Narrow Grain Research Articles

ESTABLISHMENT OF TECHNICAL REQUIREMENTS REGARDING DRAINING ASPHALT CONCRETE

Introduction. It has been established that porous draining asphalt concrete (DAC) is an open-frame asphalt concrete that is specially designed with a high content of air voids, which are designed to remove water from the surface of the road surface. Pavement surfaces that include draining asphalts, permeable wear courses, and porous asphalt pavements are gaining more and more acceptance in the road industry worldwide. Drainable asphalt can be susceptible to freeze-thaw damage in cold climates and will require winter maintenance practices. The service life of such coatings varies greatly depending on climatic conditions, intensity of traffic and loads, design and construction methods. Drainage asphalt pavements were created to increase road safety, but in addition to high traction characteristics, they have high porosity, which provides water permeability, which reduces the amount of surface water and thus reduces the formation of splashes in rainy weather. This leads to a reduction in the risk of aquaplaning and an increase in road visibility, and ultimately to an increase in road safety.. Problem statement. The issue of timely removal of surface water from the road surface is mandatory and is solved by providing the road surface with a transverse slope. As practice shows, this does not sufficiently protect the road surface from the negative effects of water. High operational safety, improvement of the operational characteristics of the road surface is achieved due to the removal of the accumulation of water stains from its surface, which reduce the adhesion of the wheels to the road surface. These qualities can be improved by introducing draining asphalt concrete. However, the service life of draining asphalt concrete varies greatly depending on climatic conditions, traffic intensity and loads, design concepts and construction methods. In order to further improve the current state-of-the-art instructions for the production and application of DAC to solve regional, road and climate problems, a comprehensive analysis of the currently available applications of DAC mixtures for the construction and maintenance of road surfaces is necessary. Therefore, on the basis of this, today in Ukraine it is expedient to introduce normative documents that would regulate the design, manufacture, technical requirements and performance of works according to this technology, which would allow for practical use, optimization and development of the road industry of Ukraine in this direction. Purpose. Production of asphalt concrete mixtures and arrangement of road surface from draining asphalt concrete. Assessment of the regulatory framework of the world and establishment of recommendations and technical requirements for the production and installation of draining asphalt concrete. Materials and methods. Experimental and experimental-analytical. Results. An analysis of the existing experience of using draining asphalt concrete, conditions of its use, was carried out. Theoretical studies of the process of forming asphalt concrete with a structure of interconnected open pores. Experimental studies on the selection of grain composition and bitumen content in draining asphalt concrete have been conducted. Recommendations for the production of draining asphalt concrete mixtures and the arrangement of a covering from them have been developed. Conclusions. An important role in the operational reliability and durability of draining asphalt concrete is played by the properties of the components, as well as the ratio between mineral materials and bituminous binder. In European countries, the greatest attention is paid to the narrow grain composition of mixtures, especially the requirements for large aggregates and bituminous binders. For the production of drainable asphalt concrete, crushed stone of narrow fractions is used, since it has a special granulometric composition, unlike typical dense and crushed-mastic asphalt concrete, it has sufficiently large porosity and requires extremely high attention and strict requirements for crushed stone materials. Therefore, an important step for the implementation of a promising construction technology would be the development of recommendations for draining asphalt concrete in Ukraine, which will include technical requirements, recommendations for design and application, acceptance rules and control methods.

Molecular dynamics simulation study on mechanical properties of Janus MoSSe monolayer

This work systematically studies the mechanical responses of a novel semiconducting Janus MoSSe monolayer subjected to uniaxial tensile loadings by molecular dynamics simulations. It is found that the Janus MoSSe monolayer shows clearly anisotropic responses along armchair direction and the zigzag direction. The phase transition behavior is observed when the Janus MoSSe monolayer is under the action of tension along the zigzag direction at temperatures below 100 K, while it does not exist in any other conditions. The Young’s modulus, ultimate strength and ultimate strain decrease with temperature increasing. Particularly, the ductile-to-brittle fracture behavior is observed when uniaxial tension is applied along the zigzag direction depending on temperatures. The underline fracture mechanism is analyzed. Moreover, mechanical properties of Janus MoSSe monolayer with various grain boundaries are also carefully explored. It is found that the ultimate strength and ultimate strain depend more sensitively on narrow grains than on those wider ones. The crack is initialized near the grain boundaries and propagates along the direction almost perpendicular to the grain boundaries. The findings of this work may shed light on design and optimization of nanoscale electronic devices based on the Janus MoSSe monolayers.

Formation of Remote Quantum Point Contact Inside Dielectric Medium of an AlO x /SiO x ReRAM

Remote quantum point contact (QPC) far from the metal electrodes was observed in forming free aluminum oxide (AlOx)/silicon oxide (SiOx) resistive random access memory (ReRAM) cell, which was resolved at low bias. QPC behavior of the cell was attributed to confined oxygen vacancies across uncorrelated narrow grain boundaries of intermediate O3 treated thin AlOx layer of the stack, which was designed to restrict vacancy channeling between the two immediate reservoirs; i.e., from beneath SiOx to the top as-deposited AlOx layer. From time dependent dielectric breakdown (TDDB) characteristics of the cell while assessed under low stress biases, we found one to one correspondence between TDDB and its bias dependent QPC. Furthermore, we found that, under steady state and especially at low biases progressive breakdown (PBD) of the dielectric exhibited two-level random telegraph noise (RTN) like conductance fluctuations, which occurred in the magnitude of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${G}_{{0}}$ </tex-math></inline-formula> or in its multiples depending on applied bias to the cell, that demonstrated a correlation between electron trapping and maximum QPC instability during filament growth. Low voltage QPC-based switching under dc bias sweep, its correlation with TDDB and RTN under the steady state thus provided us a framework to analyze the evolution of QPC well before reaching the SET state in an AlOx/SiOx cell, which is different from the usual QPC evolution as found near contact regions in a conventional SiOx cell without accompanying engineered AlOx barrier.

Low-temperature ozone treatment for p-xylene perm-selective MFI type zeolite membranes: Unprecedented revelation of performance-negating cracks larger than 10 nm in polycrystalline membrane structures

We report that low-temperature ozone calcination allowed MFI type polycrystalline zeolite membranes to maximize their p-/o-xylene separation factor (as high as ca. 2000) by suppressing defect formation. Conventional high-temperature calcination and rapid thermal processing, which provide poor and marked p-/o-xylene separation abilities, respectively, were used for comparison. The corresponding defect structures were quantitatively analyzed by image processing of fluorescence confocal optical microscopy images combined with membrane permeation modeling, revealing the main defects (grain boundary defects and cracks) and their tortuosity, porosity, and size. To the best of our knowledge, we, for the first time, demonstrated that in contrast to common belief, the minor portion of wider cracks instead of the major portion of narrower grain boundary defects determined the final permeation rates. Specifically, the MFI membrane prepared by high-temperature calcination contained many grain boundary defects (narrow; ca. 1 nm) and few cracks (wide; ca. 20 nm) that accounted for ca. 0.1% and 99.8%, respectively, of the slowly permeating o-xylene molar flux. In contrast, the ozone-treated MFI membranes, which only possessed grain boundary defects, achieved the high p-/o-xylene separation performance, underlining the need for the selective reduction in the number of wider cracks rather than ubiquitous, narrow grain boundary defects.

Fiber Laser Welded Cobalt Super Alloy L605: Optimization of Weldability Characteristics.

The present study describes the laser welding of Co-based superalloy L605 (52Co-20Cr-10Ni-15W) equivalent to Haynes-25 or Stellite-25. The influence of laser welding process input parameters such as laser beam power and welding speed on mechanical and metallurgical properties of weld joints were investigated. Epitaxial grain growth and dendritic structures were visible in the weld zone. The phase analysis results indicate the formation of hard phases like CrFeNi, CoC, FeNi, and CFe in the weld zone. These hard phases are responsible for the increase in microhardness up to 321 HV0.1 in the weld zone, which is very close to the microhardness of the parent material. From the tensile strength tests, the ductile failure of welded specimens was confirmed due to the presence of dimples, inter-granular cleavage, and micro voids in the fracture zone. The maximum tensile residual stress along the weld line is 450 MPa, whereas the maximum compressive residual stress across the weld line is 500 MPa. On successful application of Response Surface methodology (RSM), laser power of 1448.5 W and welding speed of 600 mm/min i.e., line energy or heat input equal to 144 J/mm, were found to be optimum values for getting sound weld joint properties. The EBSD analysis reveals the elongated grain growth in the weld pool and very narrow grain growth in the heat-affected zone.

Effect of three-dimensional deformation at different temperatures on microstructure, strength, fracture toughness and corrosion resistance of 7A85 aluminum alloy

In this study, 7A85 aluminum alloy was subjected to 20% three-dimensional (3D) deformation at different temperatures (−196, 25, 250, and 480 °C), followed by solid solution, water quenching, 3% cold deformation, and retrogression and re-aging (RRA) treatment. The microstructural evolution and 3D mechanical properties, fracture toughness, electrical conductivity, and corrosion resistance of the alloy under different deformation processes were analyzed for comparison. The results indicated that conducting the 3D deformation process prior to solution treatment significantly improved the strength and fracture toughness of the alloy as compared to the undeformed (UD) specimen, and maintained its good corrosion resistance under the RRA treatment. In addition, with the decrease of the deformation temperature, the greater flow stress strongly sheared and crushed the coarse second-phase particles into fine particles, thus facilitating their full dissolution in the aluminum matrix during subsequent solution treatment and increasing the driving force for aging precipitation. Furthermore, more dislocations were introduced at low-temperature deformation, thus providing more nucleation sites for static recrystallization during solution treatment and refining grains. Ultimately, the densest precipitates and the finest equiaxed grains with the narrowest grain boundary precipitate-free zones (PFZs) were acquired for the cryogenic deformation (CD) sample, resulting in the highest ultimate tensile strength (UTS), elongation (EL) with the least anisotropy, and fracture toughness of the CD specimen. The optimal comprehensive performance was obtained for the CD specimen with the average 3D UTS, average 3D yield strength (YS), average 3D EL, and fracture toughness of 545 MPa, 476 MPa, 16%, and 42.49 MPa·m1/2, respectively, which were respectively 2.3%, 0.2%, 18.5%, and 21.4% higher than those of the UD specimen.

On the thinnest Al2O3 interlayers in Al‐based nanolaminates to enhance strength, and the role of constraint

Physical vapour deposition combined with atomic layer deposition was exploited to design a model system of UFG aluminium with a narrow grain size and shape distribution, including two types of interfaces (Al-Al & Al-Al2O3), with Al-Al grain boundary orientations exclusively parallel to the loading axis. This enabled isolated study of the strengthening mechanisms that ultrathin oxide layers would provide in a metal multilayer structure. The Al/Al2O3 crystalline/amorphous multilayers with 240 nm metal layers and oxide thicknesses in the range <1 nm–12 nm (i.e. to below the natural oxidation thickness), were microcompressed, yielding a pseudo-macroscopic yield strength of 532 MPa – over 100 MPa higher than the literature-conforming oxide-free reference. The homogenous co-deformation of the structure, with barrelling of the individual metal layers at the micropillar edges, results from the high bonding strength of the metal with its native oxide, meaning no failure or sliding at the interface, unlike previous Al/ceramic multilayer studies. Only the thicker (≥5 nm) oxide layers fractured in-plane: at locations coincident with vertical Al-Al grain boundaries. An analysis of contributions to the strength of these crystalline/amorphous metal/ceramic hybrid multilayers is carried out, identifying the Al-Al2O3 interface to be the crucial factor, rather than the in-plane tensile stiffness and considerable plasticity of ALD Al2O3 itself. The strengthening effect of the oxide layer was effective down to a layer thickness of just 0.5 nm.

Properties of WC–Co hardmetals as a function of their composition and microstructural parameters

Research into WC–Co submicron hardmetals involving measurement of hardness, coercivity and microstructural characterization, as well as analysis and comparison of results from recent literature led to the development of a unified constitutive expression for Vickers hardness in a form that separates the effects of the tungsten carbide grain size from those of the cobalt binder volume fraction. With the proposed expression for HV one may recalculate and compare hardness values for hardmetals featuring the same average grain size but differing in the binder matrix content. The paper shows that, in contrast to the Lee-Gurland model, the proposed constitutive expression framework treats the hardmetal hardness as a function of the carbide skeleton hardness (HWC) and contiguity (C) described as HV = CHWC. The carbide skeleton hardness depends on the WC grain size only, and it is described by the Hall-Petch equation. The results of parallel hardness and coercivity measurements led to an empirical equation relating Hc to the WC grain size and the Co volume fraction. Based on the complete experimental data, the relationship between the coercivity and Vickers hardness was explored, and a simplified relationship between these physical values was proposed to carry out the primary HV evaluation based on the measured coercivity values. As noted in the paper, the above equations are valid for relatively narrow WC grain size distributions with a maximum coefficient of variation of 0.5.

Comparative study of microstructure and mechanical properties using a novel filler rod ER 4943 and autogenously butt welded joint during laser welding of AA 6061-T6 in 1G position

A 4 mm thick heat-treated aluminum alloy AA 6061-T6 has been butt welded in 1 G position using a 12-kW disk laser. A novel high magnesium content filler rod ER 4943 belonging to the 4xxx series of aluminum alloys has been used to investigate its effects on microstructure, mechanical properties and alloying elements segregation in the fusion zone. The results have also been compared with an autogenous laser butt welded joint case. A solidified microstructure has been analyzed by EBSD. It was found that additional solute content brought by filler rod into the molten pool caused a higher proportion of equiaxed grain zone after solidification due to an enhanced constitutional supercooling ahead of solid/liquid interface. For an autogenous butt welded joint, the columnar morphology sustained for a longer period and a narrower equiaxed grain zone were observed. Point analysis by an EDS revealed a higher retention of magnesium and silicon inside the solid solution with filler rod welding. In addition, the area map of magnesium also observed a denser distribution of magnesium inside the fusion zone. Both hardness and tensile strength of filler rod welded joint were higher than without filler rod welding. It is believed that a higher proportion of equiaxed grains and additional solute content within the solid solution are the primary causes of higher mechanical properties owing to hampered dislocation motion. The much desirable results obtained in terms of microstructure and mechanical properties could be of great significance to the welding industry.

ANALYSIS OF THE FACTORS AFFECTING THE GRINDABILITY OF K-FELDSPAR BY THE FULL FACTORIAL DESIGN

This study's aim is to investigate the wet and dry grindability of K-feldspar in a narrow grain size range in a stirred ball mill. In the evaluation of the grinding process, a full factorial design was used to observe the effects of the selected parameters on the dependent variable. On a narrow grain size range grinding, the parameter effects such as ball diameter, stirring speed, grinding time, and interstitial filling ratio were investigated. Experimental results showed that K-feldspar can be efficiently milled with a stirred ball mill in a narrow grain size range (1-10 microns).

Ultrahigh strain in textured BCZT-based lead-free ceramics with CuO sintering agent

• CuO as a sintering agent lowers the sintering temperature of 125 °C, and maintains BCZT-1.0 at a high texture degree of ∼99%. • CuO-based liquid phases eliminate boundaries between templates and matrix powders, release local stress, decrease grain sizes, and increase dielectric dispersion coefficient. • Maximum strain s max of 0.38% and low h s of 5.2% along with homogeneous d 33 ∼780 pC/N and large d 33 * ∼2950 pm/V was obtained in textured BCZT-1.0. Textured BaTiO 3 (BT)-based lead-free ceramics have gained significant attention due to their high piezoelectric coefficient ( d ) and very large field induced strain ( S ). However, costly nano-size raw materials, excessively high sintering temperature and low Curie temperature ( T c ) hinder their device applications. In this work, highly [001] c -oriented (Ba 0.95 Ca 0.05 )(Zr 0.04 Ti 0.96 )O 3 ceramics with x mol% CuO ( x = 0.25, 0.5, 1.0, 2.5) denoted as BCZT- x were synthesized by templated grain growth using micro-sized raw powders. The introduction of CuO sintering agent lowered the sintering temperature by 125 °C to 1450 °C, and the BCZT-1.0 achieved a high texture degree of ∼99%. In addition, the CuO-based liquid phases eliminated boundaries between BT templates and BCZT matrix powders. Such liquid-phase sintering reduced sintering stresses, decreased the average grain size of BCZT-1.0 from 16 μm down to 13 μm, and increased the dielectric dispersion coefficient γ to 1.63. The almost smoothed out T O-T anomaly in the temperature dependence of dielectric permittivity and comparably high T c (> 102 °C) lead to better temperature stability. The narrower grain orientation distribution with full width at half maximum (FWHM) of ∼5.9° and smaller domains with the size of 0.1–0.5 μm in width and 3–8 μm in length were obtained, a high field induced maximum strain S max of 0.38% and low H s of 5.2% have been achieved in BCZT-1.0 textured ceramics together with a high and homogeneous piezoelectric stress coefficient d 33 ∼780 pC/N and very large d 33 * ∼2950 pm/V.

Effect of Plant Density and Propnit Herbicide on the Weeds and Grain Yield of Sorghum

A field experiment was carried out during the spring season of 2020 in the experimental field of the College of Agricultural Engineering Sciences - University of Baghdad - Abu Ghraib to know the effect of weed controlling broad and narrow leaf weeds and grain yield of sorghum (Inqath cultivar). Randomized complete block design (RCBD) was used according to split plots at three replications. The main plots included three weed control treatments (spraying of propnit herbicide at the recommended dose of 450-500 ml dunum-1 and half recommended dose of 225-250 ml donum-1) and weedy and free weedy treatments. In contrast, the subplots included three plant densities (1.0×105, 1.5×105, and 2.0×105, plants ha-1). The results of the statistical analysis indicate that the spraying of herbicides Proponit at the recommended concentration recorded the lowest average density of broad and narrow leaves (7.89 7 and 2.22 plants m-2) and the highest percentage of controlling broad and narrow leaves (72.17 88.03%) and the highest percentage of inhibiting the dry weight (75.33%). As for the effect of plant density, the results indicated that there was a significant effect of plant density in most of the studied traits, where the plant density recorded 200 thousand plants ha-1, the lowest numerical density for broad leaves and the percentage of their control (4.79 plants m-2 and 69.74%), and the plant density recorded 100 thousand The plant ha-1 had the highest inhibition rate of 63.53%. The plant density exceeded 150 thousand plants ha-1, and the highest grain yield was 6.03 tons ha-1. The different combinations between the two studied factors significantly affected most of the studied traits.

The Function of DNA Demethylase Gene ROS1a Null Mutant on Seed Development in Rice (Oryza Sativa) Using the CRISPR/CAS9 System.

The endosperm is the main nutrient source in cereals for humans, as it is a highly specialized storage organ for starch, lipids, and proteins, and plays an essential role in seed growth and development. Active DNA demethylation regulates plant developmental processes and is ensured by cytosine methylation (5-meC) DNA glycosylase enzymes. To find out the role of OsROS1a in seed development, the null mutant of OsROS1a was generated using the CRISPR/Cas9 system. The null mutant of OsROS1a was stable and heritable, which affects the major agronomic traits, particularly in rice seeds. The null mutant of OsROS1a showed longer and narrower grains, and seeds were deformed containing an underdeveloped and less-starch-producing endosperm with slightly irregularly shaped embryos. In contrast to the transparent grains of the wild type, the grains of the null mutant of OsROS1a were slightly opaque and rounded starch granules, with uneven shapes, sizes, and surfaces. A total of 723 differential expression genes (DEGs) were detected in the null mutant of OsROS1a by RNA-Seq, of which 290 were downregulated and 433 were upregulated. The gene ontology (GO) terms with the top 20 enrichment factors were visualized for cellular components, biological processes, and molecular functions. The key genes that are enriched for these GO terms include starch synthesis genes (OsSSIIa and OsSSIIIa) and cellulose synthesis genes (CESA2, CESA3, CESA6, and CESA8). Genes encoding polysaccharides and glutelin were found to be downregulated in the mutant endosperm. The glutelins were further verified by SDS-PAGE, suggesting that glutelin genes could be involved in the null mutant of OsROS1a seed phenotype and OsROS1a could have the key role in the regulation of glutelins. Furthermore, 378 differentially alternative splicing (AS) genes were identified in the null mutant of OsROS1a, suggesting that the OsROS1a gene has an impact on AS events. Our findings indicated that the function on rice endosperm development in the null mutant of OsROS1a could be influenced through regulating gene expression and AS, which could provide the base to properly understand the molecular mechanism related to the OsROS1a gene in the regulation of rice seed development.

Realization of long retention properties of quantum conductance through confining the oxygen vacancy diffusion

Quantum conductance, known as Sharvin point contact, has been extensively investigated in many electronic devices, including diodes, transistors, and switches, especially in conductive filaments-based memristors. Quantum conductance with one or multiple atoms point connection can overcome the limitations of scaling and operating speed of nonvolatile multiple memory, logic device, and brain-inspired computing systems. However, because of the instability of the atomic arrangement in the one/multiple atoms connection in a conductive filaments-based memristor, it is a great challenge to maintain quantum conductance states for a long time. Here, we demonstrate that the stable long-time retention of multi-level quantum conductance states can be realized in Mott insulator vanadium dioxide with a highly oriented crystalline texture. According to in situ transmission electron microscope, conductive atomic force microscope, and detailed energy band analysis results, it is proposed that the grain boundaries act as reservoirs for oxygen vacancies and confine the oxygen vacancy diffusion in the narrow grain boundaries due to the higher bulk diffusion barrier. Our approach is extremely crucial for realizing quantum conductance-based electronic devices, such as multi-level and high-density storage and neuromorphic computing.

Synthesis of WC-0.67wt.%Cr3C2 nanopowders by a one-step reduction-carbonization method and their characterization

Nano WC powders containing uniformly dispersed grain growth inhibitors are high-quality raw materials suitable for the fabrication of ultrafine grade WC-Co alloys. In this study, nano WC and WC-0.67wt.%Cr3C2 powders were prepared by a one-step reduction-carbonization method from WO3 and WO3-0.72wt.%Cr2O3 powders prepared via a spray drying-calcination process. The effect of Cr2O3 on the phase composition and microstructural evolution during the one-step reduction-carbonization of WO3 was investigated through X-ray diffraction, transmission electron microscopy, and scanning electron microscopy studies. When the reaction temperature was lower than 800 °C, WO2 and nano W phases were formed because Cr2O3 dispersed uniformly around the WO3 particles effectively hindered their reduction and inhibited the growth of W. With a further increase in the temperature to greater than 800 °C, Cr2O3 was gradually converted into Cr3C2 distributed on the surface of WC, leading to the formation of smaller WC grains. Additionally, Cr2O3 promoted the carbonation reaction due to the existent of smaller W with higher activity. Finally, the nano WC-0.67wt.%Cr3C2 powder with a narrow grain size distribution and high specific surface area of 4.58 m2/g−1 was obtained under a hydrogen gas flow rate of 50 L/min at 1100 °C in 0.5 h.

Effects of cryogenic deformation on the microstructure and mechanical properties of high-strength aluminum alloys

7A85 aluminum alloy forgings were compressed at 10% to 30% deformation at room and cryogenic temperatures, followed by solid-solution treatment, water quenching, 3% cold deformation, and two-stage aging. The results indicated that cryogenic deformation increased coarse second-phase particle fragmentation and led to massive dislocation proliferation, which facilitated particle dissolution due to the formation of more interfaces and dislocation-promoted dissolution. These increased the driving force for aging precipitation and produced denser matrix precipitates and narrower grain boundary precipitate-free zones. Meanwhile, numerous dislocations provided more nucleation sites for recrystallization and thus refined grains during solution treatment. The grains were refined from 500 μm in the undeformed state to an average size of 35 μm under 20% cryogenic deformation. The excessive dislocation energy and stored deformation energy at 30% deformation caused recrystallized grain growth. The optimal mechanical properties were obtained at 20% cryogenic deformation with an ultimate tensile strength, yield strength, and elongation of 499 MPa, 435 MPa, and 13.1%, which were respectively 1.6%, 2.1%, and 37.9% higher than those of the undeformed sample. • Uniformly fine equiaxed grains and the best elongation were obtained at 20% cryogenic deformation. • Excessive dislocation energy and stored deformation energy at 30% deformation led to recrystallized grain growth. • Increasing the deformation and decreasing the temperature resulted in denser matrix precipitates. • Increasing the deformation and decreasing the temperature resulted in narrower grain boundary PFZs.

Laser sintering of Al2O3‐based green ceramics prepared by different pre‐sintering temperatures

AbstractAl2O3‐based green ceramics are prepared by isostatic cold pressing technology. The prepared green ceramics are pre‐sintered at the temperature from room temperature to 1100°C, and then Al2O3 ceramics are prepared by laser sintering. The effects of pre‐sintering temperatures and laser parameters on mechanical properties and the sintering quality are analyzed. The results show that good crystallinity of Al2O3 particles is obtained at a higher pre‐sintering temperature. The flexural strength and density of green ceramics increase with the temperature of heat treatment. The flexural strength decreases slightly at ∼200°C due to the paraffin binder disintegration. The pre‐sintering temperature and laser processing parameters have a significant influence on the sintering quality. With the increase of laser power and laser frequency, dynamic grain growth occurs, and then grains are refined. The majority of plate‐like grains are transformed into long cylindrical‐like grains in the severe densification process. However, porous flocculation microstructures are generated on the samples pre‐sintered at 1100°C after laser sintering, which is due to the material gasification in atmospheric environment during sintering by infrared laser. More uniform microstructure and better sintering quality of samples pre‐sintered at 500°C can be achieved after laser sintering with a relatively narrower grain size distribution.

Preparation of nano-sized 6MgO–2Y2O3–ZrO2 powders by a combined co-precipitation and high energy ball milling process

Nanostructured ceramic materials doped with stabilizers have superior mechanical, chemical, and electrical properties. In this study, tetragonal zirconia stabilized by 6 mol% MgO and 2 mol% Y2O3 (t-6MgO–2Y2O3–ZrO2) nanopowders with quasi-spherical morphology, uniform particle size, and narrower grain size distributions were prepared by a combination process including two steps: namely co-precipitation and high-energy ball milling. The effect of ball milling time on ZrO2 crystal particles was investigated by characterizations including XRD, Raman, FT-IR, FEESM, BET, and TEM. With the increase of ball milling time, the average grain size of the powder showed a gradual decrease tendency, the particle size distribution changed from wide to narrow, the particle morphology tended to be spherical, and the specific surface area gradually increased. Under the optimized conditions (ball milling for 8 h, calcination temperature of 800 °C, and holding time of 2 h), the highly dispersed spherical nanopowders with a minimum particle size of 18.47 nm and an average particle size of 29.02 nm were obtained. These zirconium oxide nanopowders are suitable for the preparation of inorganic coatings, biomedical materials, catalyst materials, and other types of functional materials.

Crossover from intrinsic to extrinsic magneto transport in La1-xPbxMnO3 perovskite systems

The intrinsic to extrinsic magneto transport of Pb doping and intermediate grinding on transport as well as magnetic properties in La1-xPbxMnO3 (x = 0, 0.15, 0.25 and 0.4) has been investigated. Double exchange related electron transport is supposed to prevail in case of highly doped samples whereas spin dependent interfacial tunneling of conduction electrons along with double exchange related electron transport dominate conduction process in case of less Pb substituted samples. It has been shown that with repeated grinding and increase in doping percentage (within the doping limit), it is possible to have relatively narrow grain size distribution, which is a major cause of gradual disappearance of the intergrain interfacial tunneling (extrinsic) resistance leaving only intragrain (intrinsic) transport properties in the high temperature region. At low temperature the existence of spin-glass insulator behaviour were observed, which get stronger with decrease in Pb content. Thus with decrease in Pb doping, it has been possible to generate relatively wide distribution of grain size with probable increase in misorientation angle in the grain boundary region. This reveal a crossover from major intrinsic to combination of extrinsic, intrinsic magnetotransport and spin-glass behaviour.

The Dependence of Abnormal Grain Growth on Initial Grain Size in 316 L Stainless Steel

Abstract When 316 L stainless steel specimens are compressed to 30% and annealed at 1300 °C, primary recrystallization rapidly occurs and grains grow normally during further annealing treatment. Thus by annealing for various periods at 1300 °C, specimens with varying average sizes with identical normalized grain size distributions are obtained. When these specimens are heat-treated again at temperatures below 1150 °C, abnormal grain growth (AGG) occurs depending critically on the initial grain size.With decreasing initial grain size, AGG begins earlier during the heat-treatment, and if the initial grain size is large, only slow grain growth occurs without any distinct AGG for periods up to 48 and 96 h. It is observed that AGG occurs by faster growth of large grains with their velocities expected to increase nonlinearly with the driving force arising from the size difference. Because the AGG structure develops gradually, there is not really a well defined incubation time. With the same initial grain size the initiation ofAGGis slower at lower temperatures. A step heat-treatment experiment shows that if there are large grains embedded in the matrix of fine grains, they can grow abnormally under the condition where no AGG occurs with a narrow grain size distribution. The extremely slow grain growth with initially large average grain sizes is attributed to the low grain boundary velocity limited by the boundary step nucleation or growth. It is proposed that the same boundary step mechanism is qualitatively consistent with abnormal growth of the large grains with singular grain boundaries at low temperatures.