Preferred Crystallographic Planes Research Articles

Significance of separations occurring in mechanical testing of thermomechanical rolled pipeline steels

In this study, the origin of separations is investigated in modern high strength pipeline steels. In-depth microstructure characterization and property correlation is used to demonstrate that preferred crystallographic planes are responsible for the generation of separations in thermomechanical rolled steels with high cleanliness. Further insights on the influence of crystallographic orientation are obtained by performing different types of standard and non-standard tests with specific specimen and notch orientations and evaluating the related crack propagation path. Finally, special texture components are identified, which determine whether in-plane fracture, splitting or deflection of the cleavage parts take place. This study assists in understanding the separation phenomenon in modern high strength pipeline steels across the different test methods. Furthermore, it amplifies that the separations in thermomechanical rolled steels with high steel cleanliness are inherently linked to the orientation of specific crystallographic planes and are not necessarily an indication of a poor material behavior.

Influence of xylenol orange dye on structural, vibrational, thermal and luminescence properties of TGS crystals

Dye can induce positive change in crystal. Pure and xylenol orange-dyed triglycine sulphate (TGS) large single crystals (> 14 cm2) were grown by solution technique in which dye inclusion pattern along preferred crystallographic planes were visible. Rietveld refinement was used to confirm monoclinic phase with space group P21 in XRD analyses. The crystallite size of both grown crystals were calculated by Scherrer method. In FTIR and Raman analyses, all the observed functional groups were explained. Thermal stability of dyed TGS crystal was increased. UV–Vis–NIR spectra showed that grown crystals were highly transparent with the lower cut off at 230 and 228 nm for pure and dyed crystals, respectively. The characteristics luminescence properties, including hyperluminescence and additional luminescence nature in dyed crystal, were explained. Pure TGS fell in violet region which shifted in blue region in CIE diagram after dyeing. Changes in PL, Raman, UV–Vis and thermal behavior due to dye doping established the TGS crystal as a better candidate for optical applications.

A Thermodynamically Favored Crystal Orientation in Mixed Formamidinium/Methylammonium Perovskite for Efficient Solar Cells.

Crystal orientation has a great impact on the properties of perovskite films and the resultant device performance. Up to now, the exquisite control of crystal orientation (the preferred crystallographic planes and the crystal stacking mode with respect to the particular planes) in mixed-cation perovskites has received limited success, and the underlying mechanism that governs device performance is still not clear. Here, a thermodynamically favored crystal orientation in formamidinium/methylammonium (FA/MA) mixed-cation perovskites is finely tuned by composition engineering. Density functional theory calculations reveal that the FA/MA ratio affects the surface energy of the mixed perovskites, leading to the variation of preferential orientation consequently. The preferable growth along the (001) crystal plane, when lying parallel to the substrates, affects their charge transportation and collection properties. Under the optimized condition, the mixed-cation perovskite (FA1- x MAx PbI2.87 Br0.13 (Cl)) solar cells deliver a champion power conversion efficiency over 21%, with a certified efficiency of 20.50 ± 0.50%. The present work not only provides a vital step in understanding the intrinsic properties of mixed-cation perovskites but also lays the foundation for further investigation and application in perovskite optoelectronics.

Effect of Annealing Atmosphere on the Structural and Optical Properties of ZnO Thin Films on Si (100) Substrates Grown by Atomic Layer Deposition

ZnO thin films were deposited on Si (100) substrates by atomic layer deposition. Annealing treatments for the as-deposited films were performed in nitrogen, oxygen, argon and air at 800 °C, respectively. The influence of annealing atmosphere on the structural and optical properties of the ALD-ZnO thin films was investigated by XRD, SEM, and PL. Results reveals that the films annealed in oxygen atmosphere exhibited excellent crystallinity (polycrystalline hexagonal wurtzite structure with a strong (002) preferred crystallographic planes), relatively smooth surface and better luminescence performance, which means that O2 is the most suitable annealing atmosphere for obtaining high quality ALD-ZnO thin films.

Plastic deformation treated as material flow through adjustable crystal lattice

Looking at severe plastic deformation experiments, it seems that crystalline materials at yield behave as a special kind of anisotropic, highly viscous fluids flowing through an adjustable crystal lattice space. High viscosity provides a possibility to describe the flow as a quasi-static process, where inertial and other body forces can be neglected. The flow through the lattice space is restricted to preferred crystallographic planes and directions causing anisotropy. In the deformation process the lattice is strained and rotated. The proposed model is based on the rate form of the decomposition rule: the velocity gradient consists of the lattice velocity gradient and the sum of the velocity gradients corresponding to the slip rates of individual slip systems. The proposed crystal plasticity model allowing for large deformations is treated as the flow-adjusted boundary value problem. As a test example we analyze a plastic flow of an single crystal compressed in a channel die. We propose three step algorithm of finite element discretization for a numerical solution in the Arbitrary Lagrangian Eulerian (ALE) configuration.

Influence of annealing atmosphere on the structure, morphology and transmittance of N-incorporated Ga2O3 films

N-incorporated Ga2O3 films were deposited on sapphire substrates by radio frequency magnetron sputtering. Annealing treatments for the as-deposited samples were performed in nitrogen, oxygen and air at 800°C, respectively. The effect of annealing atmosphere on the structure, morphology and transmittance of the as-deposited films was investigated. X-ray diffraction (XRD) patterns of the as-deposited and annealed films exhibited monocline crystal structure with a strong (−402) preferred crystallographic planes. Annealing atmosphere greatly affected the surface morphology and transmittance of N-incorporated Ga2O3 films. Annealing in nitrogen exhibited excellent crystallinity, smooth surface and higher transmittance in visible range. Moreover, the red shift of the band gap was observed after annealing.

High-voltage spinel cathodes for lithium-ion batteries: controlling the growth of preferred crystallographic planes through cation doping

The high-voltage LiMn1.5Ni0.5O4 spinel cathode has become appealing for lithium-ion batteries as it offers fast, 3-dimesional Li-ion diffusion and high power. However, its commercialization is hampered by capacity fade during cycling due to the aggressive reaction between the cathode surface and the electrolyte and dissolution of the active material under the high-voltage operating conditions. We present here an investigation of the nucleation and growth of doped co-precipitated mixed-metal hydroxide precursor particles, and the resulting stabilization of preferred crystallographic surface planes in the final spinel samples. The samples are synthesized by a coprecipitation reaction of the mixed-metal hydroxide precursors with a scalable continuously stirred tank reactor (CSTR), followed by firing with lithium hydroxide. The synthesized samples are characterized by X-ray diffraction, electron microscopy, time-of-fight – secondary ion mass spectroscopy (TOF-SIMS), and electrochemical charge–discharge measurements. It is found that doping with certain cations stabilizes the growth of low-energy (111) surface planes, facilitating a long cycle life and fast high-rate performance.

Nanoindentation studies of titanium single crystals

Titanium single crystal planes of different atomic density have been reported to show different oxidation characteristics. The differences in oxide characteristics have further been demonstrated to lead to differences in osteoblast attachment. Investigations of the preferred crystallographic planes of titanium for osteoblast attachment can be used to optimize the surfaces of single crystal and polycrystalline titanium implants for anchoring various prostheses. Nanoindentation techniques were used to determine mechanical properties of two crystallographic planes of titanium of different atomic density. Modulus of elasticity of 128±10 GPa was obtained for polycrystalline titanium and 123±5 and 124±6 GPa for the basal plane and pyramidal planes, respectively. The variation of modulus with crystal orientation was not greater than the statistical variation in the data. Surface hardness values were 2.1±0.1 GPa for the polycrystalline sample and 1.6±0.1 and 1.9±0.1 GPa, respectively, for the basal and pyramidal planes. Curves of hardness as a function of depth (0–2000 nm) obtained from electrochemically polished surfaces showed a sharp increase at shallow depths and may reflect changes caused by oxidation of the titanium surfaces.

Subboundary Characterization and Creep Deformation in Investment Cast Ti-48Al-2Nb-2Cr

AbstractSubgrain boundaries (subboundaries) in a creep deformed investment cast Ti-48Al-2Nb-2Cr specimen were characterized. A multi-stress drop test was performed at temperature 765 °C and stresses from 276 MPa to 103 MPa. The stress exponent n = 7. Subboundaries were observed both in equiaxed γ grains and within γ laths in lamellar grains. Dislocations within the subboundaries are characterized to be ordinary 1/2<110] dislocations. Subboundaries are found to occur on many crystallographic planes and no preferred crystallographic planes are found for subboundary formation in the crept TiAl specimen. Misorientations across the subboundaries are less than 1°. Analysis of subboundary formation mode indicates that the creep deformation in TiAl is pure metal type.

Oxygen effects on the corrosion of niobium and tantalum by liquid lithium

The effect of oxygen on the corrosion of niobium and tantalum by liquid lithium at 600°C was studied with static capsules. An increase in the oxygen concentration of the lithium from 100 to 2000 ppm had no measurable effect on the dissolution of either refractory metal. Exposure to lithium reduced the oxygen content of niobium and tantalum to less than or equal to 20 ppm regardless of the oxygen concentration of the lithium, results that agree with thermodynamic calculations. When the initial oxygen concentration of niobium and tantalum exceeded a threshold level, lithium (with no oxygen added) penetrated the refractory metal. Penetration resulted from the formation of a ternary oxide on grain boundaries or preferred crystallographic planes and proceeded by a wedging mechanism, which is caused by stresses generated by the corrosion product. Penetration was along grain boundaries at low oxygen concentrations, the attack depth and number of affected boundaries increasing with increasing oxygen concentration. At higher oxygen concentrations, transgranular attack also occurred. The threshold oxygen concentrations for attack were 400 and 100 ppm for niobium and tantalum, respectively.

Hydrothermal and flux growth of zircon crystals

Attemps to grow single crystals of zircon (ZrSiO4) by flux and hydrothermal techniques are described. Crystals grown from a lithium tungstate melt were colored yellow brown in corners indicating absorption of a growth impurity along preferred crystallographic planes. The impurity is suspected to be iron reported in the lithium tungstate flux. Hydrothermal zircon growth was accomplished using a 3 molar aqueous KF mineralizer at about 30000 psi and 500°C. The nutrient used was ZrO2 and SiO2 powders pressed at 30 000 psi and sintered at 1520°C. Due to the relatively low solubility of zircon in various molten salts, the hydrothermal method appears to be more suitable than the flux method for growing large single crystals of zircon.

Overvoltage and diffusion through iron and palladium

Observations are recorded on X-ray spectra diffracted from cathodes of iron and palladium during actual discharge and diffusion of hydrogen. For iron, no expansion of the crystal lattice greater than 0.0002 Å could be observed during such diffusion, and the broadening observed of X-ray diffraction spectra indicated no preferred crystallographic planes for the evolution of molecular hydrogen. Blisters were formed across the faces of single crystals of iron, when made a cathode, indicating that diffusion of hydrogen occurs through the crystal grains rather than along crystal boundaries. For palladium, an expansion was observed during actual electrolysis to an extent of 0.0170 + 0.0002 Å. On ceasing electrolysis, there was reversion to a less-expanded lattice of palladium hydride. Broadening of the reflexions observed during electrolysis indicated no preferred planes for evolution of hydrogen. The significance of these findings is discussed for mechanisms of overvoltage and of diffusion of hydrogen through metals.