Defect-free Grain Research Articles

Effect of physical characteristics of coffee grain (Coffea arabica L.) cultivated in Temascaltepec, state of Mexico, on the roasting process

The Finca the Illusion produces coffee that earned second place in the 2018 and fourth place in the 2019 and 2021 “Cup of Excellence Mexico” competitions (represented by technician Federico Barrueta). Due to the scarce physicochemical and organoleptic information on coffee from the southern region of the State of Mexico, the objective of this study was to evaluate the physical and sensory characteristics of coffee (Coffea arabica L. var. Caturra Rojo) grown at Finca the Illusion in Temascaltepec, State of Mexico. A completely randomized design was established with two treatments (Finca the Illusion and Finca Soconusco) and three repetitions (350 g each). The variables analyzed in the coffee were defects, percentage of defect-free grain, density, moisture, water activity, and sensory evaluation of the beverage. At Finca the Illusion, the main defect was fungal damage, which can be prevented with proper practices during the collection of coffee cherry and classification of green coffee. The moisture (10.1%), density (0.69 kg/L), and water activity value (0.51) were within the optimal range. The roasting was medium-light, and the cupping score was 86, corresponding to an Excellent Specialty Origin coffee.

Effect of tool pin shapes on microstructure and mechanical behaviour of friction stir welding of dissimilar aluminium alloys

The mechanical and microstructure characterizations of friction stir welding (FSW) joints of 5052-H32 with 6061-T6 aluminium alloys (AA) were investigated in this research. With two distinct tools (Taper cylinder and Threaded cylinder), the microstructural change associated to the mechanical characteristics of an FSW of dissimilar AA has been investigated under constant welding conditions such as welding speed (WS) and tool rotation speed (TRS) are 60 mm/min and 900 rpm respectively. For instance, in the hardness profile, the lesser values were obtained in the AA6061 alloy. The maximum and minimum weld joint strength were approximately 165.84 MPa and 133.85 MPa from the FSW, showed lower strength than the base material. The highest joint Efficiency of the dissimilar weld was 78.37 %, and the maximum hardness is 71 HV obtained. The defect-free stir zone development and grain size strengthening were credited with it as well. The elongations of the welded joints were measured to be 11.6 % and 7.2 %. It was discovered that using a tool with a taper pin profile and a threaded pin profile produced a joint with better tensile strength, a larger nugget area, and a smoother surface finish. Finally, it was discovered that a fine grain microstructure created by using a taper pin profile resulted in stronger welded connections compared with threaded pin profile.

Influence of powder characteristics on cold sintering of nano-sized ZnO with density above 99 %

Cold sintering parameters such as, temperature, pressure, aqueous phase, heating rate and dwelling time has been widely discussed in the literature but the role of starting powder with respective microstructure development is mostly overlooked. There is a need for understanding the effect of powder agglomerates and the role of inter particle friction on the densification behavior during cold sintering process. Present study encompasses investigation and optimization of these parameters for ZnO which enabled > 99 % of relative density with grain sizes below 200 nm. Additionally, role of external atmosphere was also studied to investigate its impact on densification during the process. All cold sintering experiments were carried out in a FAST/SPS device for studying aqueous phase evaporation and ensuring the reproducibility of process parameters. Microstructure characterization (scanning and transmission electron microscopy) showed – without any post heat treatment– defect free grain boundary structure opposite to what documented by previous studies.

Periodic formations of deformation twins and dislocation arrays via grain boundary sliding at serrated grain boundary in cold-shear-strained AZ31 alloy

It is well known that grain boundary sliding (GBS) provides stress concentration and initiates grain boundary fracture at the serrated grain boundary or grain triple junction during high-temperature creep. Recent reports on GBS occurring during deformation at room temperature suggest that stress concentration may occur due to GBS, which has a stress component parallel to the grain boundary plane, even in cold working. To identify if GBS can generate stress concentration and related defects at the grain boundary at room temperature, we experimentally investigated periodic defect formation along the serrated grain boundary during cold shear deformation. To obtain defect-free serrated grain boundary structure, optimal conditions of hot-torsion and annealing were determined. Cylindrical torsion specimens were then machined into notched tensile specimens, which provide the advantage of directly observing the GBS and lattice curvature. Extensive observations and orientation analysis on periodic defect formation along the serrated grain boundary suggest that GBS at room temperature can periodically nucleate twinning as well as dislocation arrays. Crystal plasticity simulation proved that serrated GB generates non-rotating region and split stress distribution with intensified value. Two stress concentration mechanisms during the accommodation of GBS at the serrated grain boundary were proposed: direct transfer from rotational stress and indirectly formed tensile component, namely “cleavage stress.” While direct energy transfer was likely to follow the local Schmid's law for direction of the grain rotation, cleavage accommodation represented geometrically necessary characteristics.

Microstructure characterization and corrosion resistance properties of Pb-Sb alloys for lead acid battery spine produced by different casting methods.

The aim of this study is to find out the microstructure, hardness, and corrosion resistance of Pb-5%Sb spine alloy. The alloy has been produced by high pressure die casting (HPDC), medium pressure die casting (AS) and low pressure die casting (GS) methods, respectively. The microstructure was characterized by using optical microscopy and scanning electron microscopy (SEM). The hardness was also reported. The corrosion resistance of the spines in 0.5M H2SO4 solution has been analyzed by measuring the weight loss, impedance spectroscopy and the potentiodynamic polarization techniques. It has been found that the spine produced by HPDC has defect-free fine grain structure resulting improvement in hardness and excellent corrosion resistance.

Elemental redistributions at structural defects in Cu(In,Ga)Se2 thin films for solar cells

The microstructural evolution of Cu(In,Ga)Se2 absorber layers during a three-stage-type co-evaporation process was studied to elucidate the effect of a Cu-rich stage on the formation of extended structural defects. Defect densities for two Cu-poor samples, one interrupted before and one after this crucial Cu-rich composition stage, were investigated by scanning transmission electron microscopy (STEM) imaging. The structure and chemical nature of individual defects were investigated by aberration-corrected high-resolution STEM in combination with electron energy-loss spectroscopy on the atomic-scale. In spite of the different defect densities between the two samples, most of the individual defects exhibited similar chemistry. In particular, the elemental distributions of atomic columns at {112} twin planes, which are very frequent in Cu(In,Ga)Se2 thin films, were found to be the same as in the defect-free grain interiors. In contrast, within grain boundaries, dislocation cores, and other structurally more complex defects, elemental redistributions of Cu and In were observed.

Nanoscale Block Copolymer Ordering Induced by Visible Interferometric Micropatterning: A Route towards Large Scale Block Copolymer 2D Crystals

We have overcome the cost and time consumption limitations of common lithography techniques used to control the self-assembly of block copolymers into highly ordered 2D arrays through the use of a guiding pattern created from a polymeric sub-layer. The guiding pattern is a sinusoidal surface-relief grating interferometrically inscribed onto an azobenzene containing copolymer sub-layer leading to a defect-free single grain of block copolymer domains.

Mean Shift-Based Defect Detection in Multicrystalline Solar Wafer Surfaces

This paper presents an automated visual inspection scheme for multicrystalline solar wafers using the mean-shift technique. The surface quality of a solar wafer critically determines the conversion efficiency of the solar cell. A multicrystalline solar wafer contains random grain structures and results in a heterogeneous texture in the sensed image, which makes the defect detection task extremely difficult. Mean-shift technique that moves each data point to the mode of the data based on a kernel density estimator is applied for detecting subtle defects in a complicated background. Since the grain edges enclosed in a small spatial window in the solar wafer show more consistent edge directions and a defect region presents a high variation of edge directions, the entropy of gradient directions in a small neighborhood window is initially calculated to convert the gray-level image into an entropy image. The mean-shift smoothing procedure is then performed on the entropy image to remove noise and defect-free grain edges. The preserved edge points in the filtered image can then be easily identified as defective ones by a simple adaptive threshold. Experimental results have shown the proposed method performs effectively for detecting fingerprint and contamination defects in solar wafer surfaces.

Formation of a high-coercive state in sintered Nd-Fe-B-Ga magnets by thermocycling

A comparative investigation of the effect of two types of low-temperature annealing, namely, (1) isothermal treatment and (2) thermocycling treatment (TCT), on the coercive force H c of sintered magnets of an Nd-Fe-B-Ga alloy has been performed. Powders of an Nd 15.5 Fe 77.7 B 6.5 Ga 0.3 alloy were prepared from materials taken in three different conditions: cast alloy (CA), hydrided alloy (HA), and partly dehydrided alloy (PDA). The coercive force of the sintered magnets reaches different maximum values, depending on the time of grinding, which after isothermal annealing at 550°C are 680, 688, and 800 kA/m in the magnets prepared from the CA, HA, and PDA, respectively. It has been revealed that the subsequent application of a TCT con- sisting in the variation of the temperature in a range of 20-550°C additionally increases H c . In fine-grained magnets the increment in H c is 10-15%; in coarse-grained, 100-300%. Thus, after a TCT the extremal depen- dence of H c on the time of grinding of the powder virtually vanishes. To explain the observed effect of a TCT, an assumption is made on the effect of interphase stresses (arising at the boundaries between the grains and the intergrain phase enriched in Nd) on the mobility of atoms and the formation of defect-free grain boundaries, which favor an increase in H c upon annealing.

Quantitative in situ nanoindentation in an electron microscope

We report the development of a method for quantitative, in situ nanoindentation in an electron microscope and its application to study the onset of deformation during the nanoindentation of aluminum films. The force–displacement curve developed shows the characteristic “staircase” instability at the onset of plastic deformation. This instability corresponds to the first appearance of dislocations in a previously defect-free grain. Plastic deformation proceeds through the formation and propagation of prismatic loops punched into the material, and half loops that emanate from the sample surface. These results represent the first real time observations of the discrete microstructural events that occur during nanoindentation.

Excimer Laser Annealing Effect on MILC Polycrystalline Silicon Film

AbstractXeCl excimer laser was irradiated on metal induced laterally crystallized (MILC) polycrystalline silicon (poly-Si) film in order to eliminate the intra-grain defects of MILC poly-Si film which incorporated 2 μm wide metal induced crystallized (MIC) poly-Si line pattern. On the irradiation of the laser beams, different melt and recrystallization phenomena were observed in the MILC and the MIC poly-Si region due to the Ni content difference in each film. The transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS) measurements indicated that the melting temperature of the poly-Si film decreased as the Ni content increased. With the laser irradiation energy density of 370 mJ/cm2, 2 μm long defect-free poly-Si grain was successfully grown in the MILC poly-Si due to the melting temperature variation at the MILC-MIC poly-Si boundary.

On the Toroidal Arrangement of the 180° Domain Walls in Ring Polycrystalline Soft Ferrites

According to an assumption proposed by Globus in 1976, special ring-shaped polycrystalline soft ferrites could have a toroidal arrangement of their magnetic domains (so-called magnetic ring concept). Experiments in the past have shown that this property must be restricted to the defect-free grain microstructures. This paper gives two examples of investigations wich confirm the good validity of the concept. The first example is concerned with the magnetoelastic effects of the mechanical compression applied along the circumferences of the ring sample. λ being negative (YIG), the spins are forced to align in the stress direction leading to a more or less marked increase of the initial susceptibility (measurement is made in the same direction as the stress applied) according to the aptitude of the sample investigated to obey the above concept. In the most favourable cases, the axial direction (the revolution axis of the ring), can be then approached as a true hard magnetization axis, so that it becomes possible to interpret the magnetization in this direction as an irreversible rotational process. The second investigation is thus the analysis of the magnetization in this so-called hard direction. Comparisons with a theoretical development of the hysteresis of rotation are made which lead to good agreements.

A quantitative description of recrystallization and grain growth in single phase b.c.c. iron

This paper provides a description of the geometrical aspects of static recrystallization in α-Fe. Geometrical properties of two-dimensional sections, volume, shape and spatial distribution of nuclei/grains have been measured and from them, using stereological methods, three-dimensional microstructural evolution has been followed. The results show that recrystallization nuclei in α-Fe form clusters and that the nucleation of defect-free nuclei and grain growth occurs concurrently during recrystallization. The recrystallization process is characterized not only by changes in the size of nuclei/grains but also by alterations in their shape.

Trapping of hydrogen and helium at grain boundaries in nickel: An atomistic study

Atomistic computer simulations of the trapping of hydrogen and helium at defect free grain boundaries in nickel are presented. Three symmetrical tilt boundaries that encompass a number of compact polyhedra of atoms are considered as regions of potential trapping sites. By employing the structural unit model, these boundaries are shown to be representative of a wide range of grain boundary structures. A general correspondence of trap locations in regions of expansion for both hydrogen and helium has been found; however, the binding energy for helium trapping is much greater than that for hydrogen. Consequently, clean grain boundaries in nickel appear to be important trapping sites for helium, but not significant sites for hydrogen binding. These results are consistent with experimental autoradiography, thermal desorption, and transmission electron microscopy observations. They imply that grain boundary trapping plays an important role in mechanisms of helium embrittlement, but not in hydrogen embrittlement of nickel.

A microstructural investigation of the bcc to A15 phase transition in sputter-deposited Nb3Al superconductors

The bcc to A15 phase transition in sputter-deposited Nb3Al (Cb3Al) superconductors was studied using transmission electron microscopy. Four distinct microstructures were observed for the sputter-deposited and isochronally heat treated samples. Heat treatments were for 24 h at temperatures between 500 and 700°C. Deposition at 10°C produced the bcc phase with a small grain size of 1000A. The bcc grains contained a high density of dislocations and fine precipitates. Coarse precipitates were found in the bcc grains and at the grain boundaries after heat treatment between 500 and 600°C. At 650°C, the A15 phase was detected in the presence of the bcc phase; the nucleation of the A15 phase originated at the grain boundary. Finally, a homogeneous microstructure of A15 phase resulted from heat treatment at 700°C. The A15 phase had a small, but defect free grain of 2500A. It is believed that such microstructures of A15 phase could have enhanced superconducting critical current (Jc) and critical temperature (Tc).

Forces necessary to displace a defect-free grain boundary

A systematic study was undertaken to calculate the energy associated with displacing a defect-free grain boundary from its minimum energy configuration. The energy required to slide the two crystals with respect to each other was determined by using pairwise potentials to simulate the atomic interactions. The energy required to displace the crystals was used to determine the forces necessary to displace the two crystals in the grain boundary plane. This study showed that the contours of the energy versus displacement curves were similar in the vicinity of the minimum for displacements in the boundary plane, both parallel and perpendicular to the tilt axis. Furthermore, the energy profiles were similar for both the case where the separation of the two crystals perpendicular to the boundary plane was adjusted to obtain the minimum energy, and the case where the separation was held constantSeveral potentials were employed in this study, and the energy contours appeared to be relatively independent of the potential used. However, it was found that those potentials adjusted for truncation of the neighbour separation produced smoother curves and the resulting forces showed less perturbation in the vicinity of the minimum. The conclusion of this study is that for substantial grain boundary displacements to occur in real materials some sort of grain boundary defect would be required, since the forces required to displace defect-free boundaries are higher than observed. Résumé Une étude systematique a été entreprise afin de calculer l' énergie requise pour Ie déplacement, à partir de sa configuration d' énergie minimale, d'un joint de grain libre de défaut.L' énergie requise pour faire glisser les deux cristaux l'un par rapport agrave; l'autre a été déterminée en utilisant des potentiels en couple dans Ie but de simuler les interactions atomiques. L' énergie requise pour Ie déplacement des cristaux a été utilisée pour déterminer les forces nécessaires à ce déplacement dans Ie plan du joint. Cette étude a révélé que les contours d'énergie en fonction des courbes de déplacement sont semblables au voisinage du minimum dans Ie cas de déplacements dans Ie plan du joint, et ce, pour des duections paralléles ou perpendiculaires à l'axe de flexion. De plus, les profils d'énergie sont semblables dans Ie cas pour lequel la séparation entre les deux cristaux, perpendiculaire au plan du joint, était ajustée pour obtenir l' énergie minimale, et également dans les cas pour lesquels la séparation était maintenue con stante.Plusieurs potentiels furent utilisés dans cette étude et les contours d' énergie se sont révélés ètre relativement indépendants du potential employé. Cependant, il est apparu que les potentiels ajustés pour obtenir une diminution de la distance entre plus proches voisins donnaient des courbes plus lisses et les forces résultantes présentaient moins de variation au voisinage du minimum. La conclusion de cette étude est que tout déplacement important des joints de grains, dans des métaux réels, doivent impliquer certains types de défauts, car les forces requises pour déplacer des joints libres de défaut sont plus élevées que celles observées expérimentalement.

Forces necessary to displace a defect-free grain boundary

A systematic study was undertaken to calculate the energy associated with displacing a defect-free grain boundary from its minimum energy configuration. The energy required to slide the two crystals with respect to each other was determined by using pairwise potentials to simulate the atomic interactions. The energy required to displace the crystals was used to determine the forces necessary to displace the two crystals in the grain boundary plane. This study showed that the contours of the energy versus displacement curves were similar in the vicinity of the minimum for displacements in the boundary plane, both parallel and perpendicular to the tilt axis. Furthermore, the energy profiles were similar for both the case where the separation of the two crystals perpendicular to the boundary plane was adjusted to obtain the minimum energy, and the case where the separation was held constantSeveral potentials were employed in this study, and the energy contours appeared to be relatively independent of the potential used. However, it was found that those potentials adjusted for truncation of the neighbour separation produced smoother curves and the resulting forces showed less perturbation in the vicinity of the minimum. The conclusion of this study is that for substantial grain boundary displacements to occur in real materials some sort of grain boundary defect would be required, since the forces required to displace defect-free boundaries are higher than observed. Résumé Une étude systematique a été entreprise afin de calculer l' énergie requise pour Ie déplacement, à partir de sa configuration d' énergie minimale, d'un joint de grain libre de défaut.L' énergie requise pour faire glisser les deux cristaux l'un par rapport agrave; l'autre a été déterminée en utilisant des potentiels en couple dans Ie but de simuler les interactions atomiques. L' énergie requise pour Ie déplacement des cristaux a été utilisée pour déterminer les forces nécessaires à ce déplacement dans Ie plan du joint. Cette étude a révélé que les contours d'énergie en fonction des courbes de déplacement sont semblables au voisinage du minimum dans Ie cas de déplacements dans Ie plan du joint, et ce, pour des duections paralléles ou perpendiculaires à l'axe de flexion. De plus, les profils d'énergie sont semblables dans Ie cas pour lequel la séparation entre les deux cristaux, perpendiculaire au plan du joint, était ajustée pour obtenir l' énergie minimale, et également dans les cas pour lesquels la séparation était maintenue con stante.Plusieurs potentiels furent utilisés dans cette étude et les contours d' énergie se sont révélés ètre relativement indépendants du potential employé. Cependant, il est apparu que les potentiels ajustés pour obtenir une diminution de la distance entre plus proches voisins donnaient des courbes plus lisses et les forces résultantes présentaient moins de variation au voisinage du minimum. La conclusion de cette étude est que tout déplacement important des joints de grains, dans des métaux réels, doivent impliquer certains types de défauts, car les forces requises pour déplacer des joints libres de défaut sont plus élevées que celles observées expérimentalement.