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.

Deformation and Dislocation Structure of Ti3AI Single Crystals

1990 ◽  
Vol 186 ◽  
Author(s):  
Y. Minonishi
Keyword(s):  
Slip System ◽  
Single Crystals ◽  
Yield Stress ◽  
Dislocation Structure ◽  
Deformation Characteristics ◽  
Prism Slip ◽  
Pyramidal Slip ◽  
Pure Metals

AbstractDeformation characteristics of Ti3A1 single crystals has been examined as a function of orientation and temperature. This paper mainly describes the result of compression along the c axis. In this orientation, the yield stress increases from 300 to 1100K, decreasing rapidly thereafter. The slip system activated are {1121}<1126> and dislocations observed are nearly of edge character. The anomaly is discussed in comparison with the behavior of other intermetallics and pure metals. An important role this pyramidal slip plays in polycrystalline ductility of Ti3Al is shown in the light of the briefly described results of the prism slip.

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.

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.

Dislocation Structure in Single Crystal L1o Type Ti-Al-V Compound

1990 ◽  
Vol 213 ◽  
Author(s):  
Y.D. Hahn ◽  
Z.X. Li ◽  
S.H. Whang ◽  
T. Kawabata
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
High Temperatures ◽  
Dislocation Structure ◽  
The Other ◽  
Dislocation Loops ◽  
Single Slip ◽  
Pile Up ◽  
Favorable Configuration ◽  
Dipole Form

ABSTRACTSingle Crystals of L1o type Ti44Al54V2 alloy were deformed at high temperatures and various orientations. The dislocations thus produced by single slip were studied by TEM. 1/2<110] dislocations produced at 1073 K consist of dislocation loops and curled dislocations with spiral segments, which is in agreement with those shown in the polycrystalline Ti-Al-V, and -Nb alloys deformed under the same conditions. The normal dislocations produced at 873 K pile up in groups, each of which contains several straight dislocations with a screw character. On the other hand, the majority of superdislocations produced at 873 K were found in a dipole form, indicating that the dipole is a favorable configuration at this temperature.

Parameters of Dislocation Structure and Work Hardening of Ni3Ge

2004 ◽  
Vol 842 ◽  
Author(s):  
N. A. Koneva ◽  
Yu.V. Solov'eva ◽  
V. A. Starenchenko ◽  
E. V. Kozlov
Keyword(s):  
Single Crystals ◽  
Yield Stress ◽  
Dislocation Structure ◽  
Temperature Anomaly ◽  
Friction Stress ◽  
Orientation Dependence ◽  
Compression Tests ◽  
Quantitative Measurements ◽  
Different Temperatures ◽  
Scalar Dislocation Density

ABSTRACTOrientation dependence of the yield stress temperature anomaly in Ni3Ge single crystals with the L12 structure was investigated during compression tests. The measurements were carried out in the 4.2 K-1000 K temperature interval for two orientations of single crystals, [001] and [234]. The dislocation structure was studied by TEM. Quantitative measurements of different parameters of dislocation structure were carried out. The values of the scalar dislocation density, ρ, were determined for different temperatures in the deformation interval from the yield stress up to fracture. Temperature dependence of the friction stress τF (T) and the interdislocation interaction parameter α(T) were also obtained. The change in the fraction of straight dislocations as a function of temperature was analyzed.

Phase Transformation Kinetics During Precipitation of an Ordered Intermetallic from a Disordered Matrix -a Computer Simulation

1990 ◽  
Vol 205 ◽  
Author(s):  
Long-Qing Chen ◽  
A.G. Khachaturyan
Keyword(s):  
Computer Simulation ◽  
Diffusion Theory ◽  
Antiphase Domain ◽  
Two Phase ◽  
Domain Boundaries ◽  
Ordered Intermetallic ◽  
Antiphase Domains ◽  
Ordering Transition ◽  
Kinetics Of ◽  
Ordered State

AbstractThe precipitation kinetics of an ordered intermetallic from a disordered matrix, which involves simultaneous ordering and decomposition, is studied by a computer simulation technique based on the microscopic diffusion theory. It is found that the precipitation starts from a congruent ordering transition, which may be continuous or nucleation and growth. This congruent ordering transition transforms the initially disordered state into a single phase nonstoichiometric ordered state with antiphase domains. The next stage is the decomposition which starts from the antiphase domain boundaries and then propagates into the ordered domains. And the final process is the coarsening of the order/disorder two-phase mixture. The predicted kinetics of precipitation is in excellent agreement with recent experimental observations in important alloy systems.

Physical and Mechanical Properties of Single Crystals of Co-Al-W Based Alloys with L12 Single-Phase and L12/fcc Two-Phase Microstructures

2008 ◽  
Vol 1128 ◽  
Author(s):  
Haruyuki Inui ◽  
Katsushi Tanaka ◽  
Kyosuke Kishida ◽  
Norihiko L. Okamoto ◽  
Takashi Oohashi
Keyword(s):  
Mechanical Properties ◽  
Single Crystal ◽  
Single Crystals ◽  
Yield Stress ◽  
Liquid Helium ◽  
Elastic Constants ◽  
Single Phase ◽  
Physical And Mechanical Properties ◽  
Helium Temperature ◽  
Two Phase

AbstractSingle-crystal elastic constants of Co3(Al,W) with the cubic L12 structure have been experimentally measured by resonance ultrasound spectroscopy at liquid helium temperature. The values of all the three independent single-crystal elastic constants and polycrystalline elastic constants of Co3(Al,W) experimentally determined are 15~25% larger than those of Ni3(Al,Ta) but are considerably smaller than those previously reported. Two-phase microstructures with cuboidal L12 precipitates being well aligned parallel to <100> and well faceted parallel to {100} are expected to form very easily in Co-base superalloys because of the large value of E111/E100 and cij of Co3(Al,W). This is indeed confirmed by experiment. Values of yield stress obtained for both [001] and [¯123] orientations of L12/fcc two-phase single crystals moderately decrease with the increase in temperature up to 800°C and then decrease rapidly with temperature above 800°C without any anomaly in yield stress. Slip on {111} is observed to occur for both orientations in the whole temperature range investigated.

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