Additivity of Hardening by Nanolamellar Structure and Antiphase Domain in Ti-39at%Al Single Crystals

2008 ◽  
Vol 1086 ◽  
Author(s):  
Yuichiro Koizumi ◽  
Yoritoshi Minamino ◽  
Takayuki Tanaka ◽  
Kazuki Iwamoto
Keyword(s):  
Lamellar Structure ◽  
Antiphase Domain ◽  
Dislocation Motion ◽  
Additional Stress ◽  
Slip Direction ◽  
Prism Slip ◽  
Screw Dislocations ◽  
Lamellar Structures ◽  
Mixed Microstructure ◽  
Antiphase Domains

AbstractA mixed microstructure of antiphase domains (APD) and fine lamellar structure were introduced in a Ti-39at%Al single crystal and it was examined whether the APD hardening works even in nano-scaled lamellar structures. The hardness increases with decreasing APD size even where the L is smaller than 100 nm below which the hardening by lamellar refining saturates. The mechanism of the additivity of strengthening by APD and lamellar structure is discussed in the context of the geometries of slip direction, lamellar boundaries and APD boundaries (APDBs). For {1100}<1120> prism slip (the easiest slip system of α2-Ti3Al), the lamellar boundaries are parallel to the slip direction, and therefore they interrupt the motion of screw dislocations effectively. On the other hand, APDBs inclined from lamellar boundaries can effectively obstruct the dislocation motion regardless of the dislocation character because the shear of such APDBs results in the formation of step-like APDBs on the slip-plane and requires additional stress for dislocation motion whereas APDBs parallel to the slip direction can be sheared without forming such a step-like APDB. Accordingly, APDs and lamellar structure can contribute to the strengthening complementarily.

Evolution of Antiphase Domains and γ Lamellae in Ti-39at%Al Single Crystals

2006 ◽  
Vol 980 ◽  
Author(s):  
Yuichiro Koizumi ◽  
Kazuki Iwamoto ◽  
Takayuki Tanaka ◽  
Yoritoshi Minamino ◽  
Nobuhiro Tsuji
Keyword(s):  
Single Crystals ◽  
Structure Formation ◽  
Lamellar Structure ◽  
Lamellar Spacing ◽  
Antiphase Domain ◽  
Single Phase State ◽  
Preferential Nucleation ◽  
Phase Temperature ◽  
Antiphase Domains ◽  
The Moment

AbstractWe studied antiphase domain (APD) growth and lamellar structure formation during isothermal annealing of Ti-39at%Al single crystals at α2+γ dual phase temperature after quenching from α single phase state, intending to obtain a APD/lamellae mixed microstructure and to examine whether such a microstructure provides a strength higher than that obtained only by refining lamellar structure. The effect of plastic deformation prior to the annealing was also examined expecting a acceleration of γ lamellae formation through a preferential nucleation of γ-plates at dislocations. The lower was the annealing temperature, the smaller both the APD size and the lamellar spacing at the moment of a homogeneous lamellar structure formation tended to be, although naturally both the APD growth and the γ lamellae formation were slower. However, the APD size in the homogeneous lamellar structure was no smaller than 400 nm. A structure with finer APDs and finer lamellar structure was obtained by deforming the crystal before annealing since the lamellar structure formation was accelerated and the time for APD growth before the lamellar structure formation was shortened. For instance, a structure with an average lamellar spacing of 88 nm and an average APD size of 214 nm was obtained by deforming the crystals to 10 % plastic strain and subsequently annealing at 1073 K for 1×104 s, while no γ plate was obtained only by such an annealing without deformation.

Effect of Antiphase Domain Boundaries on Prism Slip in Ti3Al Single Crystals

2002 ◽  
Vol 753 ◽  
Author(s):  
Y. Koizumi ◽  
Y. Minamino ◽  
N. Tsuji ◽  
T. Nakano ◽  
Y. Umakoshi
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Yield Stress ◽  
Dislocation Structure ◽  
Antiphase Domain ◽  
Prism Slip ◽  
Domain Boundaries ◽  
Antiphase Domains

ABSTRACTEffect of antiphase domain boundaries (APDBs) on yielding and dislocation structure were investigated in Ti3Al single crystals oriented for prism slip. The yield stress greatly depended on the size of antiphase domains (APDs). The yield stress of Ti3Al with the average APD size of 35nm was about six times higher than that of Ti3Al without APDB. Single dislocations (isolated superpartial dislocations) were observed in the deformed Ti3Al single crystal with APD sizes smaller than 100nm, while superdislocation pairs were observed in those with larger APDs. The mechanism of the interaction between the prism dislocations and APDBs is discussed.

scholarly journals Novel cloaking lamellar structures for a screw dislocation dipole, a circular Eshelby inclusion and a concentrated couple

2020 ◽  
Vol 476 (2241) ◽  
pp. 20200095
Author(s):  
Xu Wang ◽  
Peter Schiavone
Keyword(s):  
Conformal Mapping ◽  
Screw Dislocation ◽  
Lamellar Structure ◽  
Stress Fields ◽  
Uniform Stress ◽  
Dislocation Dipole ◽  
Lamellar Structures ◽  
Eshelby Inclusion ◽  
Mapping Techniques ◽  
Concentrated Couple

Using conformal mapping techniques, we design novel lamellar structures which cloak the influence of any one of a screw dislocation dipole, a circular Eshelby inclusion or a concentrated couple. The lamellar structure is composed of two half-planes bonded through a middle coating with a variable thickness within which is located either the dislocation dipole, the circular Eshelby inclusion or the concentrated couple. The Eshelby inclusion undergoes either uniform anti-plane eigenstrains or uniform in-plane volumetric eigenstrains. As a result, the influence of any one of the dislocation dipole, the circular Eshelby inclusion or the concentrated couple is cloaked in that their presence will not disturb the prescribed uniform stress fields in both surrounding half-planes.

On the Stress Anomaly of γ-TiAl

2000 ◽  
Vol 646 ◽  
Author(s):  
Marc C. Fivel ◽  
Francois Louchet ◽  
Bernard Viguier ◽  
Marc Verdier
Keyword(s):  
Dislocation Motion ◽  
Cross Slip ◽  
Screw Dislocations ◽  
Mesoscopic Simulation ◽  
Temperature Range ◽  
Ordinary Dislocation ◽  
Dislocation Behaviour

ABSTRACTA 3D mesoscopic simulation of dislocation behaviour is adapted to the case of γ-TiAl. It shows that, in the temperature range of the stress anomaly, ordinary dislocation motion essentially proceeds through a series of pinning and unzipping processes on screw dislocations. Pinning points are cross-slip generated jogs, whose density increases with temperature. Unzipping of cusps restores the screw character of the dislocation. The balance between pinning and unzipping becomes increasingly difficult as temperature raises, and results in dislocation exhaustion. All these features agree with the so-called “Local Pinning Unzipping” mechanism.

Computer Simulation of Vacancy Segregation at Antiphase Domain Boundaries During Coarsening

1993 ◽  
Vol 319 ◽  
Author(s):  
Long-Qing Chen
Keyword(s):  
Computer Simulation ◽  
Vacancy Concentration ◽  
Antiphase Domain ◽  
Atomic Diffusion ◽  
Domain Boundaries ◽  
Order Of Magnitude ◽  
Segregation Profile ◽  
Computer Simulation Technique ◽  
Antiphase Domains ◽  
Coarsening Kinetics

AbstractA computer simulation technique based on the Master Equation Method (MEM) is developed for modeling the spatial distribution of vacancies during ordering and subsequent domain coalescence and coarsening. A vacancy mechanism is assumed for the atomic diffusion and the single-site approximation is employed. It is demonstrated that vacancies strongly segregate into the antiphase domain boundaries (APBs) during coarsening, resulting in the vacancy concentration at APBs more than an order of magnitude higher than that inside the ordered domains. As the antiphase domains coarsen, the vacancy concentration at the APBs continues to increase and its spatial s segregation profile moves accompanying the APB migration. The effect of vacancy concentration on the antiphase domain coarsening kinetics is discussed.

Lattice modulation in the hexagonal-type antiphase domain structure of Au–33at.%Cd alloy

1982 ◽  
Vol 15 (2) ◽  
pp. 174-181 ◽  
Author(s):  
Y. Watanbe ◽  
H. Iwasaki
Keyword(s):  
Crystal Structure ◽  
Transition Metal Dichalcogenides ◽  
Antiphase Domain ◽  
Charge Density Waves ◽  
Physical Significance ◽  
Intensity Data ◽  
X Ray Diffraction ◽  
X Ray ◽  
Metal Dichalcogenides ◽  
Antiphase Domains

The crystal structure of an ordered Au–33at.%Cd alloy has been reinvestigated by X-ray diffraction. Least-squares refinement using single-crystal intensity data collected by photographic methods has shown that mixed occupation by the two kinds of atoms preferentially occurs in the atomic sites located near the boundaries of the hexagonal antiphase domains, confirming the results obtained by electron diffraction [Hirabayashi, Yamaguchi, Hiraga, Ino, Sato & Toth (1970). d. Phys. Chem. Solids, 31, 77–94]. The refinement has also shown that many of the atoms are periodically displaced from the normal positions of the fundamental h.c.p. lattice. The physical significance of the occupancy and displacement modulations is discussed. The latter bears a resemblance to the motion of cations in the transition-metal dichalcogenides and the direction of the displacements in the alloy can be explained if charge-density waves synchronizing with the occupancy waves are assumed to exist.

RELATION OF LAMELLAR STRUCTURE AND SHEAR STRESS OF DYNAMIC PM-ER FLUIDS

2011 ◽  
Vol 25 (07) ◽  
pp. 971-977 ◽  
Author(s):  
D. K. LIU ◽  
C. LI ◽  
J. YAO ◽  
L. W. ZHOU ◽  
J. P. HUANG
Keyword(s):  
Molecular Dynamics ◽  
Shear Stress ◽  
Lamellar Structure ◽  
Inverse Correlation ◽  
Dynamics Simulation ◽  
Rheological Characteristics ◽  
Lamellar Structures ◽  
Dynamic Rheological Behavior ◽  
Moving Particle ◽  
Er Fluids

To understand the dynamic rheological behavior of polar molecular electrorheological (PMER) fluids, the shear stress and viscosity of the colloids are compared with the parameters of their lamellar structures which are obtained simultaneously with the rheological characteristics using an electrorheoscope. The results of the experiments and molecular dynamics simulation indicate that the shear stress is mainly contributed by the moving particle rings, and there is an inverse correlation between the width of the moving particle rings and the shear stress.

Engineering oriented hierarchical lamellar structures in SBS/PS blends via a pressure-induced flow field

RSC Advances ◽  
2016 ◽  
Vol 6 (26) ◽  
pp. 21546-21554 ◽  
Author(s):  
Sen Zhang ◽  
Xiaoling Feng ◽  
Shu Zhu ◽  
Shiwei Wang ◽  
Da Wang ◽  
...  
Keyword(s):  
Flow Field ◽  
Polymer Blend ◽  
Layered Structure ◽  
Lamellar Structure ◽  
Lamellar Structures ◽  
Induced Flow ◽  
Styrene Butadiene Styrene ◽  
Styrene Butadiene ◽  
Butadiene Styrene

A hierarchical layered structure was generated using a polymer blend of polystyrene/poly(styrene–butadiene–styrene). Benefiting from the hierarchical lamellar structure, the resulting strength, stiffness and toughness were simultaneously enhanced.

scholarly journals Breakdown of the Schmid Law in BCC Molybdenum Related to the Effect of Shear Stress Perpendicular to the Slip Direction

2005 ◽  
Vol 482 ◽  
pp. 123-126 ◽  
Author(s):  
R. Gröger ◽  
V. Vitek
Keyword(s):  
Shear Stress ◽  
Dislocation Motion ◽  
Peierls Stress ◽  
Shear Stresses ◽  
Slip Direction ◽  
Burgers Vector ◽  
Long Time ◽  
Schmid Factor ◽  
Critical Resolved Shear Stress ◽  
Negative Sense

The breakdown of the Schmid law in bcc metals has been known for a long time. The asymmetry of shearing in the slip direction 〈111〉 in the positive and negative sense, respectively, commonly identified with the twinning-antitwinning asymmetry, is undoubtedly one of the reasons. However, effect of stress components other than the shear stress in the slip direction may be important. In this paper we investigate by atomistic modeling the effect of shear stresses perpendicular to the Burgers vector on the glide of a/2〈111〉 screw dislocations. We show that these shear stresses can significantly elevate or reduce the critical resolved shear stress (CRSS) in the direction of the Burgers vector needed for the dislocation motion, i.e. the Peierls stress. This occurs owing to the changes of the core induced by these stresses. This effect may be the reason why slip systems with smaller Schmid factors may be preferred over that with the largest Schmid factor.

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