Uniform Grain Size Research Articles

Evolution of Recrystallized Grain and Texture of Cold-Drawn Pure Mg Wire and Their Effect on Mechanical Properties.

Static recrystallization plays a key role in the fabrication of thin Mg wires as well as the mechanical properties of the final wires. The effect of annealing parameters on the evolution of the microstructures, textures and mechanical properties of cold-drawn pure Mg wire was studied by means of optical microscopy (OM), electron backscatter diffraction (EBSD), a tensile test and a hardness test. This study shows that the mechanical properties of as-annealed pure thin Mg wire is affected not only by the average grain size, but also the uniformity of the recrystallization grains, including the uniformity of grain size and crystal orientation distribution (more random texture component). With increasing annealing temperature and time, the uniformity of recrystallization grain size first improved and then declined after obvious grain growth. At the same time, the randomness of the basal texture component declined with the development of recrystallization. Annealing at 300 °C for 30 min caused the most uniform grain size and orientation distribution in the microstructures, thus contributing to the best plasticity among all experimental wires. It is reasonable to conclude that more uniform and regular recrystallized grains and a more randomly distributed crystal orientation would be benefit for the mechanical properties of Mg wires.

Evaluation of Uncertainty in Determining Average Grain Size by ASTM E112 Standard

In this paper, the ASTM grain size number of aluminium alloy specimen was determined respectively by Abrams Three-Circle Procedure and Planimetric Procedure of ASTM E112-13 Standard, and the uncertainty of the result was evaluated. The results are as follows: 1) Using the Abrams Three-Circle Procedure determines G, G=4.13, U=0.26, k=2; Using the Planimetric Procedure determines G, G=3.94, U=0.15, k=2. 2) It is suggested that the ASTM E112 standard should provide that the errors of counting grain boundary intersection count or number of grains should be less than or equal to 2, and the ruler that determines the diameter of test circle or scale length should be with the scale that is less than or equal to 0.10 mm. On this condition, the uncertainties caused by them in determining G can be negligible. 3) The main sources of uncertainty for the determination of G by Abrams Three-Circle Procedure and Planimetric Procedure are repetitive measurement, which depends on the uniformity of grain size of specimen. 4) The %RA limit of ASTM E112 for determining G should be redefined according to the measurement uncertainty in order to be up to the precision requirement (±0.25).

A study on the nucleation and MPCVD growth of thin, dense, and contiguous nanocrystalline diamond films on bare and Si3N4-coated N-polar GaN

We report upon the microwave plasma chemical vapor deposition (MPCVD) growth of polycrystalline diamond on varying crystallographic orientations of GaN (Ga-polar and N-polar), as well as on Si3N4-coated N-polar GaN, as applied to top-side heat spreading layers for III-N-based high electron mobility transistors. Integration of diamond with GaN in this configuration is subject to differing process constraints from previous research focusing on backside heat sinks. A critical requirement is to prevent hydrogen-related etching of the III-N surface in the H+ plasma ambient, as well as to avoid plasma damage to the GaN crystal or HEMT channel region near the surface. Thus we developed the seeding and MPCVD techniques under a low power density plasma with low sample temperatures during deposition. We systematically investigated samples seeded via polymer-assisted dip seeding in a nanoparticle suspension, which were then subjected to MPCVD growth under identical conditions. We evaluated the quality of the films via scanning electron microscopy and Raman spectroscopy to understand the relationship between grain size, interface abruptness, propensity for surface etching, as well as film uniformity. Finally, we were able to identify a process window for both N-polar GaN and Si3N4-coated N-polar GaN which yields thin, fully coalesced, nanocrystalline diamond films with an abrupt interface to the underlying substrate. These diamond films exhibit microscopic uniformity in crystal grain size, and macroscopic uniformity in thickness and interface abruptness via a process which is scalable to large wafer sizes.

Barrier lake formation due to landslide impacting a river: A numerical study using a double layer-averaged two-phase flow model

A granular landslide impacting a river may lead to the formation of a landslide dam blocking the streamflow, and subsequently create a barrier lake. Should a barrier lake outburst, the flood may be destructive and spell disastrous consequences downstream. The last decade or so has witnessed a number of experimental and numerical investigations on barrier lake outburst flooding, whilst studies on barrier lake formation remain rare – a physically enhanced and practically viable mathematical model is still missing. Generally, barrier lake formation is characterized by multi-physical, interactive processes between water flow, multi-sized sediment transport and morphological evolution. Here, a new double layer-averaged two-phase flow model is proposed, which is an advance on existing continuum models that involve a single-phase flow assumption and presume a single sediment size, and discrete models that preclude fine grains and assume narrow grain size distributions. The proposed model is first validated against data from previous laboratory experiments of waves due to landslides impacting reservoirs and landslide dam formation over dry valleys. Then it is applied to explore the complicated mechanism and threshold for barrier lake formation. The water and grain velocities are shown to be disparate, characterizing the primary role of grains in driving water movement during subaqueous landslide motion and also demonstrating the need for a two-phase flow approach. The grain size effects are revealed, i.e., coarse grains and grain-size uniformity favour barrier lake formation. A new threshold condition is proposed for barrier lake formation, integrating the landslide-to-river momentum ratio and grain size effects. The present work facilitates a promising modelling framework for solving barrier lake formation, thereby underpinning the assessment of flood hazards due to barrier lakes.

Estimation of flow stress and grain size uniformity of nickel alloy steel for the heavy plate rolling process

Artificial Neural Networks (ANN) is considered one of the most practical technologies in the fields of intelligent engineering and manufacturing. In the hot rolling process of visco-plastic characteristics, the ANN can be applied not only for improving the machining accuracy but also for relaxing the experimental constraints to analyze the critical data such as flow stress for a precise control. With this points, the ANN allows materials with non-linear properties and high strength such as nickel alloy steel to be machined in a wide range of temperature and dimension because the force and torque prediction of rolling process can be stable. In this study, the accuracy estimation between constitutive calculation based on Arrhenius type equation and multi-layer ANN for the nickel alloy steel rolling process is carried out. The flow stress prediction error by constitutive calculation could not represent the nonlinear characteristics of nickel alloy materials because the calculation method includes the average concept of rate of change for influence factors such as α, n, lnA, activation energy Q. But the ANN of backpropagation could be applied to improve the prediction accuracy over the nonlinear tendency of flow stress. The reliability of flow stress prediction by the ANN of multilayer type is verified by checking the nonlinear characteristics of nickel alloy steel rolling process with the Karman and Orowan’s theory. It is found that the standard deviation of flow stress is within 2.7%. It is also found that the ANN method could be applied to plate rolling process with a high accuracy of flow stress prediction of 3.5%. Finally, a higher uniformity of grain size could be obtained through the multi-pass rolling size than that by the forging process.

Microwave sintering of 316L stainless steel: Influence of sintering temperature and time

This study deals about the influence of sintering temperature and holding time on microwave sintered PM stainless steel 316L microstructure, hardness and self-limiting characteristics. The samples exhibited increasing theoretical density upon increase in sintering temperature and superior density of 89.77% theoretical achieved at 1300 °C of 60 min holding time. Grain size distribution of microwave sintered SS316L at three different sintering temperatures (1200 °C, 1250 °C and 1300 °C) was compared, almost 68% to 75% uniformity in grain size was noticed and the largest grain (115 µm) was observed at 1300 °C with 60 min holding time. Self-limiting characteristics of microwave absorption analysed by time-temperature graph at different sintering temperatures. The effect of soaking time influenced the grain size, i.e., higher the soaking time larger the grain size. After maximum microwave absorption in core region, from outer surface region SiC susceptor play a role in contributing heat (20 °C/min) at the temperature beyond 1130 °C to achieve maximum sintering temperature.

Microstructure and Mechanical Properties of Adding Adhesive-Layer Laser-Welded Joints of DP590 Dual-Phase Steel and 6061 Aluminum Alloy

In this study, the experiments of laser weld bonding for DP590 dual-phase steel and 6061 aluminum alloy were carried out. Plasma shape and welding spectra were collected and analyzed, and the effect of adding adhesive layer on the microstructure and mechanical properties of laser-welded joints was also investigated. Some defects, such as pore, crack and softening in heat-affected zone, can be avoided in the weld, the increased weld penetration and width are obtained by adding adhesive layer, and the average tensile–shear strength of joint exceeds than that of no-added joint. In laser weld bonding, the Al content reduces weld penetration depth, but increases both sides of weld, Fe-rich Fe–Al ICMs with better ductility are formed in steel/aluminum interface, the Al diffusion from the lower aluminum to the upper steel side is suppressed, and transverse area of joining steel to aluminum is increased due to increasing Al volume fraction on weld width. In addition, the uniform-sized grains are distributed in the weld, shear load is shared by adhesive layer and weld, and hence, mechanical properties of laser-welded joints are improved.

Effect of copper surface morphology on grain size uniformity of graphene grown by chemical vapor deposition

The graphene grain boundaries (GGBs) of polycrystalline graphene grown by chemical vapor deposition (CVD) typically constitute a major reason of deterioration of the electrical properties of graphene-based devices. To reduce the density of GGB by increasing the grain size, CVD growth conditions with a reduced CH4 flow rate have been widely applied and, recently, electropolishing of copper (Cu) foil substrates to flatten the surface has been undertaken prior to graphene growth. In this study, we show that polycrystalline graphene layer grown on typical Cu foil features two heterogeneous regions with different average grain sizes: small-grain regions (SGRs) and large-grain regions (LGRs). Statistical analysis of the grains of the graphene layers grown under different process conditions showed that SGRs (which form on Cu striations) limit the average grain size, the ability to control the grain size through adjustment of growth conditions, and global grain-size uniformity. Analysis showed that the surface-flattening process significantly improves grain-size uniformity, and monolayer coverage, as well as the average grain size. These results suggest that a process for flattening the surfaces of Cu substrates is critical to controlling the quality and uniformity of CVD-grown graphene layers for practical device applications.

Aqueous gelcasting of solid-state-sintered SiC ceramics with the addition of the copolymer of isobutylene and maleic anhydride

As a nontoxic and eco-friendly gelling agent, the copolymer of isobutylene and maleic anhydride (PIBM) was successfully used for aqueous gelcasting of dense solid-state-sintered SiC (S-SiC) ceramics. We acquired low-viscosity SiC-B4C-C slurry with an ultrahigh solid loading of 55 vol% through a synergy strategy of surface modification and particle grading of fine (D50 =˜ 0.5 μm) and coarse (D50 = ˜4.6 μm) SiC powders. With the addition of a low amount (0.3 wt%) of PIBM, the slurries were in-situ solidified to form green bodies after kept 2 h at room temperature. Gelcasted S-SiC ceramics were sintered at 2160 °C and densified with relative densities of ≥95.9%. The sintered bulks possessed fine equiaxed grains of uniform size owing to the pinning effect of coarse SiC particles, and presented a moderate flexure strength of 291 ± 8 MPa and a high fracture toughness of 4.55 ± 0.46MPam1/2.

High-efficiency synthesis of high-performance K0.5Na0.5NbO3 ceramics

Pure (K0.5Na0.5)NbO3 (KNN) ceramics with high density, fine and uniform-size grains were prepared by mechanochemical activation-assisted process. The time of synthesis is only 100 min, which is 72% – 93% shorter than the 6–24 h of the conventional solid-state method. Compared to samples prepared by conventional solid-state method, both the microstructure evolvement and electric properties were explored in detail. Results show the electric properties was significantly improved. Moreover, the dielectric and ferroelectric properties of obtained KNN ceramics exhibit strong dependence on the crystal size of the initial powders. The optimized ceramics HKNN100 showed a quite high energy storage performance, i.e., large electric energy storage density (Wtol = 1.612 J/cm3) and recoverable energy storage density (Wrec = 0.431 J/cm3), which can be mainly ascribed to the large dielectric breakdown strength (DBS = 110 kV/cm). Our works demonstrated that mechanochemical activation-assisted method possesses advantages for high-efficiency preparation of KNN or KNN-based ceramics.

Impact of calcium doping on structure, catalytic and conductive properties of lanthanum strontium iron oxide

A set of dense structure materials based on La0.5Sr0.5-xCaxFeO3 with different amount of calcium (where x varies from 0 to 0.1) were prepared. It was found that with calcium addition the hexagonal perovskite La0.5Sr0.5FeO3 structure is preserved and Ca2+ ions accommodate themselves easily in the lattice. The sintered ceramics have homogeneous microstructure and uniform grain size distribution with the average size which increases with Ca addition. Electrical properties of the sintered materials determined by the DC method revealed an increase in sample conductivity with Ca2+ doping. An increase in structure stability with the increase of calcium addition was also confirmed by the temperature-programmed studies.

CFD-DEM simulation of drying of food grains with particle shrinkage

Food grains naturally undergo physical and structural changes during a drying process. The volumetric change of particles or particle shrinkage is one of the important and complicated physical changes in drying. In this work, a shrinkage model for particle diameter reduction is incorporated into the computational fluid dynamics- discrete element method (CFD-DEM) drying model for food grains. First, mixing, general drying and shrinkage characteristics including particle and air moisture content, and particle diameter variation are reproduced. Then, the model is tested by comparing the predicted moisture reduction and volume shrinkage curve with the experimental data of wheat from the literature. The results demonstrate the capability of the current model in predicting drying and particle shrinkage characteristics. Finally, the effects of inlet air temperature and velocity on drying and particle shrinkage are studied. It is revealed that the shrinkage rate increases significantly with increasing air temperature but increases slightly with increasing inlet air velocity. The uniformity of grain size, quantified here by the standard deviation of the particle diameter distribution, increases with decreasing air temperature or increasing air velocity. This grain scale drying model with particle shrinkage should be useful for the design and control of many drying processes.

Tribological Behavior of Pulsed Electrodeposited Ni-W/SiC Nanocomposites

Ni-14 at.% W/SiC nanocomposite coatings containing 0-6 vol.% of submicron size (0.35 μm) SiC particles were obtained using pulsed electrodeposition technique on mild steel substrate. The coatings were subsequently characterized for uniformity of SiC distribution, grain size and mechanical properties (hardness and elastic modulus) using SEM, XRD and nanoindentation techniques, respectively. It was observed that the SiC particulates were uniformly distributed within the coating. The coating matrix (Ni-W) also exhibited nanograin size. Tribological behavior of Ni-14 W/SiC nanocomposite was analyzed under dry sliding wear test conditions using pin on disk method. The interrelationship between SiC content, interparticle spacing, mechanical properties and wear behavior was analyzed. The results suggest that whereas hardness and modulus of nanocomposite coatings varied with SiC content as per Rule of Mixtures, wear mechanism can be best explained on the basis of Inverse Rule of Mixtures.

Effect of extrusion speeds on the microstructure, texture and mechanical properties of high-speed extrudable Mg[sbnd]Zn[sbnd]Sn[sbnd]Mn[sbnd]Ca alloy

A new type of low-cost Mg-3.36Zn-1.06Sn-0.33Mn-0.27Ca (wt.%) (named as ZTMX3100) alloy ingot with good extrudability was prepared by semi-continuous casting. Two-stage homogenization treatment and hot extrusion were performed on the ingot. The effects of extrusion speeds (0.2–10 mm/s) on the extrudability, microstructure and mechanical properties of the alloy were investigated. The excellent extrudability of the alloy is attributed to the high incipient melting temperature of 572 °C resulting from the formation of thermally stable phase CaMgSn. CaMgSn phases distribute along the extrusion direction at each extrusion speed. The average grain size increases gradually and distribution uniformity of grain size firstly increases and then decreases. The as-extruded alloys exhibit textures with (0001) basal planes parallel to extrusion direction. Besides, the alloy exhibits a <101¯0> or <101¯0> − <112¯0> fiber texture depending on extrusion speed. The alloy extruded at 0.2 mm/s presents the highest mechanical property, which is attributed to the fine grain structure, strengthening effect from second phase particles, and weak basal texture. The alloy extruded at high speed of 10 mm/s (die-exit speed 18 m/min) still maintains a relatively high strength and elongation, which is mainly due to the combined effect of moderate alloying content and thermally stable phase CaMgSn.

Finite element modeling of grain size effects on the ultrasonic microstructural noise backscattering in polycrystalline materials

The correlation between ultrasonic wave propagation and polycrystalline microstructures has significant implications in nondestructive evaluation. An original numerical approach using the finite element method to quantify in both time and frequency domains the ultrasonic noise scattering due to the elastic heterogeneity of polycrystalline microstructures is presented. Based on the reciprocity theorem, it allows the scattering evaluation using mechanical data recorded only on the boundary of polycrystal instead of within its volume and is applicable to any polycrystalline aggregate regardless of its crystallographic or morphological characteristics. Consequently it gives a more realistic and accurate access of polycrystalline microstructures than the classical analytical models developed under the assumption of single scattering and the Born approximation.The numerical approach is proposed within the same unified theoretical framework as the classical analytical models, so it is possible to validate it in the cases of idealized microstructures for which the considered analytical models remain relevant. As an original result, assuming single phase, untextured and equiaxed microstructures, two-dimensional (2D) theoretical formulas are developed and a frequency-dependent coefficient is found compared to the classical three-dimensional (3D) formulas. 2D numerical simulations are then performed for idealized microstructures composed of hexagonal grains with a uniform grain-size. Three grain sizes are considered herein and involve different scattering regions. Good comparisons are obtained between theoretical and numerical estimates of the backscattering coefficient, which validate the numerical approach. Effects of the grain boundary orientations are analyzed by modeling an irregular hexagonal grain morphology and a random grain morphology generated by an established Voronoi approach. The origin of the significant oscillation level of backscattering is then investigated and discussed.

Solvent-modulated reaction between mesoporous PbI2 film and CH3NH3I for enhancement of photovoltaic performances of perovskite solar cells

Solvent engineering with dimethylsulfoxide (DMSO) has been shown to achieve high quality methylammonium lead iodide (MAPbI3) films for high performance perovskite solar cells (PSC). The morphology and composition of the intermediate PbI2-DMSO films play the key role for the success. The coordination and crystal growth of the PbI2–DMSO film however remain un-exploited. We study the way and extent of DMSO coordination and subsequent crystal growth of the PbI2-DMSO film to fabricate high quality perovskite films for enhancement of the photovoltaic performances of the cells. The DMSO is pre-coordinated or coordinated in-situ with PbI2 at a 1:1 or 2:1 M ratio. The PbI2-DMSO film from pre-coordination at 1:1 M ratio gives perovskite films of the best quality, being dense and possessing uniform size grains, high light absorption, and long charge carrier life times, among all investigated. The champion PSC achieves a high power conversion efficiency of 15.2%, significantly outperforming 13.0% of PSC based on PbI2-DMSO films from in-situ coordination at 1:1 M ratio, and 11.7% of PSC based on plain PbI2 films.

Influence of Warm Deformation on Strain-Induced Martensite Behavior of 316L Stainless Steel

In order to control the ratio of nano/ultrafine structure grains of warm/cold rolled 316L stainless steel after annealing, the influence of deformation amount and temperature on martensite content and microstructure was investigated, and a model of the content of stain-induced martensite and deformation amount and temperature was established. Results showed that the content of stain-induced martensite was nonlinear with deformation amount, but with an incubation period. And it’s generally exponential. Martensitic transition occurred in large deformation stage. 58.23% strain-induced martensite was formed when deformation amount was 80% at 200°C. The content of martensite is the most significant factor that affects austenite grain size after annealing. With more strain-induced martensite, the average austenite grain size decreased, and the uniformity of grain size was improved, which was generally monotonous.

Crop structure in winter oats and the effect of nitrogen on quality-related characters

ABSTRACTThe relationship between panicle structure and oat grain quality characteristics was examined in a winter oat (Avena sativa) experiment, cv. Gerald, fertilized with 80 and 200 kg/ha N. Spikelets on each whorl were counted and separated into primary, secondary, and tertiary grains, which were counted and weighed, and the kernels extracted manually and weighed. Tiller and whorl rank had relatively small effects on weight per grain and kernel content. Nitrogen application significantly increased weight per primary and secondary grain on the main stem and T1, the first tiller, while spikelet and grain numbers increased only on T1. However, weight per grain and kernel contents in all whorls on both the main stem and T1 were not significantly affected by nitrogen. Although kernel contents were significantly affected by nitrogen application on some occasions, increases and decreases were less than 2.5%. Across the whole plant, numbers of primary and secondary grains increased at the higher nitrogen application, but weight per primary grain and kernel contents were unaffected. However, weight per secondary grain significantly increased at the higher nitrogen application, thus improving uniformity of grain size which is of value to millers.

Morphological reactions of schematic alluvial rivers: Long simulations with a 0-D model

The paper presents a 0-D model of an alluvial watercourse schematized in two connected reaches, evolving at the long time-scale and under the hypothesis of Local Uniform Flow. Each reach is defined by its geometry (constant length and width, time-changing slope) and grain-size composition of the bed, while the sediment transport is computed using a sediment rating curve. The slope evolution is provided by a 0-D mass balance and the evolution of the bed composition is computed by a 0-D Hirano equation. A system of differential equations, solved with a predictor-corrector scheme, is derived and applied to the schematic watercourse to simulate the morphological response to changing initial conditions, and the evolution towards long-term equilibrium conditions. Differently from a single-reach 0-D schematization with uniform grain-size, besides the simplifications adopted, the model proposed here simulates the behaviour of alluvial rivers in a physically-based way, showing a grain-size fining in the downstream direction accompanied by milder slopes, and a tendency to develop concave longitudinal profiles.

Using an Atmospheric Pressure Chemical Vapor Deposition Process for the Development of V2O5 as an Electrochromic Material

Vanadium pentoxide coatings were grown by atmospheric pressure chemical vapor deposition varying the gas precursor ratio (vanadium (IV) chloride:water) and the substrate temperature. All samples were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, cyclic voltammetry, and transmittance measurements. The water flow rate was found to affect the crystallinity and the morphological characteristics of vanadium pentoxide. Dense stacks of long grains of crystalline oxide are formed at the highest amount of water utilized for a substrate temperature of 450 °C. Accordingly, it was indicated that for higher temperatures and a constant gas precursor ratio of 1:7, the surface morphology becomes flattened, and columnar grains of uniform size and shape are indicated, keeping the high crystalline quality of the material. Hence, it was possible to define a frame of operating parameters wherein single-phase vanadium pentoxide may be reliably expected, including a gas precursor ratio of 1:7 with a substrate temperature of &gt;450 °C. The as-grown vanadium pentoxide at 550 °C for a gas precursor ratio of 1:7 presented the best electrochemical performance, including a diffusion coefficient of 9.19 × 10−11 cm2·s−1, a charge density of 3.1 mC·cm−2, and a coloration efficiency of 336 cm2·C−1. One may then say that this route can be important for the growth of large-scale electrodes with good performance for electrochromic devices.