Dislocation Structure in Single Crystal L1o Type Ti-Al-V Compound

1990 ◽  
Vol 213 ◽  
Author(s):  
Y.D. Hahn ◽  
Z.X. Li ◽  
S.H. Whang ◽  
T. Kawabata
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
High Temperatures ◽  
Dislocation Structure ◽  
The Other ◽  
Dislocation Loops ◽  
Single Slip ◽  
Pile Up ◽  
Favorable Configuration ◽  
Dipole Form

ABSTRACTSingle Crystals of L1o type Ti44Al54V2 alloy were deformed at high temperatures and various orientations. The dislocations thus produced by single slip were studied by TEM. 1/2<110] dislocations produced at 1073 K consist of dislocation loops and curled dislocations with spiral segments, which is in agreement with those shown in the polycrystalline Ti-Al-V, and -Nb alloys deformed under the same conditions. The normal dislocations produced at 873 K pile up in groups, each of which contains several straight dislocations with a screw character. On the other hand, the majority of superdislocations produced at 873 K were found in a dipole form, indicating that the dipole is a favorable configuration at this temperature.

Orientation Dependent Strength and Cross-Slip Structure of Ordinary Dislocations in Single Crystal γ-Ti-56A1

1998 ◽  
Vol 552 ◽  
Author(s):  
Q. Feng ◽  
S. H.
Keyword(s):  
Single Crystal ◽  
High Temperatures ◽  
Slip Plane ◽  
Forward Direction ◽  
Orientation Dependence ◽  
Cross Slip ◽  
Dislocation Loops ◽  
Single Slip ◽  
Anomalous Hardening ◽  
Double Cross

ABSTRACTThe temperature as well as orientation dependence in anomalous hardening occurs in single crystal Ti-56AI between 673K and 1073K under single slip of ordinary dislocations. The ordinary dislocations (1/2<110]) are gliding not only on (111) plane but also on (110) plane in the temperature range where the anomalous hardening occurs in single crystal Ti-56A1. The TEM study shows that the (110) cross-slip of ordinary dislocations is a double cross-slip in nature in which first, the dislocations cross-slip from the primary (111) slip plane to (110) plane followed by cross-slipping again onto another primary slip plane. This double cross-slip leaves a pair of edge segments 'superjogs' in (110) planes. It appears that these superjogs are immobile in the forward direction and act as pinning points. Furthermore, these pinning points would act as a Frank-Read source for the double cross-slipped dislocations, which generate dislocation loops as well as dislocation dipoles. The pinning structure, multiplane dislocation loops, and dipoles of double cross-slip origin all contribute to anomalous hardening at high temperatures in this material.

The detection of submicroscopic lattice defects in aluminium utilizing a vacancy supersaturation

1969 ◽  
Vol 314 (1516) ◽  
pp. 129-141 ◽  
Keyword(s):  
Single Crystals ◽  
Screw Dislocation ◽  
Lattice Defects ◽  
Supersaturated Solution ◽  
Dislocation Loops ◽  
Single Slip ◽  
Quench Temperature ◽  
Decoration Technique

The conditions under which submicroscopic defects can be revealed due to decoration by the precipitation of vacant lattice sites from a supersaturated solution have been investigated in aluminium. It is shown that quench temperature, specimen purity and other conditions have to be so chosen that the nucleation of self-sinks is minimized while an adequate vacancy supersaturation is maintained. The conditions for the optimum visibility of defects revealed in this way have been studied primarily by observing the variation in the density of rows of dislocation loops along <110> directions. This decoration technique has been used in quenched single crystals deformed in single slip to show that these rows and also narrow faulted dislocation dipoles with their long axes in the <110> direction form along the specific <110> direction predicted from a hypothesis involving the dragging of a jog by a moving screw dislocation.

Successive Magnetic Transitions on Single Crystal Cu3(OH)4SO4

2011 ◽  
Vol 170 ◽  
pp. 194-197
Author(s):  
Shigeo Hara ◽  
Hirohiko Sato
Keyword(s):  
Magnetic Field ◽  
Single Crystal ◽  
Single Crystals ◽  
Field Dependence ◽  
Easy Axis ◽  
The Other ◽  
Magnetic Transitions ◽  
Copper Hydroxide ◽  
High Quality ◽  
Measured Field

Cu3(OH)4SO4, a parallel Cu (S = 1/2) triple chain system, is an interesting magnet because an idle-spin state is expected on the central chain. We have succeeded in growing high-quality single crystals of Cu3SO4(OH)4 by a hydrothermal method from copper sulfate and copper hydroxide. We measured field dependence of the magnetization on a single crystal under various directions of magnetic field up to 7 T. We found a clear magnetic anisotropy and confirmed that the existence of the easy axis lies in the ac plane. Under magnetic fields parallel to the c-axis and the a-axis at 2.5 K, we observed field-induced successive magnetic transitions. In the case of B//c, two anomalies of the magnetization are observed at 0.9 and 1.7 T, On the other hand, there are broad anomalies in the magnetization at 3.7 and 5.6 T in the case of B//a.

scholarly journals Success or Failure of Chiral Crystallization of Similar Heterocyclic Compounds

Molecules ◽  
2020 ◽  
Vol 25 (23) ◽  
pp. 5691
Author(s):  
Cyprian M. Chunkang ◽  
Iris E. Ikome ◽  
Emmanuel N. Nfor ◽  
Yuta Mitani ◽  
Natsuki Katsuumi ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Single Crystal ◽  
Single Crystals ◽  
Heterocyclic Compounds ◽  
Van Der Waals ◽  
Van Der Waals Forces ◽  
The Other ◽  
X Ray ◽  
Other Hand

Single crystals of two achiral and planar heterocyclic compounds, C9H8H3O(CA1) and C8H5NO2 (CA4), recrystallized from ethanol, were characterized by single crystal X-ray analysis, respectively, and chiral crystallization was observed only for CA1 as P212121 (# 19), whereas it was not observed for CA4 P21/c (# 14). In CA1, as a monohydrate, the hydrogen bonds were pronounced around the water of crystallization (O4), and the planar cyclic sites were arranged in parallel to slightly tilted positions. On the other hand, an anhydride CA4 formed a dimer by hydrogen bonds between adjacent molecules in the crystal, which were aggregated by van der Waals forces and placed in parallel planar cyclic sites.

Darstellung und Strukturbeschreibung von NaCa3 Mn(V2O7)(V3O10) / Preparation and Structure of NaCa3Mn(V2O7)(V3O10)

1998 ◽  
Vol 53 (5-6) ◽  
pp. 507-511 ◽  
Author(s):  
R. Rettich ◽  
Hk. Müller-Buschbaum
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Argon Atmosphere ◽  
Statistical Distribution ◽  
The Other ◽  
Space Group ◽  
X Ray ◽  
Point Position ◽  
Symmetry Space ◽  
Symmetry Space Group

Abstract Single crystals of NaCa3 Mn(V2O7)(V3O10) have been prepared by crystallization from flux in argon atmosphere. X-Ray single crystal methods led to triclinic symmetry, space group C1i - P 1̄, a = 6.8798(9), b = 6.902(1), c = 15.480(2) Å, α = 87.39(1), β = 85.32(1), γ = 86.25(2) °, Z = 2. The compound belongs to the rare trivanadates showing V2O7 and V3O10 groups incorporated into a NaCaMn/O framework. One point position of the cations is occupied by Ca2+, three by Na+ and Ca2+ in a statistical distribution and a fourth one by Mn2+. The surrounding of Mn2+ and the statistically occupied position M(3) are octahedra, the other metal positions are centers of capped trigonal prisms.

Effect of Antiphase Domain Boundaries on Prism Slip in Ti3Al Single Crystals

2002 ◽  
Vol 753 ◽  
Author(s):  
Y. Koizumi ◽  
Y. Minamino ◽  
N. Tsuji ◽  
T. Nakano ◽  
Y. Umakoshi
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Yield Stress ◽  
Dislocation Structure ◽  
Antiphase Domain ◽  
Prism Slip ◽  
Domain Boundaries ◽  
Antiphase Domains

ABSTRACTEffect of antiphase domain boundaries (APDBs) on yielding and dislocation structure were investigated in Ti3Al single crystals oriented for prism slip. The yield stress greatly depended on the size of antiphase domains (APDs). The yield stress of Ti3Al with the average APD size of 35nm was about six times higher than that of Ti3Al without APDB. Single dislocations (isolated superpartial dislocations) were observed in the deformed Ti3Al single crystal with APD sizes smaller than 100nm, while superdislocation pairs were observed in those with larger APDs. The mechanism of the interaction between the prism dislocations and APDBs is discussed.

Dislocation Structure Evolution in Thin Single Crystal Plates Under Cyclic Loading

1995 ◽  
Vol 399 ◽  
Author(s):  
Yury. N. Stepanov ◽  
Alexander M. Scorupsky
Keyword(s):  
Material Processing ◽  
Cyclic Loading ◽  
Single Crystal ◽  
Dislocation Structure ◽  
Material Properties ◽  
Uniaxial Loading ◽  
Structure Evolution ◽  
Dislocation Loops ◽  
Optimum Regime

ABSTRACTThe effect of cyclic uniaxial loading applied to surfaces of thin single crystal plates on dislocation structure is analyzed analytically and numerically. This work investigates detailed changes in dislocation structure near surfaces and in size and concentration of dislocation loops inside the crystal. The results may be helpful in choosing the optimum regime for material processing and in predicting material properties.

Dislocation loops in single-crystal NiAl

1990 ◽  
Vol 48 (4) ◽  
pp. 942-943
Author(s):  
Yaping Liu
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Single Crystals ◽  
Cyclic Deformation ◽  
Tensile Strain ◽  
Tensile Deformation ◽  
Dislocation Loops ◽  
Image Position ◽  
Edge Dislocations

In the conventional viewpoint, dislocation loops of vacancy type in single crystal NiAl can only exist in Al-rich compositions. Their configurations and their changes when deformation occurs, and their effects on the deformation have not been studied thoroughly.In the present study, nickel-rich NiAl single crystals of 48.1∼48.6 at %A1 were annealed at 1315°C for 50 hours, then cooled at 200°C/hr to permit vacancy condensation. Single-crystal samples cut with an [001] axis then underwent high temperature (850°C) tensile and cyclic deformation. TEM specimens were cut from the undeformed, 0.3% tensile strain, ±0.5 cyclic and 30∼40% tensile deformation samples.Two kinds of dislocations, edge and screw, were found in the undeformed NiAl. Edge dislocations consisted of concentric dislocation loops (Fig. 1) and spiral dislocations (dislocation A in Fig. 2). They lie on cubic planes and have cubic line orientations. Invisibility conditions of g.b=0 and g.b x u=0 show that they have <001> type Burgers vectors normal to the loop planes. The shift in image position on changing the sign of g was used to verify that the loops are vacancy in nature.

Oxidation Behaviours of MoSi2 Single Crystal at the Temperatures of 773K and 1473K

2007 ◽  
Vol 561-565 ◽  
pp. 453-457
Author(s):  
Lan Ting Zhang ◽  
Ai Dang Shan ◽  
Jian Sheng Wu
Keyword(s):  
High Temperature ◽  
Single Crystal ◽  
Single Crystals ◽  
Oxidation Resistance ◽  
Oxidation Kinetics ◽  
Oxidation Behaviour ◽  
The Other ◽  
Columnar Growth ◽  
Good Oxidation Resistance ◽  
Parabolic Law

MoSi2 is a potential high temperature structural materials and shows excellent oxidation resistance at high temperatures. To explore its oxidation behaviour and mechanism, MoSi2 single crystals were prepared and investigated in the present work. The experimental results showed that different from its polycrystalline, MoSi2 single crystal showed good oxidation resistance at both 773 and 1473K. Near parabolic law of oxidation kinetics was followed for all the investigated surfaces of MoSi2 single crystal. The close-packed (110) surface of MoSi2 single crystal showed the best oxidation resistance at both temperatures. After exposure at 773K, the molybdenum oxide formed on the (110) surface of MoSi2 single crystal was found to be Mo4O11 instead of MoO3 formed on the other surfaces. Morphology observation showed a columnar growth of Mo4O11 on the (110) surface. No difference was found on the oxide formed for different surfaces of MoSi2 single crystal at 1473K.

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