Cuboidal Shape Research Articles

Omega phase transformation – morphologies and mechanisms

Abstract Various morphologies of the ω phase are observed in the α and the β phases of group-IV elements and their alloys where formation of this phase is induced by various means, namely, quenching from the β-phase field, isothermal annealing, under high static as well as dynamic pressure, and irradiation. The presence of various morphologies, such as ellipsoidal, cuboidal, granular or plate shapes, under different conditions is demonstrated. It is shown that various factors, including shuffling of atoms, shearing of atomic planes, long-range diffusion of solute atoms, change in volume during transformation, etc., influence the formation of different morphologies of the ω phase. The underlying mechanisms in each case are discussed. Ordered ω phases, which exist as equilibrium phases in various alloy systems, are shown as a case of superimposition of the concentration wave on the displacement wave.

A sharp-interface model for diffusional evolution of precipitates in visco-plastic materials

This paper describes a 3D implementation of the sharp-interface theory for material heterogeneities and is, hence, able to identify equilibrium shapes of precipitates in superalloys. The theory is adopted from Morton E. Gurtin and extended by crystal plasticity in the bulk. Crystal plasticity relaxes stresses at the phase interface, which leads to subsequent coalescence of the precipitates. The fully implicit model employs the extended finite element method (XFEM) in conjunction with level sets. The level set is advected in a velocity field computed by the stress-modified Gibbs-Thomson interface condition. Mechanical equilibrium and level set update are solved in a staggered procedure. Jump quantities are treated by means of a suitable enriched least square smoothing. Multiple schemes for the computation of curvature of surfaces in the context of the XFEM are presented and compared. Equilibrium shapes at different levels of misfit are computed. A cuboidal equilibrium shape is retrieved in a rotated mesh in order to quantify mesh-independence, a linear volume-time relationship during Ostwald ripening is reproduced and merging of particles under tension is reported.

Ferroelectric monodisperse Ln-doped barium titanate cuboidal nanocrystals prepared by a solvothermal route

We demonstrate here that the dielectric, electrical and optical properties of BaTiO3colloidal nanocrystals with a cuboidal shape can be modulated upon aliovalent doping with Ln3+rare earth ions (Ln = La3+, Ce3+, Nd3+, Sm3+, Gd3+, Dy3+, and Tm3+).

A Comparison of the Marginal Accuracy of Metal Copings Made with Three Different Brands of Nickel-Chromium Alloys and Various Sprue Designs: An Vitro Study.

Introduction:It is important to construct the sprue in a way that ensures that the mold gets an appropriate supply of metal at the right speed. Many manufacturers now offer sprue designs that have not been advocated in textbooks or publications for their normal use.Aim:The goal of this research was to compare the sprue design's marginal fit to that of the other designs.Methods:During this investigation, we attempted to see whether the fabrication of metal copings could be improved. Three sprue designs were used in this research for the assessment of casting accuracy: normal cylindrical, funnel-shaped, and cuboidal or flattened sprue forms.Results:The mean marginal disparity of nickel–chromium (Ni–Cr) alloy copings made by three distinct brands was determined to be statistically insignificant.Conclusion:Within the limitation of the study, it was concluded that the marginal accuracy of metal copings fabricated with three different brands of Ni–Cr alloy did not reveal a statistically significant result. However, out of the three different sprue designs, that is, cylindrical, cuboidal, and funnel shape, the marginal accuracy of cylindrical and cuboidal sprue designs was found to be better than that of the funnel shape sprue design because the funnel shape sprue design is narrow at the point of attachment, thereby increasing the flow pressure and decreasing the turbulence of the molten metal.

Green synthesis of silver nanoparticles using leaf extracts of Mentha arvensis Linn. and demonstration of their in vitro antibacterial activities

A study was carried out to synthesize silver nanoparticles (Ag-NPs) using plant extracts and to explore their pharmaceutical application as antibacterial agents. Dried leaves of Mentha arvensis Linn. were powdered and extracts were prepared using three different organic solvents. Preliminary screening on antibacterial activity by agar well diffusion method indicated that the methanolic extract possessed higher potential than the other two. Phytochemical analysis of the leaf extract revealed that it possesses tannins, steroids, terpenoids and flavonoids. Ag-NPs prepared using this extract were of spherical to cuboidal shape ranging in size from 40 to 70 nm. It retained essential chemical groups and had the required surface plasmon resonance. Further to the antimicrobial assay, the Ag-NPs, in contrast to the whole methanolic leaf extract, showed better (100% vs. 80%) bactericidal activity against the indicator organisms. The zones of growth inhibition for gram positive bacteria ranged between 14±0.6 and 23±0.3, while it was between 12±0.6 and 22±0.2 for gram negative bacteria. The Ag-NPs presented the minimum inhibitory concentration values of 250 µg/mL for gram positive bacteria and 250 - 500 µg/mL for gram negative bacteria. These findings suggest that the natural compounds present in M. arvensis L. possess the potency to facilitate the synthesis and antibacterial action of Ag-NPs.

Influence of deep cryogenic treatment on natural and artificial aging of Al-Mg-Si alloy EN AW 6026

This paper discusses the effect of deep cryogenic treatment (DCT) on the evolution of natural and artificial aging of Al-Mg-Si alloy EN AW 6026. This study provides the first research and evidence of DCT effect on dispersoids and their development in aluminum alloys. DCT induces reformation and regrowth of dispersoids during natural aging from a preferential cuboidal shape to spherical, which is also distinguishable by the change in chemical composition. Additionally, with DCT the dispersoids form in a denser manner, which consequently influences the hardness evolution with aging time. The study also reveals that the exposure duration to DCT (from 24 to 48 h) increases the DCT impact on the hardness evolution during natural aging of selected alloy. The influence of homogenization temperature on the DCT performance is also researched in connection to modified natural aging, which is correlated to the presence and formation of secondary phases during homogenization. Furthermore, DCT also promotes the formation of β'' precipitates and at the same time retards the formation of larger β' precipitates during artificial aging. After artificial aging, both dispersoids and precipitates display a denser population and more elongated shape aligned along the< 100 > axis of the aluminum matrix with DCT compared to conventionally heat-treated samples without DCT. The microstructural changes during DCT application are strongly linked to the modification of dispersoids with homogenization and artificial aging that influence the content of alloying elements in the matrix.

Durability Investigation of Sulfur and Traditional Concrete within Aggressive Environments

An experimental study was conducted to evaluate durability (compressive strength and mass loss%) in the modified sulfur concrete within aggressive environments. The modified sulfur concrete was prepared by adding recycled polymeric and filler materials that showed a noticeable enhancement for modified sulfur concrete characteristics. A durability comparison between modified sulfur concrete and traditional concrete was investigated at normal and aggressive environments (10% HCl and 3% NaCl). A cuboid shape with size (50 × 50 × 50mm) was used in this research to investigate the durability of both modified sulfur and traditional concrete. The modified sulfur concrete characteristics revealed high stable structure than traditional due to preventing a process of crystallization of sulfur that modified with polymer and fillers. The compressive strength was 10.87 – 22.5% increased for modified sulfur concrete compared to the traditional concrete at the normal environment. In the aggressive environments, the modified sulfur concrete illustrated high resistance strength compared to the traditional concrete. The comparison revealed a significant impact for 10% HCl and 3% NaCl on the traditional concrete. The compressive strength decreased between (88.78 – 96.17) % for traditional concrete compared to modified sulfur concrete in 10% HCl solution and (84.25 – 95.06) % in 3% NaCl solution. Furthermore, mass loss % of the modified sulfur concrete indicated high resistance compared to the traditional concrete in both 10% HCl and 3% NaCl solutions.

Requirements for investigation of physical/mechanical properties of rocks and crushed stone quality in Russia

The industry of nonmetallic building materials is a priority industry that determines the current state of the national economy of Russia and the potential for its development. The requirements for the quality of crushed stone are constantly increasing. At the same time, the history of the emergence and development of these requirements has not been studied in the literature. An analysis of historical experience is necessary to identify the patterns of development of technology for the production of road crushed stone and to work out an effective way of development at the present stage. The article studies genesis of requirements for the research of the physical and mechanical properties of rocks and the quality of road crushed stone in Russia. This study is the first system-based and comprehensive study on this topic. The chronological framework of the study is limited to the beginning of the 19th century&mdash;the time of the appearance of highways in Russia, and at the turn of the 19th&ndash;20th centuries as a period of the emergence of vehicles and the development of requirements for the quality of crushed stone. The article shows that construction of highways necessitated studies into properties of rocks. Russian specialists started from the experience gained in European countries. However, Russian engineers did not copy European experience. They supplemented and developed European experience taking into account Russian realities. It was found that the main indicators of the quality of crushed stone were its strength (resistance to compressive), abrasion and impact loads, grain size, grain size distribution, cuboid shape and contamination with foreign impurities. These indicators are basic in all modern GOSTs (All-Union State Standard) and regulatory documents that regulate the quality of crushed stone. In the same period, methods of determining the quality indicators of crushed stone in laboratory conditions were proposed. The principles underlying these methods, in fact, correspond to modern methods of testing the physical and mechanical properties of rocks. The difference lies in the hardware, experimental conditions and quantitative assessment of the determined indicators.

Microstructure evolution and phase transformation in a nickel-based superalloy with varying Ti/Al ratios: Part 1 - Microstructure evolution

Nickel-based superalloy Waspaloy is a promising candidate material applied in power plant components for higher operation temperatures. Trial alloys based on Waspaloy with varying Ti/Al ratios (2.14, 1.44 and 0.74) were produced. The microstructure evolution, mainly focusing on strengthening phase γ’ and grain boundary carbides, were investigated and compared in these alloys during thermal exposure at 800 °C for up to 10,000 h. It is observed that lowering Ti/Al ratio leads to slight smaller average γ’ size and higher volume fraction of γ’. Moreover, γ’ in samples with low ratios kept spherical morphologies after long-term ageing compared to high ratio samples, which transformed to cuboidal shape in later ageing stage due to higher lattice misfit. A clear M23C6 carbides coarsening at grain boundary and growth toward grain interior in lower ratio samples were also observed during ageing process. The results showed higher thermal stability of lower ratio samples in terms of γ’ morphology and volume fraction evolution. This was reflected by the slightly higher hardness values in lower ratio samples in later ageing stages.

Experimental Investigation of Heat Transfer with Natural Convection of Non-Newtonian Fluid Inside the Enclosure with Hot Obstacle

In this study, heat transfer utilizing non-Newtonian fluids with a power-law model in a rectangular enclosure containing a hot obstacle was verified experimentally. The impact of aspect proportion (AR) on fluid flow characteristics and heat transfer, obstacle shapes, and various amounts of carboxymethylcellulose was explored with distilled water which in turn controls the index of powers-law (n). The findings show that the increases in the Number of Rayleigh, lead to the greater the Number of Nusselt, and the greater the non-Newtonian behavior, increased the heat transfer. There is also a noticeable impact when changing the shape of an obstacle on heat transfer as the cylindrical shape enhances heat transfer greater than the cuboid shape. As for aspect proportion, it also affects heat transfer inversely.

The Osteogenic Differentiation of Human Dental Pulp Stem Cells through G0/G1 Arrest and the p-ERK/Runx-2 Pathway by Sonic Vibration.

Mechanical/physical stimulations modulate tissue metabolism, and this process involves multiple cellular mechanisms, including the secretion of growth factors and the activation of mechano-physically sensitive kinases. Cells and tissue can be modulated through specific vibration-induced changes in cell activity, which depend on the vibration frequency and occur via differential gene expression. However, there are few reports about the effects of medium-magnitude (1.12 g) sonic vibration on the osteogenic differentiation of human dental pulp stem cells (HDPSCs). In this study, we investigated whether medium-magnitude (1.12 g) sonic vibration with a frequency of 30, 45, or 100 Hz could affect the osteogenic differentiation of HDPSCs. Their cell morphology changed to a cuboidal shape at 45 Hz and 100 Hz, but the cells in the other groups were elongated. FACS analysis showed decreased CD 73, CD 90, and CD 105 expression at 45 Hz and 100 Hz. Additionally, the proportions of cells in the G0/G1 phase in the control, 30 Hz, 45 Hz, and 100 Hz groups after vibration were 60.7%, 65.9%, 68.3%, and 66.7%, respectively. The mRNA levels of osteogenic-specific markers, including osteonectin, osteocalcin, BMP-2, ALP, and Runx-2, increased at 45 and 100 Hz, and the ALP and calcium content was elevated in the vibration groups compared with those in the control. Additionally, the western blotting results showed that p-ERK, BSP, osteoprotegerin, and osteonectin proteins were upregulated at 45 Hz compared with the other groups. The vibration groups showed higher ALP and calcium content than the control. Vibration, especially at 100 Hz, increased the number of calcified nodes relative to the control group, as evidenced by von Kossa staining. Immunohistochemical staining demonstrated that type I and III collagen, osteonectin, and osteopontin were upregulated at 45 Hz and 100 Hz. These results suggest that medium magnitude vibration at 45 Hz induces the G0/G1 arrest of HDPSCs through the p-ERK/Runx-2 pathway and can serve as a potent stimulator of differentiation and extracellular matrix production.

Influence of Magnetite Nanoparticles Shape and Spontaneous Surface Oxidation on the Electron Transport Mechanism.

The spontaneous oxidation of a magnetite surface and shape design are major aspects of synthesizing various nanostructures with unique magnetic and electrical properties, catalytic activity, and biocompatibility. In this article, the roles of different organic modifiers on the shape and formation of an oxidized layer composed of maghemite were discussed and described in the context of magnetic and electrical properties. It was confirmed that Fe3O4 nanoparticles synthesized in the presence of triphenylphosphine could be characterized by cuboidal shape, a relatively low average particle size (9.6 ± 2.0 nm), and high saturation magnetization equal to 55.2 emu/g. Furthermore, it has been confirmed that low-frequency conductivity and dielectric properties are related to surface disordering and oxidation. The electric energy storage possibility increased for nanoparticles with a disordered and oxidized surface, whereas the dielectric losses in these particles were strongly related to their size. The cuboidal magnetite nanoparticles synthesized in the presence of triphenylphosphine had an ultrahigh electrical conductivity (1.02 × 10−4 S/cm at 10 Hz) in comparison to the spherical ones. At higher temperatures, the maghemite content altered the behavior of electrons. The electrical conductivity can be described by correlated barrier hopping or overlapping large polaron tunneling. Interestingly, the activation energies of electrons transport by the surface were similar for all the analyzed nanoparticles in low- and high-temperature ranges.

Study on Effect of Rail Filet Radius in Electromagnetic Railgun

Enhancing the inductance gradient of an electromagnetic railgun (EMRG) directly translates to an improvement in the force on the projectile. Fileting the rails on one side is one of the ways to improve the inductance gradient. This work focuses on the effects of filet arc radius on different parameters of inductance gradient, current density distribution, magnetic flux density, barrel efficiency, breech energy, and critical velocity. The performance of rails with filet arc radius of 2, 4, and 6 mm are compared with the conventional cuboid shape rail geometry. Dynamic field distributions are analyzed by simulating the designed systems in LS-DYNA. A magneto-static analysis is performed using Ansys-Maxwell to determine the magnetic flux density produced behind the armature. It is observed that there is an increase in the flux density and barrel efficiency when filet radius increases. An improvement of 3.81% is observed in the flux density and the barrel efficiency improved from 24% in conventional rails to 27% in rails with a filet radius of 6 mm.

Ligand-Assisted Growth of Nanowires from Solution

We consider the development of ligand-assisted growth processes for generating shape-anisotropic nanomaterials. Using statistical mechanics, we analyze the conditions under which ligand-assisted growth of shape-anisotropic crystalline nanomaterials from solution can take place. Depending on ligand-facet interaction energy and crystal facet area, molecular ligands can form compact layers on some facets leaving other facets free. The growth process is then restricted to free facets and may result in significant anisotropy in crystal shape. Our study uncovers the conditions for ligand-assisted growth of nanoplatelets and nanowires from isotropic or anisotropic seed nanocrystals of cuboid shape. We show that in contrast to nanoplatelets, ligand-assisted growth of nanowires requires certain anisotropy in the ligand-facet interaction energy.

Multicomponent perovskite superlattices

Multicomponent perovskite superlattices

Unsupervised learning for cuboid shape abstraction via joint segmentation from point clouds

Unsupervised learning for cuboid shape abstraction via joint segmentation from point clouds

Effects of aging treatment on the evolution of precipitated phase in CoCrFeNiTi0.6 high entropy alloys

In this study, the effect of aging time on the microstructure of precipitates in a face-centered cubic (FCC) CoCrFeNiTi0.6 high-entropy alloy (HEA) was investigated. The microstructure of precipitates was analyzed by SEM and TEM. The results showed that the CoCrFeNiTi0.6 alloy exhibited a typical dendritic structure, whose phase consisted of an ordered FCC solid-solution matrix (nanoscale L12-(Ni, Co)3Ti type particles) and intermetallic phases at 900 °C for different aging times. Meanwhile, the intermetallic compounds were composed of (Cr, Fe)-rich σ phases with a tetragonal structure and (Ni, Ti)-rich η phase with a long period stacking ordered (LPSO) structure. Additionally, the influence of aging time on the shape and structure of γ' precipitates was revealed. It was noticeable that the morphological transformation of nanoscale γ' precipitates evolved from an initially spheroidal to spheroidal-like shapes, following cuboidal-like shapes with flat edges, and finally, γ' precipitates with cuboidal shape were formed simultaneously with the appearance of the split with increasing aging time. Furthermore, the morphological evolution of γ' precipitates was quantitatively analyzed using a characteristic parameter's value of precipitates based on lattice misfit between the matrix and precipitates. This research would provide guidance for designing the precipitate structure in the L12-strengthened HEA and facilitate to establish the relationships between the microstructure of the precipitates and properties.

Unsupervised learning for cuboid shape abstraction via joint segmentation from point clouds

Representing complex 3D objects as simple geometric primitives, known as shape abstraction, is important for geometric modeling, structural analysis, and shape synthesis. In this paper, we propose an unsupervised shape abstraction method to map a point cloud into a compact cuboid representation. We jointly predict cuboid allocation as part segmentation and cuboid shapes and enforce the consistency between the segmentation and shape abstraction for self-learning. For the cuboid abstraction task, we transform the input point cloud into a set of parametric cuboids using a variational auto-encoder network. The segmentation network allocates each point into a cuboid considering the point-cuboid affinity. Without manual annotations of parts in point clouds, we design four novel losses to jointly supervise the two branches in terms of geometric similarity and cuboid compactness. We evaluate our method on multiple shape collections and demonstrate its superiority over existing shape abstraction methods. Moreover, based on our network architecture and learned representations, our approach supports various applications including structured shape generation, shape interpolation, and structural shape clustering.

Microstructures and Mechanical Properties of Al-Ti-Zr-Nb-Ta-Mo-V Refractory High-Entropy Alloys with Coherent B2 Nanoprecipitation

In this work, the microstructural evolution and mechanical properties of new body-centered cubic (BCC)-based Al-Ti-Zr-Nb-Ta-Mo-V refractory high-entropy alloys (RHEAs) with coherent B2 precipitation are investigated. These designed alloy ingots were solid-solutionized at 1573 K for 2 h and then aged at 873 K for 24 h, in which each treatment was followed by water quenching. It was found that there exists phase separation of BCC matrix, Ti/Zr-rich BCC1 and Nb/Ta-rich BCC2 in these alloys. Moreover, ultra-fine spherical B2 nanoparticles with a size of 3~5 nm were dispersed in BCC2 matrix. These B2 nanoparticles could be coarsened up to 25~50 nm after aging and the particle morphology also changes to a cuboidal shape due to a moderate lattice misfit (ε = 0.7~2.0%). Also, Zr5Al3 phase could coexist with the B2 phase, where the difference between them is that the Ti element is enriched in B2 phase, rather than in Zr5Al3. Among them, the solutionized Al2Ti5Zr4Nb2.5Ta2.5 RHEAs exhibit good compressive mechanical property with a high yield strength of 1240 MPa and a large plasticity, which is mainly attributed to the coherent precipitation in the BCC matrix.

Understanding the microstructural stability in a γ′-strengthened Ni-Fe-Cr-Al-Ti alloy

Ni-Fe-Cr-Al-Ti alloys, with Ni levels of about 45 at% have the potential to develop a microstructure consisting of a face-centered cubic (γ) matrix with homogeneously precipitated, nanoscale ordered γ′ precipitates similar to that found in traditional Ni-based superalloys with a significantly greater Ni content. Scanning electron microscopy, transmission electron microscopy, atom probe tomography, and CALPHAD-based thermodynamic modeling were employed to determine the phase stabilities and microstructural evolution in an age-hardenable 44.56Ni-26.6Fe-19.2Cr-1.0Co-3.4Al-4.4Ti-0.7Mo-0.14 C (at%) alloy. The primary heat treatment of solution annealing at 1121 °C for 4 h followed by age-hardening at 760 °C for 16 h resulted in a microstructure consisting of fine γ′ precipitates in an austenitic matrix along with grain boundary precipitates of carbides and other minor phases. Long-term aging at 900 °C for 250 h resulted in the coarsening of γ′ precipitates along with a change in the morphology from an initial spherical to a more cuboidal shape. In addition, the formation of plate-like η phase precipitates was observed, concomitant with the partial dissolution of the γ′ phase. The ability of computational thermodynamic models to predict microstructural characteristics is discussed.