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.

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.

Slip Transition and Dislocation Structures in Off-Stoichiometric NiAl Single Crystals

1996 ◽  
Vol 460 ◽  
Author(s):  
R. Srinivasan ◽  
M. F. Savage ◽  
M. S. Daw ◽  
R. D. Noebe ◽  
M. J. Mills
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Yield Strength ◽  
Single Crystals ◽  
Compression Tests ◽  
Transmission Electron ◽  
Strength Curve ◽  
Slip Transition

ABSTRACTCompression tests have been performed on hard-oriented Ni-44A1 single crystals for several temperatures and strain levels. There is a slip transition from a<111> type slip to non-a<111> type slip which corresponds with the observation of yield points. Transmission electron microscopy studies provide evidence for decomposition of a<111> dislocations into a<101> and a<010> dislocations near the “knee” of the yield strength curve. The mechanism of this slip transition and the nature of the dislocation processes both below and above the “knee” are described.

Plasticity of decagonal Al73Ni10Co17 quasicrystals

2003 ◽  
Vol 805 ◽  
Author(s):  
Peter Schall ◽  
Michael Feuerbacher ◽  
Knut Urban
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Plastic Deformation ◽  
Deformation Mechanisms ◽  
Compression Tests ◽  
Compression Axis ◽  
Decagonal Quasicrystal ◽  
Transmission Electron ◽  
Axis Parallel ◽  
Means Of Transmission

ABSTRACTWe present a study of the deformation mechanism of decagonal Al73Ni10Co17 quasicrystals by means of transmission electron microscopy. We performed compression tests on single-quasicrystalline samples in three different orientations: with the compression axis parallel to, inclined by 45 ° and perpendicular to the tenfold axis of the decagonal quasicrystal. The deformed samples reveal characteristic orientation-dependent dislocation structures leading us to the conclusion that fundamentally different deformation mechanisms are involved in plastic deformation in the three deformation geometries. We explicitly identified the Burgers vectors of the dislocations as interatomic vectors in the structure of decagonal Al-Ni-Co.

On the Effect of Strain Rate and Temperature on the Yield Strength Anomaly in L21-structured Fe2AlMn

2008 ◽  
Vol 1128 ◽  
Author(s):  
Markus W. Wittmann ◽  
Janelle M. Chang ◽  
Yifeng Liao ◽  
Ian Baker
Keyword(s):  
Yield Strength ◽  
Strain Rate ◽  
Single Crystals ◽  
Yield Stress ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Temperature Range ◽  
Effects Of Temperature ◽  
Increasing Temperature

AbstractThe effects of strain rate and temperature on the yield strength of near-stoichiometric Fe2AlMn single crystals were investigated. In the temperature range 600-800K the yield stress increased with increasing temperature, a response commonly referred to as a yield strength anomaly. No strain rate sensitivity was observed below 750K, but at higher temperatures the yield stress increased with increasing strain rate. Possible mechanisms to explaining the effects of temperature and strain rate are discussed.

TEM study of dislocation core configurations in Ni3(Al,l%Ta) deformed at high temperatures

1990 ◽  
Vol 48 (4) ◽  
pp. 474-475
Author(s):  
N. Baluc
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Yield Strength ◽  
Constant Strain Rate ◽  
Dislocation Core ◽  
Anomalous Increase ◽  
Weak Beam ◽  
Transmission Electron ◽  
Ordered Alloys ◽  
High Resolution Tem

The Ni3Al intermetallic compound of the ordered L12 structure with various alloying elements (such as Ta or Ti) reinforces most of the industrial superalloys which are designed for high temperature applications. Therefore, the understanding of its mechanical properties is of primary importance. The yield strength, measured in constant strain rate tests, exhibits an anomalous behaviour as a function of temperature: it increases up to a peak temperature above which it finally decreases. The anomalous increase has been extensively studied during the last 30 years, including weak-beam and high resolution transmission electron microscopy (TEM) observations and computer simulations. Numerous models have been proposed to explain this anomalous variation in which the structure of the dislocation core plays a fundamental role. A review of core effects on the plasticity of ordered alloys was given by Vitek (1985). In the present investigation, the Ni3(Al,l%Ta) phase was deformed at temperatures above the yield strength peak and the detailed core configurations of dislocations have been analyzed using weak-beam and high resolution TEM techniques.

Deformation-Induced Dislocations in 4H-SiC and GaN

1999 ◽  
Vol 572 ◽  
Author(s):  
M. H. Hong ◽  
A. V. Samant ◽  
V. Orlov ◽  
B. Farber ◽  
C. Kisielowski ◽  
...  
Keyword(s):  
Deformation Temperature ◽  
Stacking Fault ◽  
Dense Array ◽  
Prism Plane ◽  
Burgers Vector ◽  
Temperature Range ◽  
Weak Beam ◽  
Beam Method ◽  
Bulk Single Crystals ◽  
Gan Film

ABSTRACTBulk single crystals of 4H-SiC have been deformed in compression in the temperature range 550–1300°C, whereas a GaN thin film grown on a (0001) sapphire substrate was deformed by Vickers indentation in the temperature range 25–800°C. The TEM observations of the deformed crystals indicate that deformation-induced dislocations in 4H-SiC all lie on the (0001) basal plane but depending on the deformation temperature, are one of two types. The dislocations induced by deformation at temperatures above ∼1 100°C are complete, with a Burgers vector, b, of but are all dissociated into two partials bounding a ribbon of stacking fault. On the other 3 hand, the dislocations induced by deformation in the temperature range 550<T<∼ 1100°C were predominantly single leading partials each dragging a stacking fault behind them. From the width of dissociated dislocations in the high-temperature deformed crystals, the stacking fault energy of 4H-SiC has been estimated to be 14.7±2.5 mJ/m2. Vickers indentations of the [0001]-oriented GaN film produced a dense array of dislocations along the three 〈1120〉 directions at all temperatures. The dislocations were slightly curved with their curvature increasing as the deformation temperature increased. Most of these dislocations were found to have a screw nature with their b parallel to 〈1120〉. Also, within the resolution of the weak-beam method, they were not found to be dissociated. Tilting experiment show that these dislocations lie on the {1100} prism plane rather than the easier (0001) glide plane.

Dislocations Produced by Indentation Deformation of HPVE GaN Films

2000 ◽  
Vol 622 ◽  
Author(s):  
M. H. Hong ◽  
P. Pirouz ◽  
P. M. Tavernier ◽  
D. R. Clarke
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Plastic Zone ◽  
Room Temperature ◽  
Prism Plane ◽  
Weak Beam ◽  
Transmission Electron ◽  
Hardness Tests ◽  
Increasing Temperature ◽  
Gan Film

ABSTRACTVickers hardness tests on {0001} and (1120) faces of a relatively thick GaN film grown on a (0001) sapphire substrate have been performed in the temperature range 25-1200°C. The microstructure of the plastic zone around the indentation sites has been investigated by transmission electron microscopy (TEM). At room temperature, the hardness was measured to be 12.3 GPa on the basal plane, and 11.1 GPa on the prism plane. The hardness decreases gradually with increasing temperature up to ∼800°C and then shows a plateau between ∼800 and ∼1050°C after which it decreases again above ∼1100°C. In contrast to the rather straight dislocations produced by room-temperature indentation of the (0001) face, the dislocations generated by indenting the (1120) face at room temperature were curved and in the shape of half-loops emanating from the indentation sites on the prism planes. Such dislocations were not dissociated within the resolution of weak-beam TEM.

Tem Study of Dislocations in Plastically Deformed AlN

1992 ◽  
Vol 242 ◽  
Author(s):  
V. Audurier ◽  
J. L. Demenet ◽  
J. Rabier
Keyword(s):  
Electron Microscopy ◽  
Room Temperature ◽  
Compound Semiconductors ◽  
Burgers Vector ◽  
Weak Beam ◽  
Deformation Substructure ◽  
Transmission Electron ◽  
Doping Effects ◽  
Electronic Doping ◽  
Beam Technique

ABSTRACTAlN ceramics were plastically deformed using uniaxial compression under hydrostatic pressure between room temperature (RT) and 800°C. Deformation microstructures have been studied by Transmission Electron Microscopy (TEM) using the weak beam technique. The deformation substructure at RT is characterized by perfect glide loops with 1/3<1120> Burgers vector in (0001) elongated in the screw direction. When deformation temperature increases, the screw character is associated to cross slip events and dislocation dipolesare found. In the investigated temperature range, slip of dislocations with 1/3<1120> Burgers vector is also evidenced on prismatic planes. Weak beam observations failed to evidence any dislocation splitting. Some of these dislocation properties, similar to those of III-V compound semiconductors, suggest that electronic doping effects could be used to control plastic behaviour of covalent ceramics.

scholarly journals Determination of the Burgers Vector of Twin Boundary Dislocations by Weak Beam Method

1984 ◽  
Vol 48 (5) ◽  
pp. 455-460
Author(s):  
Kun-ichi Miyazawa ◽  
Du-bin Cheng ◽  
Hideo Saito ◽  
Minoru Mori ◽  
Yoichi Ishida
Keyword(s):  
Twin Boundary ◽  
Burgers Vector ◽  
Weak Beam ◽  
Beam Method

Microstructures of straight and wavy interfaces formed in explosively bonded copper single crystals

1986 ◽  
Vol 44 ◽  
pp. 426-427
Author(s):  
Han-ryong Pak ◽  
Chung-wen Chen ◽  
O. T. Inal ◽  
Kali Mukerjee
Keyword(s):  
Single Crystals ◽  
Solid Phase ◽  
Bonding Process ◽  
Transmission Electron ◽  
Plastic Deformation Behavior ◽  
Direct Contrast ◽  
Wavy Interface ◽  
Copper Single Crystals ◽  
Means Of Transmission ◽  
Insight Into

Explosive welding is essentially a solid-phase bonding process, hence any metal can be bonded even if they are totally dissimilar physically and chemically. Our group recently found that a straight interface is superior, with respect to plastic deformation behavior, to a wavy one, in direct contrast to a model that an interlocking structure of a wavy interface produces strong bonds. To obtain some insight into the superiority of such a straight interface, microstructures of copper single crystals (size: 4 x 40 x 130 mm) explosively welded in a parallel standoff configuration are investigated by means of transmission electron microscopy.

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