Random Distribution Of Grains Research Articles

Experimental study and numerical simulation of permanent magnet stirring on solidification of IN718 superalloy under different rotation speeds

A novel permanent magnet stirring (PMS) characterized by low power dissipation and high magnetic flux density provides an alternative method for producing IN718 superalloy with uniform microstructure during solidification. In the present work, the electromagnetic force and the molten superalloy flow of PMS under different rotation speeds (0, 75, 150, and 300 rpm) were calculated based on the multi-physics field analysis software Comsol and the flow field software Fluent. The calculated results were validated using the measured magnetic flux densities under different rotation speeds. It was found that the calculated maximum electromagnetic force enhanced from 2.73 to 10.78 kN/m3, and the maximum tangential velocity increased from 0.13 to 0.46 m/s in a diameter of 50 mm molten IN718 ingot when the rotation speeds increased from 75 to 300 rpm. Moreover, the experimental results revealed that the regions of solidification dendrites were broken under the impact of PMS, which were a source of refinement grains and attributed to the uniform distribution of Laves phase (average size decreased from 74.86 to 38.83 µm in the edge) during solidification. In addition, grain refinement and a random distribution of grains decreased texture intensity with the maximum value from 6.124 to 3.828.

Fast Statistical Homogenization Procedure for estimation of effective properties of Ceramic Matrix Composites (CMC) with random microstructure

The modern polycrystalline composite materials have a complex internal structure consisting of different phases and interfaces with random distribution. Relevant examples are Al2O3/ZrO2, i.e. alumina/zirconia composites, widely used as structural materials with applications ranging from aerospace to bio-engineering. Depending on the phases content and on the grain size a broad range of material characteristics, among which elastic constants, can be obtained.With the aim of characterizing this class of materials, we exploit a numerical Fast Statistical Homogenization Procedure (FSHP) in order to both estimate the size of the Representative Volume Elements (RVE) and the effective elastic properties, assuming a linear elastic material behaviour.The 2-D analyses are performed considering a microstructure inspired by images of real portions of the Al2O3/ZrO2 composite obtained from a scanning electron microscope. The recent Virtual Element Method is used in combination with the FSHP approach to numerically solve boundary value problems. Different volume contents of phases are considered ranging from pure Alumina to pure zirconia. The results are useful to reliably characterize such materials in the elastic range taking into account the role played by random distribution of grains.

Thin Films Characterization and Study of N749-Black Dye for Photovoltaic Applications

This paper reports on the fabrication and photovoltaic characteristics of a heterojunction solar cell based on an organic small molecular semiconductor, N-749 black dye (N749-BD). To investigate the photovoltaic characteristics of N749-BD, an ITO/PEDOT:PSS/N749-BD/Ag device is prepared by spin casting a 100 ± 5-nm thin film of N749-BD on the poly(3,4, ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) film, which acts as buffer/hole transport layer (HTL) and indium tin oxide (ITO) is employed as a transparent conducting substrate. Under standard testing conditions (STC), i.e., 25 °C, 1.5 AM global and 100 mW/cm2 irradiation, the photovoltaic parameters of the device, such as fill factor (FF) and power conversion efficiency (PCE), are found to be 0.65 and 3.8% ± 0.5%, respectively. Current-voltage (I–V) characteristics of the device are also studied in dark conditions to measure reverse saturation current (I0), series resistance at the interface, rectification ratio (RR), barrier height (ϕb) and ideality factor (n). Optical bandgaps (Eg) of N749-BD thin film are found by applying Tauc’s plot on its ultraviolet-visible (UV-Vis) spectrum, which are measured to be 1.68, 2.67, 3.52 and 4.16 eV. External quantum efficiency (EQE) measurements of the fabricated device are studied, which demonstrate large value of EQE ≈ 12.89%, with peak intensity at 626 nm. Bond dynamics and compositional analysis of N749-BD is carried out via Fourier transformed infrared (FTIR) spectroscopy. Morphology of the thin film of N749-BD on quartz glass are investigated via scanning electron microscopy (SEM) with in-situ energy dispersive X-ray (EDX) spectroscopy which exhibits random distribution of N749-BD grains across the surface with nearly uniform grain sizes and shapes. The larger values of FF, PCE and EQE of ITO/PEDOT:PSS/N749-BD/Ag device suggests the potential of N749-BD to be utilized in low cost, simple manufacturing process and high performance of solar cells.

Numerical simulation and parameter sensitivity analysis of multi-particle deposition behavior in HVAF spraying

Particle deposition behavior is critical to improve coating quality. Based on the Coupled Eulerian and Lagrangian (CEL) method, a three-dimensional multi-particle random deposition model was established, and grain inhomogeneity was introduced into the TC18 substrate. A polycrystalline model of the microstructure for the sprayed substrate was established by the Voronoi method. The evolution of the temperature, strain and stress fields during particle deposition was revealed, and the formation mechanism of pore defects was also analyzed. The results show that the overall strain of small particles is large, the core strain of large particles is small, and the edge strain is significant. The stress value near the large particles in the coating is large, while the stress at the edge of the coating is relatively small. The stress distribution of the TC18 substrate is similar to the uneven random geometric distribution of grains. On this basis, the response surface model of coating characteristics was established, the influence of process parameters on coating characteristics was analyzed, and the sensitivity of process parameters is determined. This research can provide a basis and guidance for engineering applications in related fields.

High-temperature deformation behavior and recrystallization mechanism of a near beta titanium alloy Ti-55511 in β phase region

Isothermal compression tests, electron backscatter diffraction (EBSD) observations and quantitative analysis were performed to investigate high-temperature deformation behavior and recrystallization mechanism of Ti-55511 alloy in β phase region. The stress-strain curves, calculated activation energy and microstructure characterization show that dynamic recovery (DRV) and dynamic recrystallization (DRX) are the main soften mechanisms. DRX becomes more significant with decreasing strain rate and increasing deformation temperature and true strain. Recrystallization grains are identified by calculated grain orientation spread (GOS). It is found that quantitative microstructural characteristics, such as DRX volume fraction and DRX grain size, are strongly dependent on process parameters. The discontinuous dynamic recrystallization (DDRX) by grain boundaries bulging and continuous dynamic recrystallization (CDRX) by progressive sub-grains rotation are observed in the deformed microstructure of Ti55511 alloy. The flow softening rate and kinetics exponent of DDRX are higher than those of CDRX. With increasing deformation temperature, DRX mechanism has transformed from DDRX to CDRX, resulting in the unexpected decrease of DRX kinetics exponent nD and flow softening rate. The ηbcc fiber, εbcc fiber and ξbcc fiber are the dominant texture component in deformed Ti–55511 alloy. The weakening of the deformation texture is accompanied by the occurrence of DRX, which can be attributed to the random orientation distribution of DRX grains.

Numerical analysis of rolling contact fatigue crack initiation Considering material microstructure

The material microstructure of plays an important role in crack initiation of rolling contact fatigue. To address crack initiation of tapered roller bearings, the inhomogeneous characteristic of material is considered. The random distribution of material grains is simulated with Voronoi graph, and a Voronoi finite element model of rolling contact fatigue is given. Numerical analysis of damage-life constitutive relation is carried out with finite element analysis. The effect of material microstructure inhomogeneity on initiation life of fatigue crack is studied. Researches show that the smaller the grain size, the more difficult the fatigue crack appearing. The larger the difference of elasticity modulus between non-metallic inclusions and matrix material, the greater the impact on fatigue life of crack initiation. The angular and sharp non-metallic inclusions reduce fatigue life more than rounded shape inclusions. Initiation life of fatigue crack has a minimum value on a critical depth of nonmetallic inclusion. The longer distance between two laterally arranged inclusions, the greater it affect the initiation life of fatigue crack. The effect of distance between two vertically arranged inclusions on fatigue crack initiate depends on the depth of inclusions.

A grinding force prediction model with random distribution of abrasive grains: considering material removal and undeformed chips

A grinding force prediction model with random distribution of abrasive grains: considering material removal and undeformed chips

Distribution of natural beta dose to individual grains in sediments

In luminescence dating using single grains of quartz, statistical protocols are used to compute the most appropriate dose from the distribution of palaeodoses. The distribution of palaeodoses arises due to, (1) heterogeneity (at grain level) in bleaching at the time of deposition, (2) heterogeneous distribution of beta emitters present as randomly distributed feldspars (Mayya et al. in Radiat Meas 41:1032–1039, 2006) and, (3) heterogeneous distribution of grainsizes (Guérin et al. in Radiat Meas 47:778–785, 2015). Mayya et al. (Radiat Meas 41:1032–1039, 2006) demonstrated that random distribution of feldspar grains(with up to 14% stoichiometric K) and shorter range of beta particles (~ 2.3 mm in quartz) lead to significant variation in dose received by individual grains of quartz. This study improves upon Mayya et al. (Radiat Meas 41:1032–1039, 2006) by, (1) using a more realistic energy deposition function that was estimated using Monte Carlo simulations and (2) computing the effects of porosity of the sediment and beta straggling on the dose distribution function. It additionally concludes that effects of beta straggling are small and can be ignored. Ages based on new calculations led to improved concordance with control ages.

Analyzing coarsening versus densification phenomenon present in partial sintering of Al2O3/TiO2 composites

Alumina–titania (Al2O3/TiO2) composites are well-known for their physical and microstructural properties, which allow several engineering applications. However, these properties change when different sintering temperatures are used, due to the existence of two antagonistic phenomena (grain coarsening versus densification) that occurs during sintering process. The aim of this study was to evaluate the microstructural and physical properties of the alumina–titania composites and to understand these two antagonistic phenomena when different partial sintering temperatures are used. The composites were prepared from alumina and titania powders by uniaxial pressing and sintered at different temperatures (1100–1400 °C). The structural analysis showed that in addition to expected phases (α-Al2O3 and rutile), the alumina–titania composite sintered at 1100 °C presents anatase phase, while those obtained at 1300 and 1400 °C present tialite phase. The morphology analysis revealed a random distribution of grains with irregularly shaped pores. According to the Archimedes-based immersion test, all composites have a relative bulk density ranging 60.43–73.59%, showing that none of them reached the final sintering stage. Statistical analysis revealed that the average grain size of the matrix ranges from 3.62 to 5.24 μm. Moreover, the statistical analysis also showed that the grain coarsening predominates over densification for the composites sintered from 1100 to 1150 °C. The densification predominates over grain coarsening for the composites sintered from 1150 to 1200 °C, and from 1250 to 1400 °C. The two phenomena coexist only for the composites sintered from 1200 to 1250 °C.

Cutting Performance of Randomly Distributed Active Abrasive Grains in Gear Honing Process.

In power gear honing, the random distribution of abrasive grains on the tooth surface of the honing wheel is the main factor that influences the machining performance of high-quality hardened gears. In order to investigate the micro-edge cutting performance of the active abrasive grains on the workpiece gear, the real honing process is simplified into a micro-edge cutting model with random distribution of active abrasive grains in the cells of the meshing area by obtaining the random distribution states such as the position, orientation and quantity of the honing wheel teeth. The results show that although the active abrasive grains are distributed at different locations, they all experience three types of material removal—slip rubbing, plowing and cutting—allowing the gear honing process to have the combined machining characteristics of grinding, lapping and polishing. The active abrasive grains in first contact produce high honing force, high material removal efficiency and poor surface roughness on the machined workpiece, while the latter ones have the opposite effects. The dislocation angle affects the chip shape and chip discharging direction, and the highest honing force and material removal efficiency is achieved with a dislocation angle of 135°. The higher the number of active abrasive grains in a given contact area, the higher the material removal efficiency.

INVESTIGATION ON THE ROCK CUTTING MECHANISM OF HETEROGENEOUS GRANITE USING A GRAIN-BASED MODELING APPROACH

A good understanding of rock cutting mechanism is of great importance for improving the cutting efficiency and reducing the costs in hard heterogeneous formation drilling. This paper implements the grain-based modeling approach to mimic the granite considering the highly heterogeneous mechanical behaviors of grains in granite. The rock cutting mechanism of granite, accounting for the influence of hydrostatic pressure, mineral size, random distribution, rake angle, cutting depth and velocity of cutter, are investigated. The research results demonstrate that the inter-grain shear crack and intra-grain tensile crack are the two main crack types generated during rock cutting process. The cutting force responses show strong vibration with respect to the cutting distance. The magnitude of cutting force sharply drops and abruptly rises during the cutting process, which becomes more obviously with the increasing hydrostatic pressure, cutting depth and rake angle of cutter. The hydrostatic pressure, grain size and random distribution of grains have great influence on chip morphology. In contrast, comparing with the above three factors, the cutting depth, rake angle of cutter and cutting velocity have little influence on the chip morphology. These results lead to an enhanced understanding of rock breaking mechanisms in granite, and provide a basis for improving the design of rock-breaking bits.

Prediction on nonlinear mechanical performance of random particulate composites by a statistical second-order reduced multiscale approach

A novel statistical second-order reduced multiscale (SSRM) approach is established for nonlinear composite materials with random distribution of grains. For these composites considered in this work, the complex microstructure of grains, including their shape, orientation, size, spatial distribution, volume fraction and so on, results in changing of the macroscopic mechanical properties. The first- and second-order unit cell functions based on two-scale asymptotic expressions are constructed at first. Then, the expected homogenized parameters are defined, and the nonlinear homogenization equation on global structure is established, successively. Further, an effective reduced model format for analyzing second-order nonlinear unit cell problem with less computation cost is introduced in detail. Finally, some numerical examples for the materials with varying distribution models are evaluated and compared with the data by theoretical models and experimental results. These examples illustrate that the proposed SSRM approaches are effective for predicting the macroscopic properties of the random composite materials and supply a potential application in actual engineering computation.

Surface roughness prediction model of GH4169 superalloy abrasive belt grinding based on multilayer perceptron(MLP)

GH4169 nickel-based alloy materials are widely used in the design of aero-engine compressor terminal stators and rotor blades because of their high strength, oxidation resistance and gas corrosion characteristics in high-temperature environments. In addition, the advantages of abrasive belt grinding in the processing of nickel-based alloy blades, such as low temperature and strong vibration absorption, can effectively improve the surface integrity and be popularized and applied by aviation manufacturers. However, due to the random distribution of abrasive grains, grinding heat and machining chatter during the abrasive belt grinding process, there is a coupling and strong nonlinear model relationship between the grinding process parameters and the surface roughness after grinding. At present, the strong nonlinear model relationship of multi-dimensional parameters and their coupling relationship has not been resolved, so it is difficult to achieve accurate prediction of surface roughness.We propose a study on the multi-dimensional parameter model of abrasive belt grinding for the decision-making of the surface integrity characteristics of nickel-based alloy blades. Based on the MLP multi-layer perceptron, a prediction model of abrasive belt grinding surface roughness is proposed. According to the multi-layer perceptron model and the input parameter characteristics of the belt grinding system, the initial connection weight and paranoia, the backward propagation algorithm, and the neural network layer are optimized. Through the above algorithm, a multi-dimensional parameter surface integrity nonlinear model is obtained and combined with boundary conditions to achieve accurate prediction of the surface roughness of nickel-based alloy abrasive belt grinding.

Investigation the micromechanisms of strain localization formation in AZ31 Mg alloy: A mesoscale 3D full-field crystal plasticity computational homogenization study

Wrought magnesium alloys exhibit strong basal texture after extrusion or rolling process. In this study, a numerically improved crystal plasticity finite element model in conjunction with computational homogenization has been used to investigate the micromechanism of strain localization in AZ31 Mg alloy under uniaxial tension along rolling direction (RD), uniaxial compressin along normal direction (ND) and biaxial tension in RD-TD plane. To this aim, the effect of texture and especially off-basal grains distribution on strain localization is elaborated in detail. Three realistic representative volume elements (RVE) of microstructure with 34, 60 and 58 grains and ≈578, ≈546and ≈1103 elements per grain have been synthetically constructed and analyzed to examine the effect of basal and off-basal grains distribution on the deformation patterns. Strongest strain localization was found in RVE. 1 where off-basal grains were arranged in a banded form. RVE. 2 with differing spatial position of off-basal grains showed weaker, yet discernible localized band. RVE. 3 with a nearly random distribution of off-basal grains depicted no clear side-by-side localized band. It was found that basal slip is the main contributor of compound strain localization regions. Moreover, high stresses inside the localized band can enforce well-oriented grains for non-basal slip located between off-basal grains to deform cooperatively. Upon the formation of localized bands, the remaining part of the RD-TD faces experienced insignificant deformation and clear deformation partitioning occurred. Regarding RD-ND faces, two distinct microscale localized zones have been observed. Basal and prismatic slip was the former of localized zones on the RD-ND faces.

Laser Application in Photovoltaics for Surface Texturization of Silicon and Front Electrode Deposition

Abstract The laser technology in the manufacturing of solar cells has become an indispensable element of modern photovoltaic technology. The main reason for taking up such research is because conventional methods used for monocrystalline silicon texturization are ineffective when applied to polycrystalline silicon texturing. This is related to random distribution of grains of different crystalographic orientations on the surface of polycrystalline silicon. Texturing a polycrystalline silicon surface using an Nd:YAG laser makes it possible to increase absorption of the incident solar radiation. The additional technological operation of etching in potassium hydroxide solution introduced into the technology of the photovoltaic cells manufactured from laser-textured wafers allows for improvement in electrical performance compared with cells produced from nontextured wafers. Moreover, this article presents the influence of selective laser sintering of front metallization that was manufactured using paste based on silver nanopowder on contact resistant. The electrodes were formed on monocrystalline silicon solar cells. The microstructures of laser-textured silicon and sintered front metallization were investigated by scanning electron microscope and confocal laser scanning microscope. The reflectance of produced textures was measured by spectrophotometer with an integrating sphere. Current-voltage characteristics of solar cells manufactured from laser-textured polycrystalline silicon wafer were measured under standard AM 1.5 radiation. The contact resistance between the metal and semiconductor was investigated using the transmission line model.

Investigation on the Hot Deformation Behavior of 316L Stainless Steel Using 3D Processing Map

Isothermal compression experiments have been adopted to systematically examine hot deformation behavior of 316L stainless steel on a simulator with 0.01–5 s−1 strain rate and 900–1100 °C temperature, and the results demonstrate that, in flow curves, both features of dynamic recrystallization (DRX) and dynamic recovery (DRV) can be observed. Besides, the constitutive model has been established, and the value of activation energy is obtained as 465.532 kJ mol−1. In addition, processing maps of different strains are also constructed. With microstructural observation, it can be found that the flow localization and mischcrystal structure occur while the hot deformation is performed on the instability domains (efficiency of power dissipation, $$ \eta $$, < 23%). The processing window is located at 0.01–0.056 s−1 strain rate and 1040–1100 °C temperature with the η higher than 35%. The optimal hot compression parameters are 1050 °C–0.01 s−1 with a peak efficiency of 38%, and the corresponding EBSD analysis shows a random distribution of DRX grains.

Anodic and cathodic deposition of polyaniline films: a comparison between the two methods

This paper reports the comparison of polyaniline (PAni) thin films grown by anodic and cathodic electrodeposition. The growth condition, structure, optical property, thickness and morphology of the deposited layers have been characterized using cyclic voltammogram, x-ray diffraction (XRD), UV–vis spectroscopy, optical profilometry and scanning electron microscopy (SEM). The thin films grown from anodic deposition show blue-violet colour, which denotes pernigraniline fully oxidised state whereas the layers grown using cathodic deposition show pale yellow colour, which indicates leucoemeraldine fully reduced state of PAni. PAni grown from anodic deposition exhibit amorphous phase with cementing effect growth and bandgap varies from 3.90–4.08 eV. PAni layer from cathodic deposition demonstrated crystalinity based on the presence of the two XRD peaks at 2θ = 30.7° and 32.1° in the XRD pattern with random distribution of smaller grains and bandgaps in a range from 1.05 to 1.20 eV. The properties of PAni thin films electrodeposited from anodic and cathodic deposition and under a variety of deposition conditions have been compared and discussed in detail.

Modeling and simulation of high-speed cylindrical grinding based on 3D grinding wheel topography

The purpose of this paper is to establish a 3D virtual grinding wheel to illustrate the high-speed cylindrical grinding process of difficult-to-machine materials under various process parameters. Based on Monte Carlo method, the abrasive grain is modeled cutting spherical solid with random planes, and the random distribution of grains is obtained based on the virtual grid method. Then the grinding wheel topography is trimmed to adjust the protrusion height of abrasive grains. The simulations of high-speed cylindrical grinding under different grinding conditions are carried out considering the thermomechanical coupling effect of grinding wheel and workpiece. The 3D grinding wheel is validated by analyzing the grinding force ratio. The effects of cutting depth on the grinding performance, such as grinding force, workpiece temperature, effective stress and surface quality, are discussed. The results show that a smaller depth of grinding is beneficial for better surface quality.

Micromagnetic simulation of the effect of grain boundaries and secondary phases on the magnetic properties and recoil loops of hot-deformed NdFeB magnets

Abstract Hot-deformed NdFeB magnets have attracted considerable attention due to their high thermal stability and exceptional corrosion resistance. In this study, the dependence of magnetic properties and recoil loops on the presence of a grain boundary phase (GBP) and Nd-rich secondary phases in hot-deformed NdFeB magnets was explored using micromagnetic simulations. By adjusting the parameters of the simulation model, the influence of several factors (thickness and spontaneous magnetization (Ms) of the GBP, Ms, total volume fraction and spatial distribution of the secondary phase), on the main and recoil loops was investigated. A change in thickness and in Ms of the GBP affects the coercivity (Hc) and remanence of the main loop. In particular, an increase of Ms leads to a decrease in the magnet’s Hc. The influence of the secondary phase depends on its spatial distribution. Large volume grains result in lower Hc, but the role in decreasing Hc is weaker in contrast to a random distribution of smaller grains of the same overall volume content. Open recoil loops were interpreted by analyzing the distribution of calculated magnetic moments and energy terms. Loop opening is not directly related to Hc of the main loop. Rather it is mainly due to small irreversibilities in the dipolar energy of different magnetic configurations that appear along the recoil loop.

Controlling self-organized criticality of a preferential sandpile model on scale-free networks

Controlling of self-organized criticality is attempted developing a two-state sandpile model on scale-free networks distributing sand grains to preferred nodes. Keeping the degree of one of the nodes fixed to the lowest possible value and varying the degree of the other node from the lowest to the highest possible value, the critical steady state of the model is characterized for a wide range of degree distribution for a given dissipation rate. The preferential sand distribution to the targeted nodes leads to completely different dynamics and toppling number density correlation in comparison to random distribution of sand grains as in a stochastic model. The model is found to follow the mean-field theory in the random regime, whereas a nontrivial scaling behaviour very different from the mean-field one is observed in the scale-free regime of the network. Distribution of sand grains to the extreme degrees is found to be an efficient and cost-effective way of controlling self-organization as the catastrophic cascades in terms of large avalanches in this model are found to be confined in certain restricted regions of the network in the scale-free regime contrary to that of a stochastic model where the whole network gets exposed.