Experimental Tem and Image Simulation of Dislocations in Ti3A1

1994 ◽  
Vol 364 ◽  
Author(s):  
JÖrg M.K. Wiezorek ◽  
S. A. Court ◽  
C.J. Humphreys
Keyword(s):  
Fine Structure ◽  
Room Temperature ◽  
Stacking Faults ◽  
Antiphase Boundary ◽  
Computational Techniques ◽  
Image Simulation ◽  
Prism Plane ◽  
Weak Beam ◽  
Transmission Electron ◽  
Beam Technique

AbstractThe fine structure and the character of a dislocations on prism planes have been determined for room-temperature deformed polycrystalline Ti3Al using a combination of experimental and computational techniques of transmission electron microscopy (TEM). Within the resolution limits of the weak-beam technique the fine structure of prism plane a dislocations in Ti3Al is found to be planar and to comprise only a single ribbon of antiphase boundary and no experimentally observable stacking faults.

Plasticity, Dislocation Structures and Antiphase Boundary Energies in Fe3Al Single Crystals with Chromium

1996 ◽  
Vol 460 ◽  
Author(s):  
Filip Král ◽  
Peter Schwander ◽  
Gernot Kostorz
Keyword(s):  
Single Crystals ◽  
Room Temperature ◽  
Antiphase Boundary ◽  
Positive Temperature ◽  
Weak Beam ◽  
Dislocation Arrangement ◽  
Transmission Electron ◽  
Direct Measurements ◽  
Critical Resolved Shear Stress ◽  
Beam Technique

ABSTRACTThe influence of Cr additions on the positive temperature dependence of the critical resolved shear stress of Fe3Al is investigated. Single crystals of binary Fe-28 at.% Al and ternary Fe-28 at.% Al-6 at.% Cr with different orientations are deformed in uniaxial compression between room temperature and 1273 K. The dislocation arrangement and the dissociation of superdislocations are studied by transmission electron microscopy using the weak-beam technique. The operative slip systems are discussed on the basis of the direct measurements of the antiphase boundary energies and of the activation volume.

Dislocation Structures in Ni3(Al, Hf)

1996 ◽  
Vol 460 ◽  
Author(s):  
T. Kruml ◽  
B. Viguier ◽  
J. Bonneville ◽  
P. Spätig ◽  
J. L. Martin
Keyword(s):  
Electron Microscopy ◽  
Antiphase Boundary ◽  
Image Simulation ◽  
Compression Tests ◽  
Simulation Techniques ◽  
Weak Beam ◽  
Thin Foils ◽  
Transmission Electron ◽  
Different Temperatures

ABSTRACTSingle crystalline specimens of Ni74.8Al21.9Hf3.3 were subjected to compression tests at different temperatures. Thin foils for transmission electron microscopy observations were prepared from several specimens deformed within and above the yield stress anomaly domain. The dislocation microstructure was studied. The weak beam imaging and image simulation techniques followed by anisotropie elasticity calculations were used for the determination of antiphase boundary energies in both cube and octahedral planes, resulting in values of 237 mJm-2 and 252 mJm-2 respectively. The comparison of the present results with data taken from literature shows the influence of Hf on mechanical properties, dislocation microstructures and APB energies.

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.

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.

The mechanisms of plastic deformation of rapidly solidified Al3Ti and Al67Ni8Ti25 intermetallic compounds.

1988 ◽  
Vol 133 ◽  
Author(s):  
Vijay K. Vasudevan ◽  
Robert Wheeler ◽  
Hamish L. Fraser
Keyword(s):  
Room Temperature ◽  
Considerable Increase ◽  
Stacking Faults ◽  
Temperature Deformation ◽  
Deformation Microstructure ◽  
Partial Dislocations ◽  
Transmission Electron ◽  
The Mean ◽  
Rapidly Solidified ◽  
Mechanisms Of Plastic Deformation

ABSTRACTThe dislocation structures in rapidly solidified Al3Ti with the DO22 structure and the ternary Al-25Ti-8Ni (at.%) alloy with the L12 structure deformed in compression in the temperature range of 25 to 800°C have been studied by transmission electron microscopy. The room temperature deformation microstructure of the Al3Ti compound is characterized by the presence of stacking faults/order twins on {111} planes bounded by partial dislocations with Burgers vector b=1/6<112], as reported by others. At intermediate temperatures, besides the stacking faults, slip is also observed as bands on the {001] plane delineated by dislocations with b=1/2<110] which bound APB's. At 600°C, the reported increase in ductility is associated here with additional slip on the {001)<110], {001)[100] and {001)[010] systems. Dislocations with b=<110] exist as pairs of partial dislocations with b=1/2<110] connected by APB's. The mean separation between the partials was measured to be 30 nm, corresponding to an APB energy of ≍32 mJ.m-2 on the (001) plane. Observations also indicate that the APB energy is anisotropic, i.e., is considerably higher on the {111} planes compared to the {001) plane. The deformation microstructure of the Al-25Ti-8Ni L12 alloy is characterized by slip of dislocations with b=<110> gliding on {111} planes, a major fraction of which exist as dipoles. Following deformation at 300°C, there is essentially no evidence of dissociation of these dislocations, although some dissociated dislocations on (001) having b=l/2<110> are also observed. With an increase in temperature, there is a considerable increase in dislocation activity and strong evidence for 1/2<110> dissociated dislocations is present.

Twin Boundaries and Stacking Faults in Monazite (Monoclinic LaPO4)

2004 ◽  
Vol 819 ◽  
Author(s):  
Randall S. Hay
Keyword(s):  
Room Temperature ◽  
Deformation Twin ◽  
Stacking Faults ◽  
Temperature Deformation ◽  
Formation Mechanisms ◽  
Twin Boundaries ◽  
Partial Dislocations ◽  
Transmission Electron ◽  
Fault Migration ◽  
Lattice Formation

AbstractMonazite (LaPO4) was indented at room temperature. Deformation twin boundaries and stacking faults were characterized by high resolution transmission electron microscopy. Kinked deformation twins were also characterized and analyzed. Three types of stacking faults associated with climb-dissociated partial dislocations were observed. Two were found on twin boundaries, and a third in the lattice. Formation mechanisms are discussed. The superimposition of stacking faults along twin boundaries during deformation twinning and the glide of climb-dissociated partial dislocations allowed by stacking fault migration are discussed. The possible relationship between the formation mechanisms for these defects and the low- temperature recrystallization and self-annealing of defects in monazite is considered.

High Resolution Transmission Electron Microscopy of Proton Implanted Gallium Arsenide

1985 ◽  
Vol 46 ◽  
Author(s):  
D. K. Sadana ◽  
J. M. Zavada ◽  
H. A. Jenkinson ◽  
T. Sands
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Phenomenological Model ◽  
Room Temperature ◽  
Stacking Faults ◽  
High Dose ◽  
Cross Sectional ◽  
Projected Range ◽  
Transmission Electron

AbstractHigh resolution transmission electron microscopy (HRTEM) has been performed on cross-sectional specimens from high dose (1016 cm−2) H+ implanted (100) GaAs (300 keV at room temperature). It was found that annealing at 500°C created small (20-50Å) loops on {111} near the projected range (Rp)(3.2 μm). At 550-600°C, voids surrounded by stacking faults, microtwins and perfect dislocations were observed near the Rp. A phenomenological model explaining the observed results is proposed.

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 Dark-Field Study of Stacking Faults in a Co-Cr-Mo-C Alloy

1976 ◽  
Vol 34 ◽  
pp. 378-379
Author(s):  
Ernest L. Hall
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Field Study ◽  
Previous Investigation ◽  
Stacking Faults ◽  
Aging Treatment ◽  
Dark Field ◽  
Bright Field ◽  
Weak Beam ◽  
Transmission Electron

In a previous investigation (1) of the mechanisms of strengthening in a Co-28 wt% Cr-6 wt% Mo-0.29 wt% C alloy (H.S. 21), it was observed that the fee regions of this alloy were generally heavily faulted, and the density of stacking faults was seen to be dependent upon the time and temperature of the aging treatment after solutionizing. In the present study, weak-beam darkfield transmission electron microscopy was used to examine the interaction of stacking faults on intersecting {111} planes. The alloy was solutionized at 1230°C for 4 hours, quenched in water, and aged at 650°C for 8 hours in order to produce a suitable density of faults. Figure 1 shows a bright-field (BF), weak-beam dark-field (WB DF) pair of micrographs illustrating both the successful and unsuccessful intersection of faults which exist in different ﹛111﹜ planes.

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