Hydrogen-enhanced dislocation velocities in Ni3Al single crystals

2000 ◽  
Vol 15 (1) ◽  
pp. 7-9 ◽  
Author(s):  
C. B. Jiang ◽  
S. Patu ◽  
Q. Z. Lei ◽  
C. X. Shi
Keyword(s):  
Activation Energy ◽  
Shear Stress ◽  
Single Crystals ◽  
Room Temperature ◽  
Dislocation Motion ◽  
Dislocation Velocity ◽  
Dislocation Mobility ◽  
Preliminary Results ◽  
Etch Pit

The average dislocation velocity in hydrogenated Ni3Al single crystals was directly measured as a function of resolved shear stress (RSS) at room temperature (293 K) by the etch-pit technique. It was found that the dislocation velocity with hydrogen is about 5–25 times faster than that without hydrogen for the same RSS, and hydrogen decreases activation energy for dislocation motion in Ni3Al single crystals. The reason hydrogen can enhance dislocation velocity in this compound is briefly discussed. These preliminary results quantitatively provide the first evidence of hydrogen-enhancing dislocation mobility in Ni3Al material.

Room Temperature Deformation in “Soft” Orientation Nial Single Crystals

1990 ◽  
Vol 213 ◽  
Author(s):  
R.D. Field ◽  
D.F. Lahrman ◽  
R. Darolia
Keyword(s):  
Shear Stress ◽  
Elevated Temperature ◽  
Single Crystals ◽  
Room Temperature ◽  
Dislocation Motion ◽  
Temperature Deformation ◽  
Slip Planes ◽  
Schmid Factor ◽  
Critical Resolved Shear Stress ◽  
Active Slip

ABSTRACTA detailed study of deformation of NiAl single crystals in two soft orientations, <110> and <111>, has been conducted. The Schmid factor favors {100} slip in the former and {110} slip in the latter. Detailed dislocation analysis, critical resolved shear stress measurements, and slip trace analysis have been performed to determine the nature of dislocation motion and interactions in this material. Particular attention is given to prismatic loops formed during deformation, since the shapes of these loops reveal the active slip planes. Similar loop morphologies observed in elevated temperature [001] oriented tensile specimens are also discussed.

Dislocation Mobility in HCL-Doped Ice

1994 ◽  
Vol 375 ◽  
Author(s):  
Xiaohong Hu ◽  
Kunlun Jia ◽  
Fuping Liu ◽  
Ian Baker ◽  
David Black
Keyword(s):  
Single Crystals ◽  
Dislocation Velocity ◽  
Dislocation Mobility ◽  
Philosophical Magazine ◽  
X Ray ◽  
Temperature Range ◽  
Basal Dislocation

AbstractDislocation velocities have been measured in both lightly and heavily HCl-doped ice single crystals using synchrotron-based, monochromatic X-ray topography. In the temperature range −10°C to −30°C, a concentration of ˜1 × 10−6M was found not to affect the mobility of either 60° or screw basal dislocations, confirming the earlier observations of C. Shearwood and R. W. Whitworth [Philosophical Magazine A65, 1992, 85]. However, heavier doping (˜1.9 × 10−4M) increased the basal dislocation velocity, compared to pure ice, by a factor of 2.6 at −16.4°C.

Plastic Deformations in L10-Ordered Single Crystals with their c/a Ratios Less than Unity

2007 ◽  
Vol 561-565 ◽  
pp. 459-462
Author(s):  
Katsushi Tanaka ◽  
Hiromitsu Ide ◽  
Yoshinori Sumi ◽  
Kyosuke Kishida ◽  
Haruyuki Inui
Keyword(s):  
Shear Stress ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Room Temperature ◽  
The Other ◽  
Compressive Deformation ◽  
Positive Temperature ◽  
Plastic Deformations ◽  
Temperature Range ◽  
Critical Resolved Shear Stress

Compressive deformation of L10-ordered single crystals of FePd whose c/a ratio less than unity have been investigated from room temperature to 823 K. The results show that the critical resolved shear stress (CRSS) for octahedral glide of ordinary dislocations is smaller than that of super-lattice dislocations in all the temperature range investigated, that is the opposite sense to the case of Ti-56 mol% Al. The CRSS for ordinary dislocations virtually independent to the temperature. On the other hand, the CRSS for super dislocations exhibits a weak positive temperature dependence from room temperature up to 573 K and decreases in higher temperatures.

Influence of Dislocation Mobility on Room and High Temperature Ductility of -Oriented Nial Single Crystals

1994 ◽  
Vol 364 ◽  
Author(s):  
M. A. Morris ◽  
J. P. Perez ◽  
R. Darolia
Keyword(s):  
High Temperature ◽  
Single Crystals ◽  
Room Temperature ◽  
Tensile Tests ◽  
Slip Systems ◽  
Dislocation Mobility ◽  
Screw Dislocations ◽  
Large Density ◽  
Thin Foils

AbstractThe dislocation configurations produced by room and high temperature compression of <100> oriented single crystals of binary NiAl and in those containing iron and hafnium additions have been analysed and compared to those obtained by hardness indentation and TEM insitu tensile tests. Kinking occurs during room temperature compression such that <100> dislocations are activated in all cases but the iron-containing alloy also exhibited a large density of <111> screw dislocations. The latter however, appear immobile when they are created by hardness indentations of thin foils, while only pile-ups of <100> segments can propagate. Similarly, although different slip systems are present after high temperature compression, only <100> dislocation segments have been confirmed to be mobile after room temperature hardness indentation of these predeformed thin foils. The improvement in ductility observed at room temperature in the predeformed specimens of the binary and the iron containing alloys has been attributed to the increased production of these mobile <100> dislocations.

scholarly journals The Internal Friction of Single Crystals, Bicrystals and Polycrystals of Pure Magnesium

2015 ◽  
Vol 60 (1) ◽  
pp. 371-375 ◽  
Author(s):  
W.B. Jiang ◽  
Q.P. Kong ◽  
L.B. Magalas ◽  
Q.F. Fang
Keyword(s):  
Activation Energy ◽  
Internal Friction ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Single Crystals ◽  
Room Temperature ◽  
Internal Friction Peak ◽  
Self Diffusion ◽  
Boundary Relaxation ◽  
The Difference

Abstract The internal friction of magnesium single crystals, bicrystals and polycrystals has been studied between room temperature and 450°C. There is no internal friction peak in the single crystals, but a prominent relaxation peak appears at around 160°C in polycrystals. The activation energy of the peak is 1.0 eV, which is consistent with the grain boundary self-diffusion energy of Mg. Therefore, the peak in polycrystals can be attributed to grain boundary relaxation. For the three studied bicrystals, the grain boundary peak temperatures and activation energies are higher than that of polycrystals, while the peak heights are much lower. The difference between the internal friction peaks in bicrystals and polycrystals is possibly caused by the difference in the concentrations of segregated impurities in grain boundaries.

Plastic Deformations in Single Crystals of FePd with the L10 Structure

2008 ◽  
Vol 1128 ◽  
Author(s):  
Katsushi Tanaka ◽  
Wang Chen ◽  
Kyosuke Kishida ◽  
Norihiko L. Okamoto ◽  
Haruyuki Inui
Keyword(s):  
Plastic Deformation ◽  
Shear Stress ◽  
Temperature Dependence ◽  
Single Crystals ◽  
Yield Stress ◽  
Room Temperature ◽  
Positive Temperature ◽  
Plastic Deformations ◽  
L10 Structure ◽  
Critical Resolved Shear Stress

AbstractCompressive deformations of L10-ordered single crystals of FePd have been investigated from room temperature to 873 K. The critical resolved shear stress for superlattice dislocations is hard to determine resulting from buckling that occurs after a small amount of conventional plastic deformation. The CRSS for superlattice dislocations determined from yield stress is significantly larger than that of ordinary dislocations. The CRSS for octahedral glide of ordinary and superlattice dislocations are virtually independent of the temperature, and the positive temperature dependence of the yield stress is not observed for both, ordinary and superlattice dislocations, by the present experiments.

Anisotropy in the hardness of single crystals

1971 ◽  
Vol 322 (1548) ◽  
pp. 73-88 ◽  
Keyword(s):  
Crystal Structure ◽  
Shear Stress ◽  
Single Crystals ◽  
Dislocation Motion ◽  
Slip Systems ◽  
Maximum Hardness ◽  
Indentation Process ◽  
Wide Range ◽  
Knoop Indentation ◽  
Active Slip

The results of this work, and those published by other researchers who have used Knoop indentation measurements, confirm that the nature of anisotropy in hardness is essentially determined by the crystal structure and the primary slip systems which accommodate dislocation motion during indentation. Materials belonging to the same class of crystal structure and having common slip systems possess similar anisotropic properties. The varying extent of work-hardening or fracture, associated with indentations, does not appear to influence the anisotropy— although twinning on the basal planes of hexagonal closepacked metals may have a significant effect. An analysis of the indentation process is presented which establishes a clear relationship between the ‘effective resolved shear stress’ (t 0 '), in the bulk of the crystal beneath the indenter, and the observed hardness. Directions which correspond to the minimum values of t' e , on specific crystallographic surfaces, are those of maximum hardness and conversely. The analysis is shown to be equally applicable to a wide range of crystalline solids including nonmetallic materials, of various crystal structure, and typical f.c.c., b.c.c. and c.p.h. metals. Finally, anisotropy in hardness can be used to identify active slip systems in those crystals where it is possible for dislocations to move on more than one system.

DYNAMICS OF A DISLOCATION SET IN MOTION BY AN EXTERNAL STRESS

2002 ◽  
Vol 13 (01) ◽  
pp. 97-105 ◽  
Author(s):  
M. ROBLES ◽  
L. PERONDI ◽  
K. KASKI
Keyword(s):  
Shear Stress ◽  
Dislocation Motion ◽  
External Stress ◽  
Atomic Scale ◽  
Dislocation Velocity ◽  
Two Dimensional ◽  
Tracking Method ◽  
Stress Pulse ◽  
Lennard Jones ◽  
Dynamics Simulations

The relation between dislocation velocity and resolved shear stress is studied computationally at the atomic scale using Molecular Dynamics simulations in a two-dimensional Lennard–Jones system. Mimicking a well known experimental technique, we apply a calibrated stress pulse to a system with a single dislocation and follow with a run-time graphics tool and displacement-field based tracking method, the dislocation motion caused by momentum transfer from an externally generated stress pulse. The empirically suggested power law relation between dislocation velocity and resolved shear stress seems to hold also in the atomic scale.

Electron Paramagnetic Resonance in Cu2O Compared with Other Semiconducting Properties

1971 ◽  
Vol 49 (10) ◽  
pp. 1275-1283 ◽  
Author(s):  
J. C. W. Taylor ◽  
F. L. Weichman ◽  
R. E. D. McClung
Keyword(s):  
Activation Energy ◽  
Electron Paramagnetic Resonance ◽  
Single Crystals ◽  
Room Temperature ◽  
Starting Material ◽  
Paramagnetic Resonance ◽  
Semiconducting Properties ◽  
Wide Range ◽  
Temperature Activation ◽  
Electron Paramagnetic

Electron paramagnetic resonance spectra have been observed in single crystals of Cu2O at 4.2 °K. Six samples cut from the same starting material were individually heated under a wide range of vacuum conditions and comparison was made between the observed e.p.r. spectrum and the luminescence, activation energy, and photoconductivity in the same sample. No direct relationships between e.p.r. spectra and the luminescence and photoconductivity were found although a good correlation between the complexity of the e.p.r. spectra and the room temperature activation energy was observed.

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