3D Grain Research Articles

Laser sharpening evaluation of diamond wheels based on 3D recognition

A modified U-Net neural network was used to evaluate the laser sharpening quality of diamond grinding wheels, and the laser sharpening parameters were optimized. The three-dimensional (3D) detection algorithm is researched, and a 3D detection algorithm for the diamond wheel surface matching the two-dimensional (2D) image and the 3D point cloud was proposed. The recognized 2D grain image is filtered to remove edge grains and connected grains, correct the 3D point cloud by eliminating the effect of curvature, and match grain pixels. The laser sharpening experiment of the bronze-bonded diamond wheel was carried out by the orthogonal experiment method, and the quality evaluation of the laser sharpening pictures of the wheel obtained by the experiment was carried out. The embedding depth of the abrasive grains was obtained from the 2D area of the abrasive grains, and the evaluation index of abrasive grain height-depth distribution was proposed. The laser sharpening experiments was carried out to obtain grinding wheels with different sharpening qualities, and the grinding tests were carried out. The effectiveness of the sharpening evaluation index was verified by the amount of grinding force when grinding the workpiece and the surface roughness of the workpiece after grinding. The optimal dressing process parameters were obtained as the average power of 35 W, the repetition frequency of 100 kHz, the rotational speed of 300 r/min, and the scanning speed of 3.6 mm/min.

Effect of charge compensation change on the crystal structure, grain growth behavior, and dielectric properties in the La2O3-doped BaTiO3 system with MnCO3 addition

The effect of MnCO 3 additions on crystal structure, grain growth behavior, and dielectric properties were studied in the La 2 O 3 -doped BaTiO 3 system. La 2 O 3 -doped BaTiO 3 powders were prepared by conventional solid-state reaction routes and then after the addition of MnCO 3 , the powder compacts were sintered at 1250 ℃ in air. The tetragonality (c/a) of the samples increased with the amount of up to 0.5 mol% MnCO 3 and then decreased above 0.5 mol%. The 3D grain shape became more spherical polygons with increasing amounts of MnCO 3 . The grain growth behavior changed from suppressed growth to abnormal grain growth and finally normal grain growth with increasing amounts of MnCO 3 when the powder compacts were sintered. The correlation between the grain growth behavior and the grain shape change is discussed from the perspective of two-dimensional nucleation grain growth theory. Further, the dielectric properties are discussed in terms of the crystal structure, microstructural control, and charge compensation. • Grain growth behavior and crystal structure were investigated in La-doped BaTiO 3 with added MnCO 3 . • The tetragonality changed depending on the formation of oxygen vacancies and Ti-site replacement. • The grains of the sintered samples changed to a more spherical shape with the addition of MnCO 3 . • The critical driving force for growth steadily decreased with an increasing amount of MnCO 3 . • The dielectric properties could be controlled by altering the microstructure, tetragonality, and charge compensation.

Relating the kinetics of grain-boundary complexion transitions and abnormal grain growth: A Monte Carlo time-temperature-transformation approach

Grain boundaries undergo thermally-activated, first-order transitions that result in discontinuous changes of interfacial properties. Importantly, grain boundary transitions lead to changes in bulk material properties (e.g., embrittlement) and/or behavior (e.g., abnormal grain growth). Numerous studies have been completed on the equilibrium states of grain boundaries and their transitions (i.e., complexion transitions), but there have been far fewer investigations of complexion transition kinetics; complexion transitions occur on the atomic-scale and are therefore challenging to detect experimentally. In this work, a 3D Potts grain growth model with stochastic complexion transitions was employed to investigate complexion transition kinetics. A Johnson-Mehl-Avrami-Kolmogorov (i.e., JMAK) approach was used to extract nucleation and growth rates (i.e., transformation rates), while point process analyses and correlation functions were used to infer complex interrelated nucleation and growth events. Time-temperature-transformation (TTT) diagrams, in particular grain-boundary complexion, transformed grain, and abnormal grain TTT diagrams, were constructed to summarize the progress of complexion-related transformations. Such diagrams relate complexion-induced grain growth to the underlying complexion transitions and, in the case of abnormal grain growth (AGG), permit one to assess the role of AGG as a temperature-dependent, time-displaced indicator of complexion transitions. Overall, this work details a theoretical framework that can be used to better understand complexion transition kinetics as well as to develop tools for the design of bulk microstructures.

A statistical approach to determine data requirements for part porosity characterization in laser powder bed fusion additive manufacturing

A major factor in determining the fatigue life of fracture-critical parts is the effect of process-induced porosity. Prediction of critical pore size in different process regimes of a laser powder bed fusion (L-PBF) processed part could provide invaluable information for process development and qualification and certification efforts. However, the amount of data required to accurately populate the pore size distribution to predict the critical pore size is still unknown. To address this gap, the present study utilizes extreme value statistics to determine the data required to characterize porosity in the L-PBF additively manufactured parts fabricated using different processing conditions. 2D cross-sectional porosity data obtained via optical microscopy was used as an example to demonstrate the statistical modeling approach. The statistical modeling described here can also be applied to other manufacturing processes and other types of data such as 3D porosity measurements, grain size, and inclusions.

A generalized 3DLS-DEM scheme for grain breakage

We introduce a new generalized 3DLS-DEM (3D Level Set Discrete Element Method) scheme that incorporates grain breakage, taking an important step towards realistic modeling at the micro-scale with DEM. For the first time, simulating thousands of real 3D grains that are able to break, which was possible due to the algorithm used for grain breakage. The presented scheme is not only capable of efficiently simulating grains with real shapes but also preserving mass and grains morphology with high fidelity when breakage occurs. Hence, with this approach, further works within the original 3DLS-DEM scheme could take into account other physical phenomena at the grain-scale such as electrostatic induced cohesion, heat transfer, or the presence of a fluid, etc. On the other hand, the breakage process modified grain size and roundness distributions, which, in turn, might change the strength and critical state of the sample. Withal, the overall process seems to suggest that grain breakage may be a sufficient condition to exacerbate the prevalence of shear banding within the sample. Finally, our model is able to perform breakage on several real 3D grains of a sample consisting of thousands of grains in a generalized 3DLS-DEM scheme.

Grain growth during protostellar disc formation

ABSTRACT Recent observations indicate that mm/cm-sized grains may exist in the embedded protostellar discs. How such large grains grow from the micron size (or less) in the earliest phase of star formation remains relatively unexplored. In this study, we take a first step to model the grain growth in the protostellar environment, using 2D (axisymmetric) radiation hydrodynamic and grain growth simulations. We show that the grain growth calculations can be greatly simplified by the ‘terminal velocity approximation’, where the dust drift velocity relative to the gas is proportional to its stopping time, which is proportional to the grain size. We find that the grain–grain collision from size-dependent terminal velocity alone is too slow to convert a significant fraction of the initially micron-sized grains into mm/cm sizes during the deeply embedded Class 0 phase. Substantial grain growth is achieved when the grain–grain collision speed is enhanced by a factor of 4. The dust growth above and below the disc midplane enables the grains to settle faster towards the midplane, which increases the local dust-to-gas ratio, which, in turn, speeds up further growth there. How this needed enhancement can be achieved is unclear, although turbulence is a strong possibility that deserves further exploration.

Hierarchical architecture and mechanical behavior of K418 Ni-based superalloys manufactured by laser powder bed fusion

Laser powder bed fusion (LPBF) has great potential in the manufacturing of difficult-to-cut Ni-based superalloys with complex geometries. The approach endows the alloys with multi-scale microstructure hierarchy, while its formation mechanism and contribution to mechanical properties are poorly understood. In this work, the hierarchical architecture in LPBF-fabricated K418 Ni-based superalloys, in terms of 3D interlocked grains, low-angle grain boundaries (LAGBs), cellular structure, inter-cellular segregation, and nano-sized γ′ precipitates and carbides, is comprehensively investigated. The formation of cellular structure is governed by the rapid solidification condition, and the 3D interlocked grain structure is associated with the cell growth behavior regulated by locally varied temperature gradient in the melt pool. The LPBF K418 alloys show a higher tensile strength but a slightly lower ductility at both room temperature and 600 °C than their conventional cast counterparts. The superior strength of LPBF alloys is dominantly attributed to the strengthening effect of interlocked grain boundaries and cellular microstructure. This work demonstrates the capability of LPBF to manufacture Ni-based superalloys with hierarchical microstructures and high performance for the application of hot-section gas turbine components.

Whether organic spacer cations induced 2D/3D or quasi-2D/3D mixed dimensional perovskites?

The dimensional engineering of perovskite films has been demonstrated to be an efficient technique to enhance both the efficiency and stability of perovskite solar cells (PSCs). Whether the alternative spacer cations induced 2D/3D or quasi-2D/3D mixed dimensional perovskites make a great difference in the photovoltaic performance and their stability of corresponding PSCs. But the research on this aspect is still insufficient, the crystal structure of the mixed dimensional perovskite is still unclear, which needs more in-depth research. This work adopted the alternative spacer cation of 4-(aminoethyl) pyridine (4-AEP) and the conventional phenylethylamine (PEA), to study their induced low-dimensional crystal phase in 3D perovskite and compare the effect on the performance of corresponding PSCs. We demonstrated that 4-AEP cation has induced 2D crystal phase (low n-value) at the 3D grain boundaries, while the PEA has induced quasi-2D (high n-value) one. As a result, the 4-AEP incorporated MAPbI3 (2D/3D) PSCs obtained a higher power conversion efficiency (PCE, 20.7%) than that of the PEA based quasi-2D/3D ones. More importantly, the 4-AEP based 2D/3D PSCs exhibited better moisture resistance and long-term stability when exposed to moisture and continuous light irradiation. Our work demonstrated that the alternative organic spacer cation could induce 2D or quasi-2D phase in 3D perovskite, but the 2D/3D mixed dimensional perovskite shows more favorable for obtaining highly efficient and stable perovskite solar cells.

Recent advances of lab-based diffraction contrast tomography – reconstruction speed benchmark testing and validations

Lab-based diffraction contrast tomography (DCT) enables the user to reconstruct 3D grain maps of polycrystalline materials non-destructively. For each grain, the morphology and crystallographic orientation, as well as derived properties such as grain boundaries, can be determined. Through two application examples this paper demonstrates the data acquisition and reconstruction speed of the current implementation and validates the resulting grain maps. Firstly, for a conventional Laue focusing scan of an AlCu sample comprising 340 grains, major performance enhancements of the reconstruction algorithm have reduced the reconstruction time from half a day to half an hour. The second example highlights an advanced scan with projection geometry of an oriented electrical steel sheet containing 7,800 grains. While the data collection time is around a day for each of the data sets, the boosted reconstruction of the advanced acquisition data takes half a day and gives the full grain map without the need for stitching. After the major algorithm speed enhancements, grain map qualities are comparable with misorientations below 0.02° and grain boundary distances less than a voxel for both samples.

3D grain mapping by laboratory X-ray diffraction contrast tomography implemented on a conventional tomography setup

Non-destructive 3D characterization of grain orientations, shapes and sizes, i.e. grain mapping, offers immense opportunities for studying microstructural evolution in polycrystalline materials. In addition to a number of well-established grain mapping techniques available at synchrotron facilities, a polychromatic variant - laboratory diffraction contrast tomography (LabDCT) - using lab-based x-rays, has been developed and commercialized. Yet, the product is bounded to a specific instrument and requires a commercial license, which limits the use on widely available laboratory instruments. To promote the availability of LabDCT, we have developed a grain reconstruction method and implemented it on a conventional X-ray tomography setup at the SIMaP laboratory for LabDCT grain mapping. First, we tested the grain reconstruction algorithm by comparing an input virtual grain structure and a reconstructed volume using the forward simulated diffraction projections from the input structure. Then, we experimentally characterized an AlCu alloy sample using LabDCT and validated the grain mapping result by a grain reconstruction from synchrotron DCT measurement. Last, perspectives on further development of generalizing LabDCT technique on conventional tomography setups are discussed.

Application of scalar auxiliary variable scheme to phase-field equations

It has been a continuing challenge to carry out simulations at time and spatial scales compatible with practical experimental observations. Here we implement a novel scalar auxiliary variable (SAV) scheme introduced in (Shen et al., 2018) for phase-field equations to drastically improve the numerical accuracy, efficiency and stability. We first bench-marked two representative phase-field method applications involving three-dimensional (3D) grain growth and spinodal phase separation. By implementing the SAV scheme within the state-of-the-art semi-implicit Fourier spectral scheme we achieved an order of magnitude improvement for the single-order-parameter Allen-Cahn equation and at least a 100% improvement for a set of multi-order-parameter Allen-Cahn equations for grain growth problems and the Cahn-Hilliard equation for compositional phase separation. More importantly, the efficiency enhancement of SAV becomes more dramatic as interfaces become sharper. Its application to the growth morphology and kinetics of β’-Mg7Nd precipitates demonstrates a remarkable improvement of more than 50 times in computational time. This work is expected to further stimulate the applications of phase-field simulations of a broad range of materials processes.

Grain Configuration of Solid Rocket Motor

The solid rocket motor upper stage for a space launch vehicle is a more efficient propulsion technology than the liquid rocket motor upper stage. Its grain design has the potential to be crucial in terms of lowering inert mass by adopting improved volume efficiency with the lowest practicable sliver size while keeping maximum strength. Specifically, the strategy for (3D) grain arrangement of the slot for the upper stage solid rocket engine has been described in this paper. The complex configuration is established by the design process, which takes place under a parametric model of geometry in (CAD) software and is typified by varied dynamics. When constructing solid propellant rocket motors, grain arrangement is a vital and critical step. Accurate estimates of grain geometric properties play a key role in performance prediction and can be a vital and critical stage in the design of solid propellant rocket motors. This research study proposes an effective performance-matching design framework for solid rocket motors that are tuned to suit a range of thrust performance criteria. The framework is constructed utilising an innovative and specialised general design technique that was designed to evaluate the general design parameters, which is given in this study. Because of the findings obtained, it can be stated that the recommended framework is a practical and efficient approach for solid rocket engine design and development.

Determining the Thickness Coating of Grinding Powders of Synthetic Diamond Based on a Specific-Surface Approach and using an Extrapolation-Affine 3D Model of Grain

: Methodological features of indirect determining of thickness coating of grains grinding powders of synthetic diamond are analyzed. A newly revised classification of known methods for determining the thickness of the coating is proposed. The prospects of the methods based on the application of an external specific surface are noted. A positive feature is the proposal to determine the thickness of the coating separately for each grain of the sample, followed by the generalization of the results by calculating the arithmetic mean. This calculation scheme allows you to get more reliable information about the thickness of the coating. The expediency of using an extrapolation-affine 3D grain model in such a calculation scheme is substantiated. Using the extrapolation-affininе 3D grain model allows for determining the thickness of the coating of diamond powder grains without the traditional assumption about the spherical shape of their grains and with less error. For an example of grinding powder AC125 400/315, the advantage of such a 3D model compared to a 3D model in the form of a sphere is proved. The method proposed on the basis of such methodical innovation can be used for powders of other abrasive materials.

The influence of grain shape and size on the relationship between porosity and permeability in sandstone: a digital approach

An accurate and reliable description of the porosity–permeability relationship in geological materials is valuable in understanding subsurface fluid movement. This is important for reservoir characterisation, energy exploitation, geological carbon storage (GCS) and groundwater contamination and remediation. Whilst the relationship between pore characteristics and porosity and permeability are well examined, further investigation into the influence of grain characteristics on porosity and permeability would be beneficial due to the inherent relationship between grains and pores. This work aims to determine whether incorporation of grain characteristics into a porosity–permeability model is effective in constraining this relationship. Two fully digital approaches to individual 3D grain analysis based upon watershed segmentation are compared to determine the most effective, yet simple, workflow applicable to core plugs of significantly compacted grains. The identification of an effective segmentation workflow will facilitate future work on similarly complex materials, removing the need for traditional time-consuming and manual techniques. We use the most effective approach of measuring grain shape (sphericity) and size (Feret diameter) alongside an established fully digital workflow to measure porosity and permeability to investigate the impact of grain characteristics on porosity and permeability. We show that grain sphericity and porosity exhibit a positive relationship whereas no such relationship exists with grain size. Measurements of grain sphericity are applied to calculate a Kozeny–Carman (K–C) type porosity–permeability fit which was found to be unsatisfactory, compared to a simpler fit excluding any grain parameters. This is possibly due to the lower sphericity of the studied grains, deviating significantly from the K–C assumption that grains are entirely spherical. The simpler fit is most suitable for the studied materials, showing that inclusion of grain characteristics is not effective for better defining the porosity–permeability relationship in a K–C paradigm for these samples. This highlights the need for a model capable of considering a range of grain sphericities to further constrain the porosity–permeability relationship.

Image-Based 3D Reconstruction of Granular Grains via Hybrid Algorithm and Level Set with Convolution Kernel

This study develops a novel method for reconstructing three dimensional (3D) granular grains from computed tomography (CT) images. Unlike previous studies requiring trial-and-error hyperparameters, the hybrid algorithm introduced here, integrating the random forest (RF) algorithm and enhanced by particle swarm optimization for automatic determination of hyperparameters, is the first to train the model for constituent classification and grain segmentation. In addition, and different from previous manual methods, a convolution kernel is applied to assign an initial level set function inside an individual grain and determine whether to activate the level function for automatically reconstructing 3D grains from a CT image. All results indicate the hybrid algorithm can rapidly search the optimum hyperparameters, providing a more effective way to identify the optimum RF-based model. This model segments grains with an accuracy of 90%, in comparison with a 52% accuracy achieved by the conventional watershed algorithm. The convolution kernel can accurately and automatically identify individual grains, avoiding manual assignment of an initial calculation area and ensuring grains are correctly reconstructed. Overall, the proposed method provides a more intelligent and effective way to reconstruct 3D grains from CT images.

Indirect Evaluation of the Thickness of Coatings on Synthetic-Diamond Powders with the Use of New 3D Grain Models

Indirect Evaluation of the Thickness of Coatings on Synthetic-Diamond Powders with the Use of New 3D Grain Models

Olivine Morphology and Fabric During Diffusion Creep: Pure Shear Experiments

AbstractWe deformed aggregates of Fe‐free olivine +20 vol% diopside in pure shear to study olivine grain morphology and fabric during diffusion creep. Samples were each deformed to a strain of around 0.7 at different temperatures and experimental durations, which resulted in different grain sizes among the samples due to grain growth. The sample microstructures were observed from each of the three principal stress directions, which revealed various 3D grain morphologies among the samples. Samples with tabular grains displayed a crystallographic preferred orientation (CPO) in olivine, while samples with weakly anisotropic grains had uniform CPOs. The CPO patterns vary from AG‐type (i.e., a uniaxial [010] concentration in the direction of sample shortening) to A‐type (i.e [010] and [100] concentrations in the directions of sample shortening and stretching, respectively), with intermediate types being the most common. The transition from AG‐ to A‐type fabrics is accompanied by a change from oblate to prolate grain morphologies. We explain the direct correlation between the olivine morphology and fabrics based on preferential grain‐boundary sliding (GBS) at boundaries with fewer steps (ledges). Oblate morphologies with well‐developed grain boundaries oriented parallel to (010) provide easy GBS along (010) and [h0l] planes and directions, respectively, while relatively prolate morphologies with boundaries parallel to (010) that are elongated along [100] provide easy GBS along (010) and [100] planes and directions, respectively. Boundaries form parallel to a particular crystallographic plane through differential grain growth in the directions of the crystallographic axes. Such grain growth causes fabric transitions during diffusion creep.

Effects of Insect Density, Movement Period, and Temperature on Three-Dimensional Movement and Distribution of Adult Cryptolestes ferrugineus (Coleoptera: Laemophloeidae).

Knowledge on three-dimensional (3D) movement and distribution of Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) in grain bulks assists in the prediction of their distribution inside a bin. The following experiments were conducted to determine the 3D dispersal patterns of adult C. ferrugineus in wheat with 14.5% moisture content: 1) at various insect densities (0.35, 1.77 and 3.53 A/kg (adults/kg) at 20°C and in 24 h movement period; 2) in different movement periods (6, 24, and 72 h) at 20°C and 0.35 A/kg insect density; and 3) at different temperatures (20, 30 and 35°C) at 0.35 A/kg density in 24 h movement period. To create the densities of 0.35, 1.77, and 3.53 A/kg, 100, 500, and 1,000 adults were introduced in about 285 kg wheat, respectively. The 285 kg of wheat was kept in 343 mesh cubes, which in turn were packed in a wooden box. The introduced adults were counted at the end of the movement periods. Adult C. ferrugineus tended to move downward from the point of introduction, and then diffused throughout the grain bulk. The effects of insect densities, movement periods, and temperatures on the dispersion pattern of insects were similar in 1D columns, 2D chambers, and 3D grain bulk.

Reconstructing dual-phase nanometer scale grains within a pearlitic steel tip in 3D through 4D-scanning precession electron diffraction tomography and automated crystal orientation mapping

The properties of polycrystalline materials are related to their microstructures and hence a complete description, including size, shape, and orientation of the grains, is necessary to understand the behavior of materials. Here, we use Scanning Precession Electron Diffraction (SPED) in the Transmission Electron Microscope (TEM) combined with a tilt series to reconstruct individual grains in 3D within a polycrystalline dual-phase cold wire-drawn pearlitic steel sample. Nanoscale ferrite grains and intragranular cementite particles were indexed using an Automated Crystallographic Orientation Mapping (ACOM) tool for each tilt dataset. The grain orientations were tracked through the tilt datasets and projections of the individual grains were reconstructed from the diffraction data using an orientation-specific Virtual Dark Field (VDF) approach for tomographic reconstruction. The algorithms used to process and reconstruct such datasets are presented. These algorithms represent an extension to the ACOM approach that may be straightforwardly applied to other multi-phase polycrystalline materials to enable 3D spatial and orientation reconstructions.

An Intelligent Analysis Method for 3D Wheat Grain and Ventral Sulcus Traits Based on Structured Light Imaging.

The wheat grain three-dimensional (3D) phenotypic characters are of great significance for final yield and variety breeding, and the ventral sulcus traits are the important factors to the wheat flour yield. The wheat grain trait measurements are necessary; however, the traditional measurement method is still manual, which is inefficient, subjective, and labor intensive; moreover, the ventral sulcus traits can only be obtained by destructive measurement. In this paper, an intelligent analysis method based on the structured light imaging has been proposed to extract the 3D wheat grain phenotypes and ventral sulcus traits. First, the 3D point cloud data of wheat grain were obtained by the structured light scanner, and then, the specified point cloud processing algorithms including single grain segmentation and ventral sulcus location have been designed; finally, 28 wheat grain 3D phenotypic characters and 4 ventral sulcus traits have been extracted. To evaluate the best experimental conditions, three-level orthogonal experiments, which include rotation angle, scanning angle, and stage color factors, were carried out on 125 grains of 5 wheat varieties, and the results demonstrated that optimum conditions of rotation angle, scanning angle, and stage color were 30°, 37°, black color individually. Additionally, the results also proved that the mean absolute percentage errors (MAPEs) of wheat grain length, width, thickness, and ventral sulcus depth were 1.83, 1.86, 2.19, and 4.81%. Moreover, the 500 wheat grains of five varieties were used to construct and validate the wheat grain weight model by 32 phenotypic traits, and the cross-validation results showed that the R2 of the models ranged from 0.77 to 0.83. Finally, the wheat grain phenotype extraction and grain weight prediction were integrated into the specialized software. Therefore, this method was demonstrated to be an efficient and effective way for wheat breeding research.