Dislocation Substructure in NiAl Single Crystals Deformed at Ambient Temperature

1996 ◽  
Vol 460 ◽  
Author(s):  
X. Shi ◽  
T. M. Pollock ◽  
S. Mahajan ◽  
V. S. Arunachalam
Keyword(s):  
Ambient Temperature ◽  
Single Crystals ◽  
Dislocation Substructure ◽  
High Density ◽  
Weak Beam ◽  
Transmission Electron ◽  
Beam Transmission ◽  
Edge Dislocations ◽  
Double Cross

ABSTRACTDislocation substructure in NiAI single crystals oriented for single slip and deformed at ambient temperature has been studied using weak-beam transmission electron microscopy. Deformation is localized in bands that consists mostly of near-edge dislocations, with an interspersion of a high density of elongated prismatic loops. Pure screw dislocations are not observed, but dislocations having “zigzag” configurations that are near-screw in orientation are present. A high density of jogs is observed on both near-edge and zigzag dislocation segments. The mechanisms for the development of this substructure are discussed, emphasizing the role of double cross slip and resulting glissile and sessile jogs of varying heights.

Yield Stress Anomaly for 1/2〈112] {1111} Slip in y-Titanium Aluminide

1998 ◽  
Vol 552 ◽  
Author(s):  
S. Jiao ◽  
N. Bird ◽  
P. B. ◽  
G. Taylor
Keyword(s):  
Yield Stress ◽  
High Temperatures ◽  
Titanium Aluminide ◽  
Room Temperature ◽  
Elastic Strain Energy ◽  
Weak Beam ◽  
Transmission Electron ◽  
Different Temperatures ◽  
Edge Dislocations ◽  
Dislocation Dissociation

ABSTRACTTransmission electron microscopy (TEM) studies of dislocation structures in single crystals of TiAl containing 54.5 or 54.7 at% Al deformed at different temperatures revealed the occurrence of slip on ½〈112]{ {111} at room temperature and near the peak of the yield stress anomaly (YSA). Measurements of the corresponding yield stresses revealed the existence of a YSA for this type of slip. Weak-beam TEM showed the presence of locks at room temperature for 30° dislocations and at high temperatures for edge dislocations. Both types of locks involve dissociation on two intersecting { 1111} type planes, driven by reduction in elastic strain energy. The edge dislocation dissociation at high temperatures involves both climb and glide.

A Weak-Beam Study of the Microstructure of β-CUZN Deformed in the Domain of Flow Stress Anomaly

1988 ◽  
Vol 133 ◽  
Author(s):  
G. Dirras ◽  
P. Beauchamp ◽  
P. Veyssière
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Flow Stress ◽  
Single Crystals ◽  
Room Temperature ◽  
Burgers Vector ◽  
Weak Beam ◽  
Transmission Electron ◽  
Edge Component ◽  
Imaging Conditions

ABSTRACTβ-brass single crystals oriented along <001> were deformed between room temperature and 300°C. The deformation microstructure and dissociation properties were studied by transmission electron microscopy under weak-beam imaging conditions.Whatever the deformation temperature, superdislocations with <111> Burgers vector and strong edge component dominate within the microstructure. In addition, below the temperature of the flow stress peak (≈ 250°C), the density of screw relative to mixed superdislocations decreases as straining temperature increases. Dissociation does not always occur on the slip plane neither does it proceed exclusively by glide, even in samples deformed at 100°C.

Deformation Microstructures in B2-Type CoTi Single Crystals

1990 ◽  
Vol 213 ◽  
Author(s):  
M. Yoshida ◽  
T. Takasugi
Keyword(s):  
Yield Strength ◽  
Single Crystals ◽  
Compression Axis ◽  
Burgers Vector ◽  
Weak Beam ◽  
Transmission Electron ◽  
Beam Method ◽  
Orientation Axis ◽  
Means Of Transmission ◽  
Increasing Temperature

ABSTRACTB2-type CoTi single crystals which exhibit the yield strength anomaly were deformed at various temperatures and on various compression axis in order to investigate the deformation microstructures. The morphological feature and Burgers vectors of the activated dislocations were investigated by means of transmission electron microscopy. At a low temperature of 300 K, relatively straight dislocations with the <001>-type Burgers vector were observed. They consisted of the mixed components of edge and screw, and strongly tended to form the dipoles. At a temperature of 773 K where the yield stress increases with increasing temperature, the screw components of dislocations with a <001>-type Burgers vector were dominant and showed peculiar morphology revealing the pinning or cross slip. However, the examination using the weak-beam method could not show the evidence of any dissociation. At a high temperature of 973 K above the peak temperature, the Burgers vectors of activated dislocations were determined to be a <001>- type for compressive orientation axes close to [111] and [011] whereas a <110>-type for orientation axis close to [001]. These dislocation microstructures were discussed in correlation with the yield strength anomaly observed in these intermetallics.

scholarly journals The Role of the Multi Buffer Layer Technique on the Structural Quality of GaN

2000 ◽  
Vol 5 (S1) ◽  
pp. 398-404 ◽  
Author(s):  
M. Benamara ◽  
Z. Liliental-Weber ◽  
J.H. Mazur ◽  
W. Swider ◽  
J. Washburn ◽  
...  
Keyword(s):  
Dislocation Density ◽  
Buffer Layers ◽  
Structural Quality ◽  
Transmission Electron ◽  
Layer Technique ◽  
Growth Method ◽  
Microscopy Techniques ◽  
Edge Dislocations

Successive growth of thick GaN layers separated by either LT-GaN or LT-AlN interlayers have been investigated by transmission electron microscopy techniques. One of the objectives of this growth method was to improve the quality of GaN layers by reducing the dislocation density at the intermediate buffer layers that act as barriers to dislocation propagation. While the use of LT-AlN results in the multiplication of dislocations in the subsequent GaN layers, the LT-GaN reduces dislocation density. Based upon Burgers vector analysis, the efficiency of the buffer layers for the propagation of the different type of dislocations is presented. LT-AlN layer favor the generation of edge dislocations, leading to a highly defective GaN layer. On the other hand, the use of LT-GaN as intermediate buffer layers appears as a promising method to obtain high quality GaN layer.

Dislocation substructure in NiAl single crystals cyclically deformed at ambient temperature

1994 ◽  
Vol 42 (11) ◽  
pp. 3731-3740 ◽  
Author(s):  
C.G. Kallingal ◽  
T.R. Smith ◽  
N.S. Stoloff ◽  
K. Rajan
Keyword(s):  
Ambient Temperature ◽  
Single Crystals ◽  
Dislocation Substructure

scholarly journals High-Density Well-Aligned Dislocations Introduced by Plastic Deformation in Bi1−xSbx Topological Insulator Single Crystals

Crystals ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 317 ◽  
Author(s):  
Yuki Tokumoto ◽  
Riku Fujiwara ◽  
Keiichi Edagawa
Keyword(s):  
Single Crystals ◽  
Surface States ◽  
Zone Melting ◽  
High Density ◽  
Experimental Investigations ◽  
Dirac Fermions ◽  
Fundamental Study ◽  
Transmission Electron ◽  
Spin Polarized ◽  
Device Applications

Topological insulators (TIs) have a bulk bandgap and gapless edge or surface states that host helically spin-polarized Dirac fermions. Theoretically, it has been predicted that gapless states could also be formed along dislocations in TIs. Recently, conductivity measurements on plastically deformed bismuth antimony (Bi1−xSbx) TIs have revealed excess conductivity owing to dislocation conduction. For further application of them, fundamental study on dislocations in TIs is indispensable. Dislocations controlled based on fundamental studies could potentially be useful not only for experimental investigations of the dislocation properties but also for diverse device applications. In the present study, Bi1−xSbx TI single crystals were fabricated by a zone-melting method. The crystals were plastically deformed at room temperature. The resultant dislocations were observed by transmission electron microscopy (TEM). It was found that high-density dislocations with the Burgers vector satisfying the condition for the formation of gapless states were successfully introduced. The dislocations were mostly of edge type with lengths on the order of more than a few micrometers.

Analysis of Weak-Beam Contrast from SESF/SISF Fault Pairs Associated with ½ <112] Superdislocations in TiAl

1998 ◽  
Vol 552 ◽  
Author(s):  
Mukul Kumar ◽  
S. Sriram ◽  
Adam J. Schwartz ◽  
Vijay K. Vasudevan
Keyword(s):  
Stacking Faults ◽  
Antiphase Boundary ◽  
Stacking Fault ◽  
Intermetallic Alloy ◽  
Diffraction Contrast ◽  
Weak Beam ◽  
Partial Dislocations ◽  
Transmission Electron ◽  
Beam Transmission ◽  
Simulated Images

ABSTRACTThe diffraction contrast from dissociated ½<112] superdislocations in γ-TiAl intermetallic alloy cannot always be analyzed using conventional rules of diffraction contrast. In particular, the configuration involving three similar Shockley partials on adjacent planes has often been ruled out due to the absence of fringes indicating the presence of stacking faults. In order to determine the dissociated configuration, weak-beam transmission electron microscope observations of edge-oriented ½<112] superdislocations have been correlated with computer simulated images. Dissociation of these superdislocations into three similar ⅙<112] partial dislocations bounding a superlattice extrinsic and intrinsic stacking fault pair has been consequently determined from these analyses. It has been found that diffraction contrast alone cannot distinguish between the various configurations that lead to the formation of the fault pair, but the formation of an antiphase boundary or complex stacking fault linked dissociation or locking by stair rod dislocations can be ruled out.

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