strong grain competition are highlighted for investigations on grain overgrowth.It is found that the share of twin grains increases with brick height in high-performance mc (HPM) silicon with fine-granular seeds from almost zero up to about 15% whereas it remains rather constant over the whole brick height in standard mc-Si. The results of the investigated bricks show clearly that towards the brick top, the material differences in grain size decrease. This suggests that an energetically favorable state may exist for grain structure development.

Permeability spectral analysis and micro-structural parameter determination for yttrium-excess polycrystalline yttrium iron garnet

In this study, we describe the variation of the real (μ′) and imaginary (μ″) parts of complex permeability for polycrystalline samples of the garnet system: Y3+xFe5−xO12, x = 0.0, 0.2, 0.4 and 0.6, over the ranges of frequency (f = 100 Hz–13 MHz) and temperature (T = 300–700 K). It is found that the higher concentration of Y3+ substitution (x ⩾ 0.4) leads to the formation of an unwanted secondary orthoferrite phase and reduces the grain size. The permeability dispersion spectra of the system sintered at 1200 and 1500 °C are of resonance type and relaxed type, respectively. It has been demonstrated that not only grain size but also uniformity and homogeneity of grain size play a key role in governing the nature of the permeability spectrum. The maximum of μ″ near the Neel temperature has been attributed to a damping effect of domain wall motion. Various micro-structural parameters have been determined and discussed in a systematic manner.

Source as a controlling factor on the quality and interpretation of sediment magnetic records from the northern North Atlantic

Magnetic properties of eight particle size ranges from nine locations in Iceland and 26 locations in southern Greenland reveal the importance of source variation for our understanding of paleomagnetic and environmental magnetic records in the marine environment. These terrestrial samples show varying degrees of particle size dependence with all samples showing that the silt fraction possesses greater concentrations of ferrimagnetic minerals than either clay or sand. Fine pseudo-single domain (PSD) size magnetic grains dominate the magnetic assemblage of all Icelandic fractions. In contrast, Greenlandic samples possess greater variation in magnetic grain size; only fine silt and clay are as magnetically fine as the Icelandic PSD grains, while Greenlandic silts and sands are dominated by coarser PSD and multi-domain grains. These observations from potential marine sediment sources suggest that the silt size fraction is a likely driver for much of the concentration-dependent parameters derived from bulk magnetic records and that the magnetic grain size of the silt fraction can be used to discriminate between Icelandic and Greenlandic sources. Using these results to examine magnetic grain size records from marine sediment cores collected across the northern North Atlantic suggests that source, not just transport-controlled physical grain-size, has a significant impact on determining the magnetic grain size at a particular location. Homogeneity of magnetic grain size in Icelandic sediments at least partially explains the consistent quality of paleomagnetic records derived from cores surrounding Iceland and their ability to buffer large environmental changes.

Numerical Simulation and Process Optimization of Directional Solidification of Nb Containing High Silicon Steel

Fe-6.5%Si alloy is an excellent soft magnetic material. However, the industrial production of this sheet was difficult, due to its room temperature brittleness. In order to improve its deformation performance, the directional solidification and inhibitor of Nb were investigated in this study. Rod samples of Φ6.8 mm×100 mm were used both for modeling and experiments. ProCAST-finite element analysis was employed for the modeling with a temperature gradient of 1150K/cm (from 1450°C to 300°C) for directional solidification and the drawing velocities of 10, 35, 60, and 100μm/s. Calculations were carried out on the concerning temperature gradient, solidification rate and grain growth. The results showed that small amount of Nb, with optimized drawing velocity of 60μm/s was helpful for the homogeneity of grain size, which could improve the ductility for subsequent deformation processes.

Nonradiative and Radiative Recombination in CdS Polycrystalline Structures

Properties of polycrystalline CdS layers, employed in formation of the CdS-Cu2S heterostructures, have been studied by combining contactless techniques of the time and spectrally resolved photoluminescence (TR-PL) spectroscopy and microwave-probed photoconductivity (MW-PC) transients. The confocal microscopy has been employed to correlate the homogeneity of photoluminescence and grain size in CdS layers. Three types of samples with crystallite grain size of <1 μm (the I-type) and of 2–10 μm of homogeneous (II-type) and inhomogeneous (III-type) grain distribution have been separated. The simultaneous record of MW-PC and TR-PL responses ensures the same sampling area on the layer under investigation, as both (MW-PC and TR-PL) signals are generated by the same UV laser excitation beam. Two PL bands peaked at 500 and 700 nm were revealed. It has been demonstrated that photoluminescence intensity strongly depends on the properties of the polycrystalline 15–26 μm thick CdS layers with equilibrium carrier density of about1.5×1013 cm−3, which serve as the substrates to form CdS-Cu2S junctions. The different carrier decay components were ascribed to different microareas with characteristic MW-PC and PL decay lifetimes of 2–10 ns, ascribed to microcrystallites with PL instantaneous decay lifetimes of 40–200 ns, and MW-PC decay lifetimes in the range of 100–1000 μs attributed to the inter-crystallite areas of CdS polycrystalline material.

Effects of Manganese on Microstructure and Mechanical Properties of AZ31 Magnesium Alloy Processed by Differential Speed Rolling

A DSR processing with a roll speed ratio of 1.08 was carried out on an AZ31 alloys with Mn additions of 0, 0.2, 0.4 and 0.6 wt.% for investigating the effects of Mn on the microstructural evolution and mechanical properties. The amount of the Al-Mn compounds increased with increasing the Mn content. Compare with the DSR processed sheet without Mn addition with a homogeneous grain size, those with Mn additions exhibited an inhomogeneous microstructure due to the appearance of the shear bands comprising the small grains around 5 μm. The Mn addition exhibited a significant effect in grain refinement even for a low content of 0.2 wt.%, which reduced the average grain size from about 25 μm to 10 μm. The Mn addition resulted in the significant increases in the tensile strength and the 0.2% proof stress by about 25 MPa and 40 MPa, respectively.

Spatial distribution of macrobenthic fauna on three sandy beaches from northern Rio Grande do Sul, southern Brazil

The spatial distribution of benthic macrofauna on the beaches of Tramandaí, Jardim do Éden and Harmonia, was investigated over five consecutive days in April, 2003. The distribution pattern was also analyzed along with environmental parameters. Three transects were set on each beach, 50 m apart, with four sample stations set along each transect. On every station, three samples of benthic macrofauna were taken daily, with a core sampler with 20 cm diameter. In the midlittoral zone, the polychaete Euzonus furciferus and the isopod Excirolana armata dominated. In the swash zone, tidal migrators, Emerita brasiliensis,Donax hanlevanus and Mesodesma mactroides, were the most abundant species and, on some days, the polychaete Scolelepis gaucha. In the lower zones of the beaches, D. hanleyanus,M. mactroides and the amphipod Puelche orensani dominated. This zonation pattern was found for all three studied beaches, based on the average density of each species, over the five days period. Horizontal variation in the fauna was not found, either inter or intra the studied beaches, possibly due to little variability in slope and homogeneity of sediment grain size presented in the three beaches.

ReMnO3(Re:Ho, Er) 박막의 강유전성에 미치는 열처리 공정의 영향

Ferroelectric ReMnO₃ (Re:Ho, Er) thin films were deposited on Si(100) substrate by Metal-Organic Chemical Vapor Deposition (MOCVD). Crystallinity and electric properties of ReMnO₃ (Re:Ho, Er) thin films were investigated as a function of thermal heat treatment process, CHP (Conventional Heat-treatment Process) and RTP (Rapid Thermal Process). ReMnO₃ (Re:Ho, Er) thin films prepared by RTP showed higher c-axis preferred orientation and homogeneous surface roughness than those prepared by CHP. The remnant polarization of ferroelectric hysteresis loop of ReMnO₃ (Re:Ho, Er) thin films was strongly dependent on the c-axis preferred orientation of hexagonal single phase, and the leakage current characteristics of thin films were dependent on the homogeneity of grain size well as surface roughness of thin films.

Rare earth doped new cemented carbide with Ni-Co binder for mining

A method, doping WC with La(NO3)3, of producing cemented carbide with rare earth was introduced. The effects of lanthanum on the mechanical properties and microstructure of WC-9(Co-75%Ni) cemented carbide were studied and a rock drilling experiment was carried out. The experimental results show that both transverse rupture strength (TRS) and hardness of WC-9(Co-75%Ni) rare earth cemented carbides can match that of WC-9Co cemented carbide, when La2O3/(Co + Ni) ratio is 0.3%, the abnormal growth of WC grain in the cemented carbide can be restrained effectively, the homogeneity of grain size in microstructure and the wear resistance are improved, which can be matchable to that of WC-9Co cemented carbide for mining.

Mechanical activation conditions of the Fe 2O 3 and V 2O 3 mixture powders in order to obtain a nanometric vanadium spinel ferrite

Co-milling of iron and vanadium oxides allows to obtain an intimate oxides mixture at a nanoscale, similar to a coprecipitate elaborated by soft chemistry. Reduction of such a mixture in the same temperature and oxygen partial pressure conditions (500°C and 10 −25 Pa) as the soft chemistry products leads to a nanometric vanadium ferrite with the only spinel phase. The characterization of the powders is achieved by X-ray diffraction (XRD), scanning electron microscopy, infrared (IR) spectrometry, thermogravimetry and calorimetry. Homogeneity of grain size and chemical composition is reached if the initial oxides have similar grain size.

Relative paleointensity of the geomagnetic field during Brunhes Chron recorded in North Pacific deep-sea sediment cores: orbital influence?

Relative paleointensity records of the geomagnetic field during the Brunhes Chron were obtained from two sediment cores in the North Pacific near the Hess Rise. The cores, taken below the carbonate compensation depth (CCD), showed an oxidized environment, and accompany little paleoclimatically induced lithological changes. Homogeneity of magnetic mineralogy and magnetic grain size, which are prerequisites for sedimentary paleointensity, were thoroughly examined using various techniques including low-temperature magnetometry, room-temperature hysteresis parameters, and S ratio. Isothermal remanent magnetization (IRM) was used as a normalizer of the natural remanent magnetization (NRM). The appropriateness of the normalization was checked by the absence of correlation between the normalized intensity (NRM/IRM) and the normalizer (IRM). The relative paleointensity records obtained are generally similar to the datasets from the east and central equatorial Pacific. Spectral analysis showed significant power at the orbital eccentricity (100 kyr) frequency in the relative intensity record, but not for the normalizer. This suggests orbital influence on the geomagnetic field intensity, but the possibility of paleoclimatic contamination through rock-magnetic changes should be examined further using cores from different sedimentary regime.