scholarly journals Субструктура интерметаллического соединения Cu-=SUB=-3-=/SUB=-Sn в тонкопленочном состоянии

2019 ◽  
Vol 89 (6) ◽  
pp. 907
Author(s):  
А.Н. Макрушина ◽  
В.А. Плотников ◽  
Б.Ф. Демьянов ◽  
С.В. Макаров
Keyword(s):  
Slip System ◽  
Interplanar Distance ◽  
Dislocation Motion ◽  
Thin Layers ◽  
Long Period ◽  
Partial Dislocations ◽  
Pyramidal Slip ◽  
Narrow Homogeneity Range ◽  
Slip Traces ◽  
Uniform Extension

AbstractThe crystalline structure of intermetallic Cu_3Sn synthesized by successively condensing thin layers of copper and tin on a substrate at 150°C has been studied. Cu_3Sn compound exists in a very narrow homogeneity range and has a long-period close-packed ordered D0_19 superstructure. It has been found that the crystal lattice exhibits many slip traces associated with dislocation motion. The dislocation motion is due to the stressed state of the crystal, which can be characterized as uniform extension. Electron micrographs show that slip traces in the Cu_3Sn crystal are parallel to the ( $$\bar {1}\bar {1}21$$ ) and ( $$11\bar {2}1$$ ) planes belonging to pyramidal slip system II, which is a main slip system along with pyramidal and basal ones. Slip traces result from the motion of partial dislocations, as indicated by the amount of slip, which is equal to half the interplanar distance. Since the crystal is ordered, slip is accomplished by a pair of superpartial dislocations and a slip trace may be a superstructural or complex stacking fault.

scholarly journals Multi-strengthening-mechanisms in a novel titanium alloy with (TiHf)5Si3 particle-reinforcement

2020 ◽  
Vol 321 ◽  
pp. 11078
Author(s):  
Yan Du ◽  
Jinwen Lu ◽  
Wei Zhang ◽  
Yusheng Zhang
Keyword(s):  
Dislocation Motion ◽  
Heat Treatments ◽  
Triple Junctions ◽  
Strengthening Mechanisms ◽  
Particle Reinforcement ◽  
Solid Solution Strengthening ◽  
Long Period ◽  
Solution Strengthening ◽  
Dislocation Strengthening ◽  
Particle Strengthening

The microstructure and mechanical properties of Ti-2Si-2Nb-2Fe-1Hf-1Ta-1W alloy with (TiHf)5Si3 particle-reinforcement and their underlying relations have been studied. Electron microscope observations and correlative statistical analysis have been made to analyze microstructure evolution with heat treatments. The (TiHf)5Si3 particles with 800 nm in diameter were found uniformly distributed at α/β boundaries and triple junctions and turned out to be stable even after heat treatments at high temperature for a long period, inhibiting grain growth and dislocation motion. In addition, multi-strengthening-mechanisms including particle strengthening, solid-solution strengthening, grain boundary strengthening and dislocation strengthening have been discussed.

Threading Dislocation Density Reduction in GaN/Sapphire Heterostructures.

1999 ◽  
Vol 595 ◽  
Author(s):  
A. Kvit ◽  
A. K. Sharma ◽  
J. Narayan
Keyword(s):  
Basal Plane ◽  
Stacking Faults ◽  
High Density ◽  
Thin Layers ◽  
Interfacial Region ◽  
Threading Dislocation ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Plan View ◽  
Partial Dislocations

AbstractLarge lattice mismatch between GaN and α-Al2O3 (15%) leads to the possibility of high threading dislocation densities in the nitride layers grown on sapphire. This investigation focused on defect reduction in GaN epitaxial thin layer was investigated as a function of processing variables. The microstructure changes from threading dislocations normal to the basal plane to stacking faults in the basal plane. The plan-view TEM and the corresponding selected-area diffraction patterns show that the film is single crystal and is aligned with a fixed epitaxial orientation to the substrate. The epitaxial relationship was found to be (0001)GaN∥(0001)Sap and [01-10]GaN∥[-12-10]Sap. This is equivalent to a 30° rotation in the basal (0001) plane. The film is found to contain a high density of stacking faults with average spacing 15 nm terminated by partial dislocations. The density of partial dislocations was estimated from plan-view TEM image to be 7×109 cm−2. The cross-section image of GaN film shows the density of stacking faults is highest in the vicinity of the interface and decreases markedly near the top of the layer. Inverted domain boundaries, which are almost perpendicular to the film surface, are also visible. The concentration of threading dislocation is relatively low (∼;2×108 cm−2), compared to misfit dislocations. The average distance between misfit dislocations was found to be 22 Å. Contrast modulations due to the strain near misfit dislocations are seen in high-resolution cross-sectional TCM micrograph of GaN/α-Al2O3 interface. This interface is sharp and does not contain any transitional layer. The interfacial region has a high density of Shockley and Frank partial dislocations. Mechanism of accommodation of tensile, sequence and tilt disorder through partial dislocation generation is discussed. In order to achieve low concentration of threading dislocations we need to establish favorable conditions for some stacking disorder in thin layers above the film-substrate interface region.

Mg-Zn-Y Alloys with Long-Period Stacking Ordered Phases: Deformation, Creep, Solute Segregation and Strengthening Mechanisms at Elevated Temperatures

2016 ◽  
Vol 879 ◽  
pp. 2204-2209 ◽  
Author(s):  
Zhi Qing Yang ◽  
Wei Wei Hu ◽  
Heng Qiang Ye
Keyword(s):  
Plastic Deformation ◽  
Creep Resistance ◽  
Basal Slip ◽  
Elevated Temperatures ◽  
Stacking Faults ◽  
Dislocation Motion ◽  
Tensile Creep ◽  
Lpso Phase ◽  
Long Period ◽  
Cottrell Atmospheres

Mg-Zn-Y alloys with long-period stacking ordered (LPSO) phases have superior strength at elevated temperatures. We studied plastic deformation and creep behavior of a Mg97Zn1Y2 (at.%) alloy. Deformation kinking of the LPSO phase plays an important role in strengthening the alloy during compression at elevated temperatures. Growth stacking faults with Zn/Y segregation can act as obstacles to non-basal slip and deformation twinning in Mg matrix. The tensile creep strain was only about 0.01% under a tensile stress of 70MPa for 100h at 200 °C, demonstrating excellent creep resistance of this alloy. Generation and motion of basal dislocations led to bending of LPSO phase during tensile creep of the Mg97Zn1Y2 (at.%) alloy. Plastic deformation in Mg grains was mostly achieved through basal slip during creep at temperatures below 200 °C, while non-basal slip through the generation and motion of “a + c” dislocations was activated with increasing the temperature to 200 °C and above. Dissociation of dislocations and Suzuki segregation on basal planes occurred widely in Mg matrix, which hindered dislocation motion and thus played an important role in preventing Mg grains from softening during deformation at elevated temperatures. In addition, Cottrell atmospheres were observed along dislocations in plastically deformed LPSO phase, impeding motion of dislocations. The superior strength and creep resistance of the Mg97Zn1Y2 (at.%) alloy at elevated temperatures are thus associated with the LPSO phase, stacking faults in Mg grains, formation of Cottrell atmospheres in LPSO and occurrence of Suzuki segregation in Mg.

Observation of dislocation reactions in CDTE at lattice resolution

1983 ◽  
Vol 41 ◽  
pp. 112-113
Author(s):  
T. Yamashita ◽  
R. Sinclair
Keyword(s):  
Partial Dislocation ◽  
Video Recording ◽  
Dislocation Motion ◽  
Video Tape ◽  
Exposure Rate ◽  
Shockley Partial Dislocation ◽  
Shockley Partial ◽  
Partial Dislocations ◽  
Lattice Resolution ◽  
Obvious Extension

Recently, lattice resolution video-recording of dislocation motion in CdTe has been reported by Sinclair et al, using the Cambridge 500 keV microscope equipped with a TV camera. Phenomena such as the motion of Shockley partial dislocations and climb of Frank dislocations were recorded onto a video tape which has an exposure rate of 50 half-frames per second. An obvious extension of this work is to study the dislocation reactions. An example of such a reaction which was detected in CdTe is shown in Fig. 1. The micrographs were taken several seconds apart in a JEOL 200CX microscope, and they show dissociation of a Frank dislocation into a Shockley partial dislocation and a Lomer dislocation (ie., a sessile lock).

Tensile Deformation Behavior of Magnesium Single Crystals with Different Yttrium Concentrations

2021 ◽  
Vol 1016 ◽  
pp. 516-521
Author(s):  
Tomohiro Hanada ◽  
Masayuki Tsushida ◽  
Hiromoto Kitahara ◽  
Shinji Ando
Keyword(s):  
Slip System ◽  
Single Crystals ◽  
Yield Stress ◽  
Tensile Deformation ◽  
Tensile Tests ◽  
Second Order ◽  
Pyramidal Slip ◽  
Tensile Deformation Behavior ◽  
Yttrium Addition ◽  
Critical Resolved Shear Stress

Tensile tests of Mg-Y single crystals with different yttrium concentrations: 0.07 and 0.3 at.% were carried out to investigate effects of yttrium on pyramidal <c+a> slip system. In Mg-0.07at%Y alloy single crystals, {11 2}< 23> second order pyramidal <c+a> slip was activated and yield stress increased, compared to pure Mg single crystals. On other hand, in Mg-0.3at%Y alloy single crystals, {10 1}< 23> first order pyramidal <c+a> slip was activated and yield stress increased, compared to Mg-0.07at%Y alloy single crystals. The change in slip system by yttrium addition would be caused by increasing critical resolved shear stress (CRSS) for second order pyramidal slip.

Densification Behavior in Spark-Plasma-Sintering of MgAl2O4 Spinel

2010 ◽  
Vol 654-656 ◽  
pp. 1986-1989
Author(s):  
Koji Morita ◽  
Byung Nam Kim ◽  
Hidehiro Yoshida ◽  
Keijiro Hiraga
Keyword(s):  
Effective Stress ◽  
Partial Dislocation ◽  
Stacking Faults ◽  
Dislocation Motion ◽  
Densification Rate ◽  
Densification Mechanism ◽  
Partial Dislocations ◽  
Plasma Sintering ◽  
Rate Relationship ◽  
Spark Plasma

The densification mechanism in park-plasma-sintering (SPS) processing was examined in MgAl2O4 spinel. As the relative density ρt increases, that is, as the effective stress σeff decreases, stress exponent n evaluated from effective stress-densification rate relationship continuously varies from n  4 to n  1. TEM observation shows that significant stacking faults caused by partial dislocations are frequently observed in the low ρt region. The results suggest that, for spinel, the predominant densification mechanism in SPS processing changes with ρt from plastic flow by a partial dislocation motion in the low ρt region (n  4) to diffusion-related creep in the high ρt region (n  1).

Slip trace characterisation of Ni3Al by atomic force microscopy.

2000 ◽  
Vol 646 ◽  
Author(s):  
Christophe Coupeau ◽  
Tomas Kruml ◽  
Joël Bonneville
Keyword(s):  
Atomic Force Microscopy ◽  
Flow Stress ◽  
Plastic Strain ◽  
Slip System ◽  
Mean Free Path ◽  
Force Microscopy ◽  
Atomic Force ◽  
Slip Traces ◽  
Octahedral Slip ◽  
Increasing Temperature

ABSTRACTWe examined by atomic force microscope the slip traces produced on Ni3Al single crystals pre-deformed up to nearly 1% plastic strain at three temperatures in the anomaly domain: 293K, 500K and 720K. It is observed that, whatever the deformation temperature, the slip traces essentially belong to the primary octahedral slip system. The lengths of the slip lines become shorter and shorter with increasing temperature, while the number of dislocations that constitutes the lines is approximately constant. These results are interpreted in terms of a decreasing mean free path of the mobile dislocations when the temperature is raised. The implications of these results in the understanding of the flow stress anomaly are underscored.

Deformation and Dislocation Structure of Ti3AI Single Crystals

1990 ◽  
Vol 186 ◽  
Author(s):  
Y. Minonishi
Keyword(s):  
Slip System ◽  
Single Crystals ◽  
Yield Stress ◽  
Dislocation Structure ◽  
Deformation Characteristics ◽  
Prism Slip ◽  
Pyramidal Slip ◽  
Pure Metals

AbstractDeformation characteristics of Ti3A1 single crystals has been examined as a function of orientation and temperature. This paper mainly describes the result of compression along the c axis. In this orientation, the yield stress increases from 300 to 1100K, decreasing rapidly thereafter. The slip system activated are {1121}<1126> and dislocations observed are nearly of edge character. The anomaly is discussed in comparison with the behavior of other intermetallics and pure metals. An important role this pyramidal slip plays in polycrystalline ductility of Ti3Al is shown in the light of the briefly described results of the prism slip.

scholarly journals Long-period unstable gravity-waves and associated VHF radar echoes

1997 ◽  
Vol 15 (6) ◽  
pp. 813-822 ◽  
Author(s):  
R. M. Worthington ◽  
L. Thomas
Keyword(s):  
Gravity Waves ◽  
Wind Shear ◽  
Thin Layers ◽  
Symmetric Pair ◽  
Strong Wind ◽  
Jet Streams ◽  
Vhf Radar ◽  
Mountain Waves ◽  
Long Period ◽  
Wind Shears

Abstract. VHF atmospheric radar is used to measure the wind velocity and radar echo power related to long-period wind perturbations, including gravity waves, which are observed commonly in the lower stratosphere and tropopause region, and sometimes in the troposphere. These wind structures have been identified previously as either inertia-gravity waves, often associated with jet streams, or mountain waves. At heights of peak wind shear, imbalances are found between the echo powers of a symmetric pair of radar beams, which are expected to be equal. The largest of these power differences are found for conditions of simultaneous high wind shear and high aspect sensitivity. It is suggested that the effect might arise from tilted specular reflectors or anisotropic turbulent scatterers, a result of, for example, Kelvin-Helmholtz instabilities generated by the strong wind shears. This radar power-difference effect could offer information about the onset of saturation in long-period waves, and the formation of thin layers of turbulence.

Influence of Grain Boundary on Activation of Slip Systems in Magnesium: Crystal Plasticity Analysis

2010 ◽  
Vol 654-656 ◽  
pp. 695-698 ◽  
Author(s):  
Tsuyoshi Mayama ◽  
Tetsuya Ohashi ◽  
Kenji Higashida
Keyword(s):  
Grain Boundary ◽  
Slip System ◽  
Crystal Plasticity ◽  
Crystal Orientation ◽  
Basal Slip ◽  
Prismatic Slip ◽  
Shear Stresses ◽  
Slip Systems ◽  
Analysis Method ◽  
Pyramidal Slip

Crystal plasticity finite element analysis method considering the accumulation of geometrically necessary (GN) dislocations was applied to monotonic loading of pure magnesium bi-crystal. The deformation mechanisms considering in the present analysis method are basal slip <a>, prismatic slip <a>, 1st order pyramidal slip <a>, 2nd order pyramidal slip <a+c> and tensile twinning <a+c>. Tensile twinning is incorporated into crystal plasticity analysis assuming that twinning plane and direction of shear by twinning are equivalent to slip plane and slip direction, respectively. Critical resolved shear stresses (CRSSs) for each slip system in the literatures were used. Analysis model is designed to investigate the influence of grain boundary on the activation of slip systems. That is, one grain consisting of bi-crystal (grain A) had the crystal orientation whose Schmid factor for prismatic slip is 0.5. The crystal orientation of the other grain (grain B) was slightly deviated from that of grain A. The result of the calculation of tensile loading of the bi-crystal showed that both grains are deformed by the multiple slip of basal slip system, which resulted in the formation of GN dislocation bands.

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