Antiphase Domain Boundary Tubes in Ordered Alloys

1986 ◽  
Vol 81 ◽  
Author(s):  
P.M. Hazzledine ◽  
Peter Hirsch
Keyword(s):  
Electron Microscopy ◽  
Work Hardening ◽  
Domain Boundary ◽  
Antiphase Domain ◽  
Orientation Dependence ◽  
Cross Slip ◽  
Proof Stress ◽  
Screw Dislocations ◽  
Ordered Alloys ◽  
Edge Dislocations

AbstractAPB tubes have been observed in both a B2 and an L12 ordered alloy by means of weak beamtransmission electron microscopy. The tubes are attached to near—edge dislocations, either to single superdislocations or to superdipoles. The majority appearto have been formed by cross slip of screw dislocations. A computer model of the cross slip process in B2 alloys is described. The tubes formed by cross slip drag on edge dislocations and are capable in principle of explaining the extra work hardening shown by ordered over disordered crystals. The temperature and orientation dependence of the work hardening are similar to those of the proof stress which is also thought to be controlled by cross slip. This new mechanism of work hardening is shown to give order of magnitudeagreement with experiment.

Formation of antiphase-domain boundary tubes in B2 ordered alloys by cross-slip and annihilation of screw dislocations

1987 ◽  
Vol 56 (6) ◽  
pp. 799-813 ◽  
Author(s):  
C. T. Chou ◽  
P. M. Hazzledine ◽  
P. B. Hirsch ◽  
G. R. Anstis
Keyword(s):  
Domain Boundary ◽  
Antiphase Domain ◽  
Cross Slip ◽  
Screw Dislocations ◽  
Ordered Alloys

Electron microscopy of antiphase domain boundary tubes in deformed ordered alloys

1983 ◽  
Vol 387 (1792) ◽  
pp. 91-104 ◽  
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Flow Stress ◽  
Domain Boundary ◽  
Antiphase Domain ◽  
Dark Field ◽  
Al Alloy ◽  
Ordered Alloys ◽  
Microscope Images ◽  
Dark Field Electron

Antiphase domain boundary (APB) tubes have been observed in a slightly deformed Fe–30.5 at. % Al alloy in dark field electron microscope images taken in superlattice reflexions. The image contrast theory has been developed and accounts satisfactorily for the nature of the APB tube contrast observed. The contrast theory is used to estimate the heights of the tubes. The widths of the tubes range from 20 to 50 ņ, and the measured heights are in the range of one to six times the elementary height. Evidence is presented that tubes are generated by the Vidoz & Brown (1962) mechanism and by a mechanism of cross-slip and annihilation of screw superdislocations. The possible effects of tubes on flow stress are discussed.

Dislocation Structures and Anomalous Yielding in Ordered Alloys

1990 ◽  
Vol 213 ◽  
Author(s):  
P. M. Hazzledine ◽  
Y. Q. Sun
Keyword(s):  
Mechanical Properties ◽  
Electron Microscope ◽  
Strain Rate ◽  
Yield Stress ◽  
Work Hardening ◽  
Screw Dislocations ◽  
Ordered Alloys ◽  
Work Hardening Rate ◽  
Initial Work ◽  
Edge Dislocations

ABSTRACTThe strain, strain rate and temperature dependencies of the yield stresses of the model L12 materials Ni3Al, Ni3Ga and Co3Ti are described, as well as two associated properties, the initial work-hardening rate and the inverted creep. These mechanical properties, the electron microscope observations of <110> {111} APB coupled slip and the violations of Schmid's laws point to glissile-sessile-glissile transitions by cross slip of screw dislocations as the explanation for the yield stress anomaly. Similar explanations are probable for h.c.p. Be, B2 CoTi and tetragonal TiAl and MoSi2. A different kind of model, based on the behavior of edge dislocations is required for h.c.p. Mg, B2 CuZn and DO19 Ti3Al.

Nucleation of Disorder in Fe3Al Alloys

1967 ◽  
Vol 25 ◽  
pp. 312-313
Author(s):  
P. R. Swann ◽  
W. R. Duff ◽  
R. M. Fisher
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Annealing Temperature ◽  
Antiphase Domain ◽  
Effect Of Temperature ◽  
Domain Structures ◽  
Transmission Electron ◽  
Domain Boundaries ◽  
Higher Temperature ◽  
The One

Recently we have investigated the phase equilibria and antiphase domain structures of Fe-Al alloys containing from 18 to 50 at.% Al by transmission electron microscopy and Mössbauer techniques. This study has revealed that none of the published phase diagrams are correct, although the one proposed by Rimlinger agrees most closely with our results to be published separately. In this paper observations by transmission electron microscopy relating to the nucleation of disorder in Fe-24% Al will be described. Figure 1 shows the structure after heating this alloy to 776.6°C and quenching. The white areas are B2 micro-domains corresponding to regions of disorder which form at the annealing temperature and re-order during the quench. By examining specimens heated in a temperature gradient of 2°C/cm it is possible to determine the effect of temperature on the disordering reaction very precisely. It was found that disorder begins at existing antiphase domain boundaries but that at a slightly higher temperature (1°C) it also occurs by homogeneous nucleation within the domains. A small (∼ .01°C) further increase in temperature caused these micro-domains to completely fill the specimen.

The observation of solutions in Ni3Nb

1988 ◽  
Vol 46 ◽  
pp. 540-541
Author(s):  
Z.M. Wang ◽  
J.P. Zhang
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Phase Modulation ◽  
High Resolution Electron Microscopy ◽  
Antiphase Domain ◽  
Boundary Area ◽  
Matrix Type ◽  
Resolution Electron ◽  
Domain Boundaries ◽  
Kontorova Model

High resolution electron microscopy reveals that antiphase domain boundaries in β-Ni3Nb have a hexagonal unit cell with lattice parameters ah=aβ and ch=bβ, where aβ and bβ are of the orthogonal β matrix. (See Figure 1.) Some of these boundaries can creep “upstairs” leaving an incoherent area, as shown in region P. When the stepped boundaries meet each other, they do not lose their own character. Our consideration in this work is to estimate the influnce of the natural misfit δ{(ab-aβ)/aβ≠0}. Defining the displacement field at the boundary as a phase modulation Φ(x), following the Frenkel-Kontorova model [2], we consider the boundary area to be made up of a two unit chain, the upper portion of which can move and the lower portion of the β matrix type, assumed to be fixed. (See the schematic pattern in Figure 2(a)).

TEM investigation of defect reduction and etch pit formation in GaN

2003 ◽  
Vol 798 ◽  
Author(s):  
Angelika Vennemann ◽  
Jens Dennemarck ◽  
Roland Kröger ◽  
Tim Böttcher ◽  
Detlef Hommel ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Dislocation Density ◽  
Line Tension ◽  
Threading Dislocations ◽  
Dislocation Loops ◽  
Etch Pits ◽  
Defect Reduction ◽  
Transmission Electron ◽  
Order Of Magnitude ◽  
Edge Dislocations

ABSTRACTGaN samples of this study were chemically wet etched to gain easier access to the dislocation sturcture. The scanning electron microscopy and transmission electron microscopy investigations revealed four different types of etch pits. After brief etching, several dislocations with screw component showed large etch pits, which may be correlated with the core of the screw dislocation. By means of SiNx micromasking the dislocation density could be reduced by more than one order of magnitude. The reduction of threading dislocations in the SiNx region in GaN grown on 〈0001〉 sapphire is due to bending of the threading dislocations into the {0001} plane, such that they form dislocation loops if they meet dislocations with opposite Burgers vectors. Accordingly, the achievable reduction of the dislocation density is limited by the probability that these dislocations interact. Edge dislocations bend more easily on account of their low line tension. This results in a preferential bending and reduction of dislocations with edge character.

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