Crystals Of Various Orientations Research Articles

Dependence of the ZrO2 growth on the crystal orientation: growth simulations and magnetron sputtering

The growth of crystalline ZrO2 is studied by a combined approach of atom-by-atom growth simulations, high-power impulse magnetron sputtering and conventional pulsedmagnetron sputtering. We focus on the energy of arriving atoms of various elements, and investigate how does it affect the growth of ZrO2 crystals of various orientations. Theresults are correlated with quantities such as surface energy and horizontal periodicity of individual orientations. Simulations show that the growth of orientations characterized by high surface energy and short horizontal period, (001)in the first place, requires higher energy delivered by arriving atoms, and that the energy is more effectively delivered by heavy Zr than by light O. Experiments confirm that the relative preference of such orientations increases with increasing substrate bias voltage, increasing concentration of ions which are subsequently accelerated by the bias voltage, and synchronization of the pulsed bias voltage with the arrival of heavy Zr+ ions. The results are important for the preparation of crystalline ZrO2 of various orientations for various technological applications, and the fundamental reasons behind them make them relevant also for the growth of other crystalline materials.

A Generalization of the von Mises Criterion for a Single Crystal with a Hexagonal Crystal Lattice

A natural generalization of the von Mises flow criterion is obtained taking into account anisotropy on single-crystal materials with a hexagonal crystal lattice. Boundary-value problems are posed for plane deformation by compression with back pressure, for uniaxial tension, compression, and for pure shear. A special case of solving boundary value problems for hexagonal magnesium with a purity of 99.9% at room temperature is considered. The values of coefficients included in the fluidity function and their errors are determined. The calculated and experimental data σ0.2% for magnesium single crystals of various orientations are compared.

Magnetoelectric effect in FeCo/PMN-PT/FeCo trilayers prepared by electroless deposition of FeCo on PMN-PT crystals with various orientations

The magnetoelectric (ME) effect was studied in the FeCo/PMN-PT/FeCo trilayer composites prepared by electroless deposition of the FeCo layers on the single crystal PMN-PT substrates with various crystal cuts. X-ray diffraction reveals that the orientation of PMN-PT substrate has no effect on the growth of FeCo layer. The structures with PMN-PT crystals of various orientations have different acoustic resonance frequencies. FeCo/PMN-PT/FeCo composites with PMN-PT of 〈001〉L×〈01‾1〉W×〈011〉T crystal cut shows superior ME performance, which is due to the highest piezoelectric module of PMN-PT.

Measuring the influence of magnesium on the elastic anisotropy of aluminum using in situ neutron diffraction

Comparison of lattice strains in crystals of various orientations is a primary method of validating polycrystal plasticity simulations. These strains can be measured using in situ neutron diffraction experiments while the corresponding information can be extracted from the simulation results. If the single crystal elastic moduli—particularly the anisotropy of the moduli with respect to lattice direction—are not accurately known, simulations cannot provide a favorable comparison to experiments. Previous work simulating deformation of an aluminum alloy with significant magnesium content (AA-5182) revealed that consistency with the experiments required a higher degree of anisotropy in the elastic moduli in the finite element simulations than that typically reported for pure aluminum. We undertook the current research to determine if the magnesium content causes that larger single crystal elastic anisotropy. Using in situ loading, we measured lattice strains and determined diffraction moduli of materials cove...

High temperature deformation and extended plasticity in Mg single crystals

The high temperature deformation behavior of Mg single crystals was precisely investigated using orientation imaging microscopy. For this purpose, Mg single crystals of various orientations were tensile tested in vacuum at temperatures between 473 and 673 K. A strain rate of 4.2 × 10−4 s−1 was employed. The elongations to fracture depended strongly on crystal orientation, the lowest fracture strains being associated with multiple slip. Single crystals in which single slip was activated exhibited extended ductilities corresponding to more than 1.5 in true strain. The strong orientation dependence of the ductility can also be correlated with the ease of occurrence of dynamic recrystallization (DRX), which took place in the multiple-slip specimens. The role of twinning in the initiation of DRX is also discussed.

Analysis of thermally activated formation and breakdown of Kear-Wilsdorf barriers in Ni3Ge single crystals of various orientations

The orientation dependence of the yield stress in Ni3Ge single crystals has been examined both theoretically and experimentally. The positive temperature dependence of the yield stress in the low temperature region is attributed to formation of Kear-Wilsdorf barriers. The forces driving the formation and breakdown of barriers are calculated within the framework of the Hirsch scheme. A distinctive feature of the model proposed is that the barrier is considered on the screw component of the a/2[ $${a \mathord{\left/ {\vphantom {a 2}} \right. \kern-\nulldelimiterspace} 2}\left[ {\bar 101} \right]\left( {111} \right)$$ 01](111) superdislocation in the primary octahedral plane. The major role in barrier formation belongs to anisotropy of elastic moduli, energy of antiphase boundaries in the octahedral plane, shear stresses in the cubic and octahedral planes, and friction-induced stress in the cubic plane. A comparison of predicted values of the driving force of barrier formation and breakdown with experimental values reveals their good agreement. An analysis of the orientation dependence of the driving force of barrier formation in the temperature range T = 77–293 K shows that the dependence Δ $$ \tau $$ (T) has an extremum for crystals deformed along the [ $${a \mathord{\left/ {\vphantom {a 2}} \right. \kern-\nulldelimiterspace} 2}\left[ {\bar 101} \right]\left( {111} \right)$$ 39] crystallographic direction, which is confirmed experimentally.

Quantitative determination of secondary slip in copper single crystals deformed in tension

To determine the amount and type of secondary slip, the full deformation matrix was calculated from current orientation and shape measurements at successive strain intervals for copper crystals of various orientations deformed in tension at room temperature. The data for diverse orientations within the standard triangle are remarkably similar and represent a combination of response to internal stress and applied stress. Internal stress due to primary edge dislocations is relieved by the same combination of secondary shears in all orientations, two particular Lomer–Cottrell reactions plus a shear on the cross-glide plane giving zero residual stress. Analogous sets of shears occur to relieve internal stresses arising from conjugate glide after overshoot ends, and coplanar glide in orientations close to [111]–[110]. This type of slip, not visible at the surface, is termed microscopic secondary slip. Deviations from this microscopic secondary glide are always in the direction of applied stress. Except for the special case of positive and negative cross-slip, secondary slip lines visible at the surface, termed slip-line slip, represent slip occurring in response to applied stress.

Stress Distribution in a Slip Trace of Deformed Ni3Ge Single Crystals

The shear‐stress distribution produced by distortion of Ni3Ge single crystals under compression is studied. The evolution of the dislocation structure during deformation of Ni3Ge single crystals of various orientations ([2¯34], [1¯11]$, [1¯39], and [001]) at T = 77, 293, 523, 673, and 873 K is analyzed. It was found that, up to failure strains, the dislocation structure is characterized by a uniform dislocation distribution. Regardless of the strain‐axis orientation, the linear relation τ = f(ρ0.5) is valid for all the test temperatures except for T = 77 K. The deviation from the linear relation at T = 77 K is due to the suppressed thermally activated slip of dislocations in nonuniform‐strain fragments at the specimen edges. In these fragments, the shear stresses are substantially reduced, and hence, the stresses produced by the dislocation cluster retard the development of slip in this trace.

Orientation dependence of the ferroelectric and piezoelectric behavior of Ba(Ti1−xZrx)O3 single crystals

The dielectric properties, ferroelectric polarization, and piezoelectric strain behavior of Ba(Ti1−xZrx)O3 (x=0.05 and 0.08) single crystals are studied for different crystal orientations. The study of dielectric properties suggests that the three phase transitions in BaTiO3 are pinched by substituting Ti with Zr but the anisotropic dielectric behavior is present in crystals of various orientations. The remnant polarization and strain behavior are also studied for different crystal directions. Higher strain and lower polarization are obtained along the pseudocubic 〈001〉 direction compared to those observed along the 〈110〉 and 〈111〉 directions in both orthorhombic (x=0.05) and rhombohedral (x=0.08) phase. The results for the 〈001〉 oriented orthorhombic crystals with x=0.05 indicate the highest strain level (∼0.25%) with almost hysteresis-free behavior and high piezoelectric coefficient (d33=500 pC/N).

The effects of sulfuric acid on the mechanical properties of ice single crystals

AbstractIce single crystals of various orientations containing various concentrations of H2SO4 up to 11.5 ppm were cut from large pucks of laboratory-grown ice. Constant-strain-rate compression tests were performed on the doped ice crystals both at −20°C at an axial strain rate of 1 × 10−5 s−1 and at −10°C at 1 × 106 s−1. The stress–strain curves showed a linearly rising stress with increasing strain, followed by a sharply declining stress after reaching a peak. With further strain, the sharp decline in stress slowed. The tests clearly showed, for the first time, that this naturally occurring impurity dramatically decreases both the peak stress and the subsequent flow stress of ice single crystals. The decrease in the peak strength was related to the square root of the concentration of H2SO4 up to 11.5 ppm, suggesting that the solubility limit of H2SO4 in ice is at least 11.5 ppm. The sulfuric acid also appeared to increase the ductility of the ice. Preliminary examination of a doped ice single crystal by synchrotron X-ray topography suggested that sulfuric acid dramatically increases the grown-in dislocation density.

A channeling investigation of the structural modifications in uranium dioxide submitted to swift-ion irradiation and aqueous corrosion

This paper presents a study of the influence of swift-heavy-ion irradiation on the behavior of UO 2 towards aqueous corrosion. Single crystals of various orientations are irradiated with 340-MeV Xe ions and subsequently leached in deionized water at 180°C. The channeling technique is used to quantify the structural modifications induced by both irradiation and leaching. The U and O sublattices are investigated with standard Rutherford Backscattering (RBS) and the resonant scattering on 16O at 3.045 MeV. Channeling angular scans are reproduced with Monte Carlo simulations. Irradiation induces a polygonization of the fluorite structure. Leaching leads to an incorporation of additional O atoms in the surface region of the UO 2 crystal which form a U 4O 9-like structure.

Orientation dependence of plastic deformation in NiAl single crystals

Compression stress-strain tests were performed on NiAl single crystals of various orientations at room temperature and complemented by observations of slip traces and dislocation structures. In ‘soft’ oriented samples (far from the [100] direction), 〈100〉 slip vectors are activated at a critical resolved shear stress of ≈90 MPa. The 〈100〉 slip is very homogeneous as witnessed by a faint and uniform slip line pattern. The yield stresses of soft orientations obey the Schmid law. For ‘hard’ orientations (within 3 ° from the [100] direction), the yield stress for 〈100〉 slip becomes too large and 〈111〉 slip is activated instead. The 〈111〉 slip is highly inhomogeneous and gives rise to distinct glide bands. The strain concentrated in these bands remains constant during deformation indicating that the plastic strain is carried by mobile dislocations at the periphery of the glide bands. We suppose that the difference in the slip homogeneity is due to highly different mobilities of 〈100〉 and 〈111〉 dislocations.

Anisotropy of transformation characteristics of Cu-base shape memory alloys

Shape memory alloy single crystals undergoing stress induced thermoelastic martensitic transformations exhibit strong anisotropy of deformation characteristics when loaded along various crystallographic axes. In the present work, CuAlNi and CuAlZnMn single crystals of various orientations were investigated by thermomechanical tension/compression tests. In particular, the orientation dependence of transformation strains and stress-temperature critical conditions for martensitic transformation were studied. Results have been summarized in stress-temperature phase diagrams which provide sufficient basis for micromechanical modeling of Cu-based polycrystals. Experimentally measured transformation strains were found to be in reasonable agreement with predictions based on the phenomenological theory of martensite crystallography.

Dislocation Slip Conditions and Structures in Copper Single Crystals Exhibiting Instabilities in Creep

Microstructural aspects of compressive creep at 723 to 773 K and its instabilities in copper single crystals of various orientations are investigated. Metallography, transmission electron microscopy, electron- and Laue X-ray diffraction were used to study dislocation slip. A computer simulation of a change of crystal orientation due to straining was applied to analyse dislocation slip conditions.

On the reproduction of ice from a common seed

This paper reports on the reproduction of ice sheets, achieved by serially growing them on a common seed from a melt of a desired composition. This was done with single crystals, polycrystalline columnar ice and mosaics composed of welded square-shaped crystals of various orientations. The use of welded crystal platelets as a seeding agent provides a means to study growth competition along boundaries of which all five degrees of freedom are defined at the onset of growth.

Cross-sectional TEM and corrosion studies of Al and N implanted copper

ABSTRACTPoly- and single crystalline copper was implanted with aluminium and nitrogen at doses ranging from 1016 to 5 × 1017 at/cm2 and energies of 170 keV. The corrosion resistance of the implanted surfaces was tested by exposure to an H25-containing atmosphere. The amount of copper sulphide formed was measured by chrono potentiometric reduction. The amount of corrosion products was markedly reduced (up to a factor 50) by high dose implantations of aluminium. The microstructure of the implanted copper was examined by Transmission Electron Microscopy of cross-sectioned specimens. A deep damage layer far exceeding the ion range was observed. XTEM-pictures of aluminium implanted copper single crystals of various orientations suggest a channeling mechanism for this deep damage layer. In situ annealing of the specimens in the TEM showed that most of the implantation damage is removed at 600°C except for an array of dislocations at the end of the damage range.

The tensile and fatigue deformation structures in a single crystal Ni-base superalloy

Dislocation structures produced in Rene N4 crystals of various orientations deformed in tension and low cycle fatigue (LCF) at 760 and 980 degrees C were examined in order to elucidate the observed differences in stress-strain behavior. Specimens tensile tested at 760 degrees C displayed significant crystallographic orientation dependences in mechanical response but comparable inhomogeneous dislocation structures. LCF specimens of various orientations had comparable cyclic stress-strain curves and generally similar somewhat more homogeneous dislocation structures. Tensile specimens at the higher temperature had comparable mechanical response and corresponding similar quite homogeneous dislocation structures with gamma' faulting; and LCF specimens had orientation-dependent mechanical response but comparable homogeneous loose dislocation networks.

Behavior of block boundaries during ultrasonic vibration in alkali halide crystals at temperatures 20?300�C

The behavior of block boundaries was investigated in alkali halide crystals of various orientations deformed by ultrasound at frequencies 40–73 kHz in the temperature interval 20–300°C. The specimen orientation was defined by the angle between the fourfold axis and the propagation direction of the ultrasonic wave. The initial stage of plastic deformation at room temperature is due to the generation of sources at the block boundaries in KCl and KBr, and by the heterogeneous nucleation of dislocation in NaCl and LiF. In the temperature interval 200–300°C, in NaCl and LiF dislocation multiplication begins already with the generation of sources at the block boundaries. In 30° orientation specimens the beginning of multiplication is preceded by the motion initiated by the ultrasound of sections of the block boundaries in the {1 0 0} secondary glide system.

Effect of irradiation on the deformation of copper and copper-aluminium alloys

The effect of low-temperature irradiation (<70°C) on the deformation of pure copper, Cu-0.09 wt% Al alloy, and Cu-0.19 wt% Al alloy was investigated. Tensile specimens were prepared from single crystals of various orientations, and were exposed to a neutron fluence of 6.85 ×1019 n/cm2(E>1 MeV) at a temperature less than 70°C. All irradiated and unirradiated specimens were pulled. A large increase in critical shear stress due to irradiation was observed; the increase was smaller in Cu-0.19 wt% Al alloy than in pure copper and Cu-0.09 wt% Al alloy. Ultimate shear stress and shear strain were less influenced by irradiation. Yield points were observed in all irradiated specimens. The yield drop was large in irradiated pure copper, and decreased with the increase of aluminium content in copper-aluminium alloys. All unirradiated specimens showed a high work-hardening coefficient (n) in the beginning of the deformation, followed by a lower value. By irradiation, the first value drastically decreased, while the second remained nearly constant. Shear stress and shear strain were influenced by crystal orientation.

Effect of growth rate on the dislocations structure of aluminium single crystals of various orientations

X-ray diffraction topography and the etch figure method were used to investigate the dislocation structure of single crystals of pure aluminium (99.999%) grown from the melt by the Bridgman method with 〈100〉, 〈111〉, 〈210〉 and 〈100〉 (near the pole) orientations of the solid-liquid interface with a growth rate range from 4 to 15 mm/min. It has been shown that the dependence of the dislocation density on the growth rate is determined by the crystallographic orientation of the solid-liquid interface. Thus, for crystals with 〈111〉 orientation the dependence of the dislocation density on the growth rate is weak, for crystals with 〈100〉 orientation it is very strong, while for crystals with 〈210〉 orientation this dependence is extremely large. The results obtained are explained on the basis of existing concepts about the anisotropy of mobility of the solid-liquid interface in the directions of preferred crystal growth.