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.

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.

Normal and Anomalous Yield Stresses in a Tial Single Crystal and the Dominating Dislocation Mechanisms.

1994 ◽  
Vol 364 ◽  
Author(s):  
N. Bird ◽  
G. Taylor ◽  
Y. Q. Sun
Keyword(s):  
Single Crystal ◽  
Yield Stress ◽  
Slip Plane ◽  
Cross Slip ◽  
Axial Orientation ◽  
Entire Temperature Range ◽  
Temperature Range

AbstractSingle crystal γ-TiAl with axial orientation [3 16 15] has been tested in compression between 4K and 1048K and the dislocation structures observed in TEM. The slip plane was found to be (111) over the entire temperature range tested. Three regimes exist in the variation of the yield stress with temperature, whereas the dislocation substructures are of two types, dominated by 30° 1/3[112] and 1/2 < 110] dislocations respectively. The anomalous yield stress is associated with 1/2 < 110] dislocations undergoing frequent cross-slip off the (111) plane.

scholarly journals Determination of the of Rate Cross Slip of Screw Dislocations

2000 ◽  
Vol 85 (18) ◽  
pp. 3866-3869 ◽  
Author(s):  
T. Vegge ◽  
T. Rasmussen ◽  
T. Leffers ◽  
O. B. Pedersen ◽  
K. W. Jacobsen
Keyword(s):  
Cross Slip ◽  
Screw Dislocations

Cross-Slip from Octahedral Onto Cube Planes in Ni3Al

1974 ◽  
Vol 32 ◽  
pp. 502-503
Author(s):  
J. M. Oblak ◽  
W. H. Rand
Keyword(s):  
Flow Stress ◽  
Boundary Energy ◽  
Antiphase Boundary ◽  
Cross Slip ◽  
Temperature Range ◽  
Slip Event

Slip in Ni3Al takes place primarily upon close-packed <111> planes by the motion of paired a/2 dislocations, although slip can also be initiated upon cube planes at temperatures above 700°K (1,2). Because the antiphase boundary energy is at a minimum on <001> (3), a net reduction of energy is possible if such paired dislocations cross-slip from octahedral onto cube planes. The likelihood of this cross-slip event plays an important role in the theories on the flow stress of Ni3Al (1,2). Observations reported previously (h) demonstrate that cross-slip takes place at 1030°K. This investigation represents a more thorough exploration of its temperature range of occurrence.

Dislocation Configurations in the γ’ Phase Ni3(AlTi)

1968 ◽  
Vol 26 ◽  
pp. 258-259
Author(s):  
P. H. Thornton ◽  
R. G. Davies
Keyword(s):  
Shear Stress ◽  
Slip Plane ◽  
Wide Temperature Range ◽  
Deformation Behavior ◽  
Slip Mode ◽  
Screw Dislocations ◽  
Temperature Range ◽  
Octahedral Slip ◽  
Critical Resolved Shear Stress

The γ’ phase Ni3Al, as with all f.c.c. metals and also the isomorphous phase CU3Au, deforms by octahedral slip over a wide temperature range. However, in contrast to these other materials cube slip can also occur in γ'. This extra slip mode, which is very unusual in metals, has been observed to operate at temperatures near 800°C. In the present study of the deformation behavior of the γ' phase Ni3(AlTi), the critical resolved shear stress for cube slip was found to become equal to that of octahedral slip at 400°C approximately and was less than that of octahedral slip at 700°C.An examination of slip plane sections of <100> oriented crystals of Ni3(AlTi), in which deformation is restricted to the ﹛111﹜ mode, revealed mainly screw dislocations in samples deformed at temperatures between 25°C and 750°C. At the lower temperatures, the screw dislocations were straight (Fig. 1) whereas at the higher temperatures the dislocations were more heavily jogged (Fig. 2). In contrast, slip plane sections taken from crystals which could deform by cube slip showed both edge and screw dislocations (Fig. 3).

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