Slip Systems in Ni3(Al, Ti) At Temperatures Above the Peak in Flow Stress

1988 ◽  
Vol 133 ◽  
Author(s):  
Y. Q. Sun ◽  
P. M. Hazzledine
Keyword(s):  
Flow Stress ◽  
Single Crystals ◽  
Deformation Behaviour ◽  
Slip Systems ◽  
Intermetallic Alloys ◽  
Weak Beam ◽  
Cube Plane ◽  
Ordered Intermetallic ◽  
Beam Technique

ABSTRACTDislocations in single crystals of Ni3(Al, Ti) deformed at temperatures above the peak in flow stress have been studied by the TEM “weak-beam” technique. <110> dislocations on the primary cube plane are mostly of edge character, and they have been observed to transform into “super” Lomer- Cottrell locks. <100> dislocations, by contrast, are principally of 45° character. They are believed also to become immobilized by dissociation on {111} planes. Properties of both dislocations on cube planes are discussed and are related to the deformation behaviour of L12ordered intermetallic alloys.

Creep of Anomalous Ni3Ga

1996 ◽  
Vol 460 ◽  
Author(s):  
M J Lunt ◽  
Y Q Sun
Keyword(s):  
Yield Stress ◽  
Creep Strength ◽  
Rapid Decrease ◽  
Steady State Creep ◽  
Intermetallic Alloys ◽  
Creep Tests ◽  
Screw Dislocations ◽  
Cube Plane ◽  
Ordered Intermetallic ◽  
Inverse Creep

ABSTRACTNi3Ga is among a number of LI2 ordered intermetallic alloys whose yield stress increases with temperature. In this work we have examined the creep strength of [123] and [001] oriented Ni3Ga specimens in the temperature regime of the yield stress anomaly and confirmed that the creep strength shows the normal rapid decrease with temperature. Inverse creep occurs in the [001] specimens where slip is on the {111} planes only. [123] specimens exhibit steady-state creep and slip line and TEM observations have shown slip on the cube plane and dislocations of both <110> and <100> Burgers vectors are present. We have carried out creep tests of prestrained [123] samples and demonstrated that the storage of primary <110> {111} screw dislocations, locked in the Kear-Wilsdorf configuration, has no effect on creep.

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.

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.

Transmission Electron Microscope Observation of Dislocations in Ordered Intermetallic Alloys and the Flow Stress Anomaly

1988 ◽  
Vol 133 ◽  
Author(s):  
Patrick Veyssière
Keyword(s):  
Electron Microscope ◽  
Flow Stress ◽  
Electron Microscope Observation ◽  
Intermetallic Alloys ◽  
Present Contribution ◽  
Transmission Electron Microscope Observation ◽  
Transmission Electron ◽  
Ordered Alloys ◽  
Ordered Intermetallic ◽  
Deformation Modes

ABSTRACTIt is only within the last five years that, with the increasing interest of several specialized groups, the amount of accurate TEM information on dislocations in ordered alloys, and in particular in theL12 structure, has become significant. Our knowledge on superdislocation cores related todeformation under various temperature and deformation modes, is now sufficiently documented in order to be critically reviewed and this is the object of the present contribution.

Modeling of the Dislocation Dynamics in Ni3Al and the Flow Stress Anomaly

1996 ◽  
Vol 460 ◽  
Author(s):  
B. Devincre ◽  
P. Veyssiere ◽  
L. Kubin ◽  
G. Saada Lem
Keyword(s):  
Flow Stress ◽  
Single Crystals ◽  
Plastic Flow ◽  
Low Temperatures ◽  
Theoretical Models ◽  
Dislocation Dynamics ◽  
Mesoscopic Scale ◽  
Dislocation Glide ◽  
Cube Plane ◽  
Temperature Regimes

ABSTRACTNi3Al single crystals are known to exhibit a flow stress anomaly between 200 and 800K. The purpose of our work is to examine such an anomaly by means of a simulation of the dislocation dynamics at a mesoscopic scale. The simulation basic rules are: i) the dislocation glide in {111} octahedral planes, ii) the conditions at which screw lines are locked and unlocked by the formation of Kear-Wilsdorf locks, iii) the mobility of jogs in the {100} cube plane. Our results suggest that two different temperature regimes occur in the domain of the anomaly. At low temperatures, the plastic flow is governed by kink bow-out, itself a function of the kink length. At high temperatures, the plastic flow is governed by the unlocking of the weakest Kear-Wilsdorf locks in the microstructure. These outcomes of the simulation are discussed in relation with the existing theoretical models of the flow stress anomaly.

Dislocation Substructures Produced During Tensile, Creep, and Fatigue Deformation of Ti3Al at 700°C

1977 ◽  
Vol 35 ◽  
pp. 272-273
Author(s):  
S. M. L. Sastry
Keyword(s):  
Intermetallic Compound ◽  
Strain Rate ◽  
Tensile Creep ◽  
Slip Systems ◽  
Slip Vector ◽  
Superlattice Structure ◽  
Slip Activity ◽  
Dislocation Arrangement ◽  
Ordered Intermetallic ◽  
Tangled Dislocation

Ti3Al is an ordered intermetallic compound having the DO19-type superlattice structure. The compound exhibits very limited ductility in tension below 700°C because of a pronounced planarity of slip and the absence of a sufficient number of independent slip systems. Significant differences in slip behavior in the compound as a result of differences in strain rate and mode of deformation are reported here.Figure 1 is a comparison of dislocation substructures in polycrystalline Ti3Al specimens deformed in tension, creep, and fatigue. Slip activity on both the basal and prism planes is observed for each mode of deformation. The dominant slip vector in unidirectional deformation is the a-type (b) = <1120>) (Fig. la). The dislocations are straight, occur for the most part in a screw orientation, and are arranged in planar bands. In contrast, the dislocation distribution in specimens crept at 700°C (Fig. lb) is characterized by a much reduced planarity of slip, a tangled dislocation arrangement instead of planar bands, and an increased incidence of nonbasal slip vectors.

TEM Study of a Tilt Boundary in Hot-Pressed Silicon

1981 ◽  
Vol 39 ◽  
pp. 160-161
Author(s):  
C. B. Carter ◽  
J. Rose ◽  
D. G. Ast
Keyword(s):  
Electron Diffraction ◽  
Imaging Technique ◽  
Interface Structure ◽  
Large Area ◽  
Weak Beam ◽  
Lattice Fringe ◽  
Electron Diffraction Technique ◽  
Tilt Boundaries ◽  
Beam Technique ◽  
Twist Boundaries

The hot-pressing technique which has been successfully used to manufacture twist boundaries in silicon has now been used to form tilt boundaries in this material. In the present study, weak-beam imaging, lattice-fringe imaging and electron diffraction techniques have been combined to identify different features of the interface structure. The weak-beam technique gives an overall picture of the geometry of the boundary and in particular allows steps in the plane of the boundary which are normal to the dislocation lines to be identified. It also allows pockets of amorphous SiO2 remaining in the interface to be recognized. The lattice-fringe imaging technique allows the boundary plane parallel to the dislocation to be identified. Finally the electron diffraction technique allows the periodic structure of the boundary to be evaluated over a large area - this is particularly valuable when the dislocations are closely spaced - and can also provide information on the structural width of the interface.

A Many-Beam Technique for Enhanced Resolution of Partial Dislocations

1972 ◽  
Vol 30 ◽  
pp. 646-647
Author(s):  
J. M. Oblak ◽  
B. H. Kear
Keyword(s):  
Phase Shift ◽  
Field Method ◽  
Dark Field ◽  
Bright Field ◽  
Field Technique ◽  
Weak Beam ◽  
Partial Dislocations ◽  
Enhanced Resolution ◽  
Nickel Base ◽  
Beam Technique

The “weak-beam” and systematic many-beam techniques are the currently available methods for resolution of closely spaced dislocations or other inhomogeneities imaged through strain contrast. The former is a dark field technique and image intensities are usually very weak. The latter is a bright field technique, but generally use of a high voltage instrument is required. In what follows a bright field method for obtaining enhanced resolution of partial dislocations at 100 KV accelerating potential will be described.A brief discussion of an application will first be given. A study of intermediate temperature creep processes in commercial nickel-base alloys strengthened by the Ll2 Ni3 Al γ precipitate has suggested that partial dislocations such as those labelled 1 and 2 in Fig. 1(a) are in reality composed of two closely spaced a/6 <112> Shockley partials. Stacking fault contrast, when present, tends to obscure resolution of the partials; thus, conditions for resolution must be chosen such that the phase shift at the fault is 0 or a multiple of 2π.

Dislocation structures around SiO2 Particles in aged Cu-Cr-SiO2

1978 ◽  
Vol 36 (1) ◽  
pp. 594-595
Author(s):  
N.J. Long ◽  
M.H. Loretto ◽  
C.H. Lloyd
Keyword(s):  
Flow Stress ◽  
Single Crystals ◽  
Room Temperature ◽  
Thin Foil ◽  
Age Hardening ◽  
Dispersion Strengthening ◽  
Accurate Picture ◽  
The Matrix ◽  
Very High ◽  
Good Agreement

IntroductionThere have been several t.e.m. studies (1,2,3,4) of the dislocation arrangements in the matrix and around the particles in dispersion strengthened single crystals deformed in single slip. Good agreement has been obtained in general between the observed structures and the various theories for the flow stress and work hardening of this class of alloy. There has been though some difficulty in obtaining an accurate picture of these arrangements in the case when the obstacles are large (of the order of several 1000's Å). This is due to both the physical loss of dislocations from the thin foil in its preparation and to rearrangement of the structure on unloading and standing at room temperature under the influence of the very high localised stresses in the vicinity of the particles (2,3).This contribution presents part of a study of the Cu-Cr-SiO2 system where age hardening from the Cu-Cr and dispersion strengthening from Cu-Sio2 is combined.

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