Axes Of Grains Research Articles

Unique deformation mechanisms of extruded Mg–Y-Sm-Zn-Zr alloy

In present work, the effect of C texture, with the c axis of grains aligned parallel to extrusion direction (ED), on the deformation modes during tension in extruded Mg–Y-Sm-Zn-Zr alloy was investigated. The results indicated that both the extension twins and pyramidal <c+a> dislocations were activated, whereas basal <a> and prismatic <a> dislocations remained dormant during the early stages of tension. With the increase in tensile strain, the number fraction of extension twins increased continuously and rotated their orientation towards the direction perpendicular to ED. Meanwhile, the prismatic slip was activated in the newly orientated grains exhibiting a deviation angle >60°with respect to ED based on the intragranular misorientation axis (IGMA) analysis. Additionally, Viscoplastic self-consistent (VPSC) simulation confirmed that the activation of pyramidal <c+a>, prismatic <a>, extension twin, coupling with the suppression of basal <a> slip attributed to the highest critical resolved shear stress (CRSS) of basal <a> dislocation. Further analysis by TEM revealed that the precipitation of LPSO and γ′ on the basal plane of Mg, along with the increased volume fraction of extension twin actively obstructed the movement of <a> dislocations, consequently elevating the critical resolved shear stress (CRSS) in basal <a> slip.

Simulation of the movement of rice grains in a centrifugal huller by discrete element method and the influence of blade shape

Problems of low one-time hulling ratio and high grain breakage can occur during rice processing. Understanding the interaction mechanism between grains and blade in a centrifugal huller is the key to improving its performance. In this study, the discrete element method was used to simulate the movement of rice in centrifugal huller. The feasibility of simulation and particle modelling was confirmed by experiments. The results showed that some grains can lack the necessary acceleration, which can lead to the velocity difference between grains. With increasing radial position, the orientation angle of grains gradually changed to angles that were not conducive to hulling. The friction work done by the blade to the grains causes reductions in the rotational kinetic energy of the grains. When the grains are located alongside the upper or the lower layers of the huller wall, the proportion of grains moving at their optimal hulling angle is greater and the long axis of grain tends to be adjusted to become parallel to the baffle. Based on the principle of minimising the rebound of grains on the blades and reducing the rotational kinetic energy of grains themselves, a new type of V-shaped concave blade was investigated. Compared with original blade, the hulling ratio was increased by 8% and breakage ratio was decreased by 7.33% using the concave blade. This study can provide theoretical guidance for the design of centrifugal huller or similar grain processing equipment.

Comparison of three grain size measuring methods applied to coarse-grained gravel deposits

The size of grains in gravel and conglomerate deposits is most easily measured on photos taken from related outcrops. However, the occlusion of grains by the sedimentary matrix or other grains, and possible distortions of photos, could introduce a bias in such datasets. Here, we explore the uncertainties associated with datasets where the lengths of the grains were measured on photos. To this end, we analysed coarse-grained (>2 mm) fluvial material from a gravel pit (Bern, Switzerland). We compared grain size data collected from digital photos with the results where the same material was measured with a calliper and mechanically sieved. Our analyses reveal that the percentile values such as the D16, D50 and D84 of datasets where the grains' longest visible axes were measured on digital photos best correlate to the corresponding percentile values of data collected through sieving. We also find that the longest visible axes of grains measured on digital photos are c. 17 % smaller than the lengths of the intermediate b-axes of grains measured with a calliper. We therefore suggest to measure the longest visible axes on digital photos, and to correct the data by a corresponding factor such as +17 % for the target grain size percentiles.

Giant Magnetoresistance and Magnetocaloric Effect in Highly Textured Ni45Mn36.5In13.5Co5 Alloys

Herein, the giant magnetoresistance (MR) and magnetocaloric effect (MCE) of highly textured Ni45Mn36.5In13.5Co5 alloys are investigated. The Ni45Mn36.5In13.5Co5 alloys are grown using the liquid‐metal‐cooling directional solidification technique. In the scanning electron microscopy (SEM) image, unique bamboo‐like transverse stripes perpendicular to the long axis of grains are observed, which may lead to the giant MR of the sample. For the magnetic field change of 10 kOe, the giant MR value at 268 K is ≈−64%, which is rather big among similar bulk alloys. The MCE is evaluated via the magnetic entropy change. In H⊥ and H∥ magnetic fields of 30 kOe, the maximum entropy change is 13.5 and 15.3 J kg−1 K−1, and the effective refrigeration capacity (RC) reaches ≈108 and ≈117 J kg−1. The detailed results indicate that the MCE properties of the studied alloys vary in different directions under a low magnetic field; however, the difference is not very significant under a high magnetic field.

Insights into grain boundary energy structure-property relationships by examining computed [1 0 0] disorientation axis grain boundaries in Nickel

A study of 346 computed [1 0 0] disorientation axis grain boundaries provides insight into grain boundary energy structure-property relationships. The grain boundaries come from 6 coincidence site lattice misorientations at regularly spaced disorientation angles, and cover the full range of boundary plane orientations. The computed energy has clear trends in disorientation angle and boundary plane orientation. The data are used to reexamine the ‘special’ attribute frequently applied to low Σ coincidence site lattice misorientations and low-angle boundaries and to assess the accuracy of a face-centered cubic grain boundary energy function developed by Bulatov, Reed, and Kumar (Acta Mater. 65 (2014) 161-175).

Impurity Effect of Light Elements on the Nickel Crystallization in the Triple Junction Region of Grain Boundaries: Molecular Dynamics Simulation

The impurity effect of light elements (carbon, nitrogen, and oxygen) on nickel crystallization in the triple junction region of grain boundaries is studied by the molecular dynamics method. The tilt grain boundaries with disorientation axis 〈111〉 are considered as grain boundaries. The computational cell is a cylinder, the axis of which coincided with the triple junction and the disorientation axis of grains. Periodic boundary conditions are imposed along the cylinder axis; the atoms on the lateral surface of the cylinder are stationary. To simulate crystallization, the computational cell was melted by heating to a temperature significantly higher than the melting point of nickel. After the simulated polycrystal became liquid, the thermostat was turned on and the polycrystal was kept at a constant temperature less than melting point. In this case, the rigid boundary conditions on the lateral surface of a cylindrical computational cell simulated the crystallization fronts from three crystallization centers. The area near the triple junction crystallized in the last turn. Defects and free volume are concentrated in this area. The impurities significantly slowed down the crystallization rate. The addition of 10% impurity atoms slowed down the rate of the crystallization front by several times. The impurity effect on the crystallization rate increased in the direction C–N–O. This is due to the difference in the deformation of the crystal lattice caused by impurity atoms: the greater this deformation, the more impurity atoms slow down the crystallization front. Impurity carbon atoms formed aggregates of crystal grains at rather high concentrations. Crystallization front remained on these aggregates. Oxygen atoms and nitrogen atoms did not form aggregates; nevertheless, they distorted the crystal lattice and significantly slowed down the crystallization front.

Surface Diffusion Constants and Supersaturations in SmBCO Films Prepared by Pulsed Laser Deposition Method

REBa 2 Cu 3 Oy (REBCO, RE = rare earth) coated conductors are required for high current carrying capability. Self-organization of Ba-M-O (BMO, M = Zr, Sn, Hf...) is available to improve critical current density (J c ) in magnetic field, and suppression of a-axis grain growth contributes to enhance J c . The former and latter are affected by the surface diffusion of adatoms and supersaturation in the REBCO film growth, respectively. We focused on surface morphologies of SmBa 2 Cu 3 O y (SmBCO) films deposited by the pulsed laser deposition method in this paper, and estimated surface diffusion constant and supersaturation from the surface morphologies. As a result, an activation energy of the surface diffusion was approximately 2.2 eV and the value is somewhat smaller than 2.5 eV for YBCO films. Additionally, we found that a-axis grains appeared when supersaturation (Δμ) became higher than a threshold Δμ . Interestingly, a seed layer consisting of c-axis oriented SmBCO suppressed a -axis grain growth. These findings are useful to improve J c in REBCO coated conductors.

Effect of deformation ratios on grain alignment and magnetic properties of hot pressing/hot deformation Nd-Fe-B magnets

The magnetic properties, microstructure and orientation degrees of hot pressing magnet and hot deformation Nd-Fe-B magnets with different deformation ratios have been investigated in this paper. The remanence (Br) and maximum magnetic energy product ((BH)max) were enhanced gradually with the deformation ratio increasing from 0% to 70%, whereas the coercivity (HCj) decreased. The scanning electron microscopy (SEM) images of fractured surfaces parallel to the pressure direction during hot deformation show that the grains tend to extend perpendicularly to the c-axes of Nd2Fe14B grains under the pressure, and the aspect ratios of the grains increase with the increase of deformation ratio. Besides, the compression stress induces the long axis of grains to rotate and the angle (θ) between c-axis and pressure direction decreases. The X-ray diffraction (XRD) patterns reveal that orientation degree improves with the increase of deformation ratio, agreeing well with the SEM results. The hot deformation magnet with a deformation ratio of 70% has the best Br and (BH)max, and the magnetic properties are as followed: Br=1.40 T, HCj=10.73 kOe, (BH)max=42.30 MGOe.

Novel mechanisms for solid-state processing and grain growth with microstructure alignment in alnico-8 based permanent magnets

An estimated 750,000 new hybrid electric and plug-in battery vehicles, most with permanent magnet synchronous alternating current (PMAC) drive motors, took to the road in 2016 alone. Accompanied by 40% year over year growth in the EV market significant challenges exist in producing large quantities of permanent magnets (on the order of tens of millions) for reliable, low-cost traction motors [IE Agency, Energy Technology Perspectives (2017)]. Since the rare earth permanent magnet (REPM) market is essentially 100% net import reliant in the United States and has proven to have an unstable cost and supply structure in recent years, a replacement RE-free PM material must be designed or selected, fully developed, and implemented. Alnico, with its high saturation magnetization and excellent thermal stability, appears to be uniquely suited for this task. Further, while alnico typically has been considered a relatively low coercivity hard magnet, strides have been made to increase the coercivity to levels suitable for traction drive motors [W Tang, IEEE Trans. Magn., 51 (2015)]. If a simple non-cast approach for achieving near [001] easy axis grain aligned permanent magnets can be found, this would allow mass-produced final-shape anisotropic high energy product magnets suitable for usage in compact high RPM rotor designs. Therefore, a powder metallurgical approach is being explored that uses classic compression molding with “de-bind and sinter” methods, where a novel applied uniaxial loading, and an applied magnetic field may create final-shape magnets with highly textured resulting microstructures by two different mechanisms. Results indicate a positive correlation between applied uniaxial load and resulting texture (Fig. 1), along with benefits from using an applied magnetic field for improved texture, as well. The apparent mechanisms and resulting properties will be described using closed loop hysteresisgraph measurements, EBSD orientation mapping, and high-resolution SEM.

Magnetic fabric (anisotropy of magnetic susceptibility) constraints on emplacement mechanism of clastic dikes

AbstractClastic dikes are generally classified into neptunian and injected dikes. Using the magnetic fabrics (AMS: anisotropy of magnetic susceptibility), we attempt to classify the clastic dikes in the Late Cretaceous Dadaepo Basin, SE Korea, and interpret their emplacement mechanisms. The neptunian dikes exhibit a typical oblate sedimentary fabric which makes a sharp contrast with the injected dikes. The fabrics of the injected dikes are greatly influenced by current conditions and transportation types of filling materials. Based on the AMS fabrics, they are classified into four types. (1) VP (vertical flow‐parallel) type is formed by imbrication of long axis of grains in low‐ to moderate‐energy vertical flow of a Newtonian fluid and characterized by a bilateral symmetry of fabrics across the dike. (2) VT (vertical flow‐transverse fabric) type results from grain rolling in vertical high‐energy flow and is characterized by subvertical k2 and subhorizontal k1 axes on the dike plane. (3) HP (horizontal flow‐parallel) type is formed by imbrication of long axis of grains in horizontal low‐ to moderate‐energy flow, resulting in subvertical k3 and subhorizontal k1 and k2 axes. (4) HT (horizontal flow‐transverse) type is formed by grain rolling in horizontal high‐energy flow, resulting in streaked k2‐k3 on the dike plane and horizontally clustered k1 axes. The AMS fabrics of each type can be a significant indicator for flow direction. Based on abundant AMS fabrics formed by high‐energy current, coexistence of paleoseismic structures, and tectonic setting of the basin, earthquake‐induced liquefaction is the most plausible trigger for the dike formation.

Pore scale evaluation of thermal conduction anisotropy in granular porous media using Lattice Boltzmann method

PurposeThermal conduction anisotropy, which is defined by the dependency of thermal conductivity on direction, is an important parameter in many engineering and research studies such as the design of nuclear waste depositional sites. In this context, the authors aim to investigate the effect of grain shape in thermal conduction anisotropy using pore scale modeling that utilizes real shapes of grains, pores and throats to characterize petrophysical properties of a porous medium.Design/methodology/approachThe authors generalize the swelling circle approach to generate porous media composed of randomly arranged but regularly oriented elliptical grains at various grain ratios and porosities. Unlike previous studies that use fitting parameters to capture the effect of grain–grain thermal contact resistance, the authors apply roughness to grains’ surface. The authors utilize Lattice Boltzmann method to solve steady state heat conduction through medium.FindingsBased on the results, when the temperature field is not parallel to either major or minor axes of grains, the overall heat flux vector makes a “deviation angle” with the temperature field. Deviation angle increases by augmenting the ratio of thermal conductivities of solid to fluid and the aspect ratios of grains. In addition, the authors show that porosity and surface roughness can considerably change the anisotropic properties of a porous medium whose grains are elliptical in shape.Originality/valueThe authors developed an algorithm for generation of non-circular-based porous medium with a novel approach to include grain surface roughness. In previous studies, the effect of grain contacts has been simulated using fitting parameters, whereas in this work, the authors impose the roughness based on the its fractal geometry.

Intrinsic flux pinning mechanisms in different thickness MgB2 films

MgB2 films in four thickness (60 nm, 200nm, 600nm and 1μm) have been fabricated by hybrid physical–chemical vapor deposition technique (HPCVD). By measuring the magnetization hysteresis loops and the resistivity, we have obtained the transport and magnetic properties of the four films. After that, the pinning mechanisms in them were discussed. Comparing the pinning behaviors in these ultrathin films, thin films and thick films, it was found that there exist different pinning types in MgB2 films of different thickness. In combination with the study of the surface morphology, cross-section and XRD results, we concluded that MgB2 films had different growth modes in different growth stages. For thin films, films grew along c axis, and grain boundaries acted as surface pinning. While for thick films, films grew along c axis at first, and then changed to a-b axis growth. As a result, the a-b axis grains acted as strong volume pinning.

All-in-one operation for dense-seeding of soybean with narrow-row, combining a vertical axis rotary harrow and grain drill

All-in-one operation for dense-seeding of soybean with narrow-row, combining a vertical axis rotary harrow and grain drill

Shear-Coupled Grain Growth and Texture Development in a Nanocrystalline Ni-Fe Alloy during Cold Rolling

The evolution of texture, grain size, grain shape, dislocation, and twin density has been determined by synchrotron X-ray diffraction and line profile analysis in a nanocrystalline Ni-Fe alloy after cold rolling along different directions related to the initial fiber and the long axis of grains. The texture evolution has been simulated by the Taylor-type relaxed-constraints viscoplastic polycrystal model. The simulations were based on the activity of partial dislocations in correlation with the experimental results of dislocation density determination. The concept of stress-induced shear coupling is supported and strengthened by both the texture simulations and the experimentally determined evolution of the microstructure parameters. Grain growth and texture evolution are shown to proceed by the shear coupling mechanism supported by dislocation activity as long as the grain size is not smaller than about 20 nm.

Structural, ferroelectric and magnetic properties of BiFeO3 synthesized by sonochemically assisted hydrothermal and hydro-evaporation chemical methods

BiFeO3 powders were synthesized by sonochemically assisted hydrothermal and hydro-evaporation methods. The X-ray diffraction confirmed the presence of secondary phases, Bi25FeO39 and Bi2Fe4O9, in as prepared BiFeO3 powders. Optimization of sintering conditions indicated that temperature of 800°C and time of 2h after pressing at 9t/cm2 provided ceramics samples with the highest density (up to 96% of theoretical density) and the lowest content of secondary phases. Ferroelectric and magnetic characterization was performed on two selected ceramics samples with the highest densities. Ceramics obtained from the powder synthesized by the hydrothermal method showed greater lattice distortion along [111] axis and smaller grains, which resulted in larger values of electric polarization at room temperature. It also exhibited less Fe(3d)–O(2p) orbital overlapping due to a larger FeOFe bond angle, causing lower antiferromagnetic ordering and weak ferromagnetic behavior at low temperatures.

Anisotropy of Mechanical Properties and its Correlation with the Structure of the Stainless Steel 316L Produced by the SLM Method

Standard specimens made of austenitic stainless steel powder 316L were produced by the SLM method. Studies of the mechanical properties showed a strong dependence on the parameters of powder melting and the direction of specimens building. It is stated that the yield strength and tensile strength are higher than that of a stainless steel specimens obtained by traditional technology, and virtually independent of the direction of the specimens building. Impact strength and elongation, conversely, differ almost two times. The surface has a viscous character of destruction for all the specimens. Analysis of the structure by EBSD method revealed texture presence and coinciding major axis of grains with building direction. Comparison of strength properties and structure parameters allows associating the anisotropy of mechanical properties with the anisotropy of the structure. These results are important for taking into account the anisotropy of the mechanical properties while designing a particular item.

Development of anisotropic contiguity in deforming partially molten aggregates: 1. Theory and fast multipole boundary elements method

AbstractThe microstructure of partially molten rocks strongly influences the macroscopic physical properties. Contiguity, a geometric parameter, is a tensorial quantity that describes the area fraction of intergranular contact in a partially molten aggregate. It is also a key parameter that controls the effective elastic strength of the grain network. As the shape of the grains evolves during deformation, so does the contiguity of each grain. In this article, we present the first set of numerical simulations of evolution of grain‐scale contiguity of an aggregate during matrix deformation using a fast multipole boundary elements method‐based model. We simulate a pure shear deformation of an aggregate of 1200 grains up to a shortening of 0.47 and a simple shear deformation of 900 grains up to a shear strain of 0.75, for solid‐melt viscosity ratios of 1 and 50. Our results demonstrate that the initially isotropic contiguity tensor becomes strongly anisotropic during deformation. We also observe that the differential shortening, the normalized difference between the major and minor axes of grains, is inversely related to the ratio between the principal components of the contiguity tensor. In pure shear, the principal components of the contiguity tensor remain parallel to the irrotational principal axes of the applied strain. In simple shear, however, the principal components of the contiguity tensor rotate continually during the course of deformation in this study. In the companion article we present the seismic anisotropy resulting from the anisotropic contiguity and the implications for the Earth's lithosphere‐asthenosphere boundary.

Activation of multiple twins by pre-tension and compression to enhance the strength of Mg–3Al–1Zn alloy plates

Abstract For basal textured Mg alloy plates, {10-12} twins can be easily generated by pre-compression perpendicular to the c -axis of grains. Thus, it should be practical to strengthen Mg alloy plates by introducing twin boundaries. In this study, we show that control of the a -axis distribution is also important for enhancing the strengthening effect by pre-inducing {10-12} twins. Pre-tension along rolling direction (RD) is applied on a rolled AZ31 Mg alloy plate, and then the sample is compressed along transverse direction (TD) to generate {10-12} twins. The experimental results show that pre-tension causes 〈10-10〉 orientations concentrating toward RD, which promotes the activation of multiple twin variants in each grain for subsequent compression along TD. As a consequence, twin nucleation rather than twin growth is favored, and the number of twin lamellae per grain is increased, which enhances the refinement hardening effect during compression of the twinned sample along RD. The underline mechanism is analyzed, which can also provide some insights into understanding deformation mechanism of Mg alloys.

The effects of equal channel angular extrusion on the mechanical and electrical properties of alumina dispersion-strengthened copper alloys

Two alloys of alumina dispersion-strengthened copper were subjected to 1-4 passes of equal channel angular extrusion (ECAE) by route BC. Microstructures before and after deformation were characterized by scanning electron microscopy, scanning ion microscopy and electron backscatter diffraction. Mechanical and electrical properties were evaluated using uniaxial tensile testing and the four point probe method, respectively. The initial microstructure consisted of cylindrical grains, elongated in the extrusion direction and highly textured in a <100>/<111> orientation. Following four ECAE passes, the average major axis of grains in both alloys decreased by over 50%, and the microstructure approached an equiaxed morphology. The texture decreased in intensity and shifted to a <112> orientation after one ECAE pass, followed by a transition to a <101> orientation by the fourth pass. Flow stress of AL-25 and AL-60 increased only 48MPa (10%) and 24MPa (5%), respectively, while the conductivity of both alloys remained essentially unchanged. A combination of Hall–Petch strengthening and texture softening are used to explain the observed changes in mechanical behavior.

Critical Current Properties of c-Axis Oriented Bi(Pb)2223 Bulks Sintered under High Gas Pressures

Abstract Enhancement of J c performance of Bi(Pb)2223 bulks was attempted by sintering under controlled over pressures (CT-OP) and c -axis grain orientation. Relative density of bulks increased up to 93% with an increase of total gas pressure during the sintering. In addition, improvement of grain coupling by CT-OP sintering was indicated from normal state resistivity. Reflecting these facts, the bulks sintered by the CT-OP method showed higher J c than the bulks sintered under ambient pressure. On the other hand, magnetic grain alignment technique was adopted to achieve c -axis grain orientation. The c -axis oriented bulks showed higher J c than randomly oriented bulks. The observed J c of 2.3 x 104 Acm-2 (20 K, 1 kOe) was very high value as for Bi(Pb)2223 sintered bulks.