Dislocation Motion in λ Tial Studied by in situ Straining Experiments in the Hvem

1994 ◽  
Vol 364 ◽  
Author(s):  
Ulrich Messerschmidt ◽  
Martin Bartsch ◽  
Dietrich Häussler ◽  
Mark Aindow ◽  
Rainer Hattenhauer ◽  
...  
Keyword(s):  
Room Temperature ◽  
Precipitation Hardening ◽  
Dislocation Motion ◽  
Coarse Grained ◽  
Orientation Factor ◽  
Slip Mechanism ◽  
Voltage Electron ◽  
Slip Bands ◽  
Kinematic Behaviour

AbstractMicro-tensile specimens of coarse-grained Ti52at%Al crystals have been deformed in situ in a high voltage electron microscope at room temperature. In addition to some twinning, “simple” 1/2〈110] dislocations as well as superdislocations were moving, with the simple dislocations prevailing even if their orientation factor is lower than that of the superdislocations. Both types of dislocations are pinned, probably by small precipitates having a distance along the dislocations of about 100 nm. The precipitates consist most probably of Al2O3. Under stress, the dislocations bow out between the obstacles. The bowing is stronger for 1/2〈110] dislocations. An effective stress of about 41 MPa is estimated from their curvature. The kinematic behaviour of the dislocations is in accord with precipitation hardening. The dislocations are generated by the double-cross slip mechanism. Their density within the slip bands corresponds to a long-range internal stress of about 40 MPa. These data are consistent with the flow stress of PST crystals in the easy orientation, taken from the literature.

Dislocation Dynamics in Icosahedral Al-Pd-Mn Single Quasicrystals

2000 ◽  
Vol 643 ◽  
Author(s):  
Ulrich Messerschmidt ◽  
Martin Bartsch ◽  
Bert Geyer ◽  
Lars Ledig ◽  
Michael Feuerbacher ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Stress Exponent ◽  
High Voltage ◽  
Dislocation Dynamics ◽  
Slip Mechanism ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
Slip Planes ◽  
Slip Traces

AbstractThe paper reviews results from in situ straining experiments on Al-Pd-Mn single quasicrystals in a high-voltage electron microscope. Slip planes were determined from the orientation and width of slip traces. Dislocations are generated by a specific cross slip mechanism. On some slip traces, dislocations move at two distinctly different velocities. A stress exponent was determined on a single dislocation by observing its displacement under decreasing load. The in situexperiments reveal the behaviour of individual dislocations in a temperature range where the deformation of bulk specimens is strongly affected by recovery.

In-Situ Tem Investigation During Thermal Cycling of thin Copper Films

1996 ◽  
Vol 436 ◽  
Author(s):  
R.-M. Keller ◽  
W. Sigle ◽  
S. P. Baker ◽  
O. Kraft ◽  
E. Arzt
Keyword(s):  
Grain Growth ◽  
Room Temperature ◽  
Dislocation Motion ◽  
In Situ Tem ◽  
Copper Films ◽  
Stress Evolution ◽  
Cu Films ◽  
Transmission Electron ◽  
Insight Into

AbstractIn-situ transmission electron microscopy (TEM) was performed to study grain growth and dislocation motion during temperature cycles of Cu films with and without a cap layer. In addition, the substrate curvature method was employed to determine the corresponding stresstemperature curves from room temperature up to 600°C. The results of the in-situ TEM investigations provide insight into the microstructural evolution which occurs during the stress measurements. Grain growth occurred continuously throughout the first heating cycle in both cases. The evolution of dislocation structure observed in TEM supports an explanation of the stress evolution in both capped and uncapped films in terms of dislocation effects.

scholarly journals Nanoindentation-Induced Pile-Up in the Residual Impression of Crystalline Cu with Different Grain Size

2017 ◽  
Author(s):  
Jiangjiang Hu ◽  
Weiming Sun ◽  
Taihua Zhang ◽  
Yusheng Zhang
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Room Temperature ◽  
Indentation Depth ◽  
Dislocation Motion ◽  
Coarse Grained ◽  
Ultrafine Grained ◽  
Pile Up ◽  
Different Grain Size ◽  
Multiple Slips

At room temperature, the indentation morphologies of crystalline copper with different grain size including nanocrystalline (NC), ultrafine-grained (UFG) and coarse-grained (CG) copper were studied by nanoindentation at the strain rate of 0.04/s without holding time at indentation depth of 2000 nm. As the grain size increasing, the height of the pile-up around the residual indentation increases and then has a slightly decrease in the CG Cu, While the area of the pile-up increases constantly. Our analysis has revealed that the dislocation motion and GB activities in the NC Cu, some cross- and multiple-slips dislocation insides the larger grain in the UFG Cu, and forest dislocations from the intragranular Frank-Read sources in the CG Cu, would directly induce these distinct pile-up effect.

scholarly journals Synthesis, Characterization and Mechanical Properties of Nanocrystalline NiAl

1996 ◽  
Vol 457 ◽  
Author(s):  
M. S. Choudry ◽  
J. A. Eastman ◽  
R. J. DiMelfi ◽  
M. Dollar
Keyword(s):  
Room Temperature ◽  
Dark Field ◽  
Inert Gas ◽  
Coarse Grained ◽  
Gas Condensation ◽  
Grain Sizes ◽  
Room Temperature Ductility ◽  
Cast Alloys ◽  
Bend Tests

ABSTRACTNanocrystalline NiAl has been produced from pre-cast alloys using an electron beam inert gas condensation system. In-situ compaction was carried out at 100 to 300°C under vacuum conditions. Energy dispersive spectroscopy was used to determine chemical composition and homogeneity. Average grain sizes in the range of 4 to 10 nm were found from TEM dark field analyses. A compression-cage fixture was designed to perform disk bend tests. These tests revealed substantial room temperature ductility in nanocrystalline NiAl, while coarse grained NiAl showed no measurable room temperature ductility.

Combined In Situ Neutron Diffraction and Acoustic Emission of Twin Nucleation & Twin Growth in Extruded ZM20 Mg Alloy

2010 ◽  
Vol 652 ◽  
pp. 149-154 ◽  
Author(s):  
Ondrej Muránsky ◽  
Matthew R. Barnett ◽  
David G. Carr ◽  
Sven C. Vogel ◽  
E.C. Oliver
Keyword(s):  
Acoustic Emission ◽  
Neutron Diffraction ◽  
Room Temperature ◽  
Coarse Grained ◽  
Fine Grained ◽  
Grain Sizes ◽  
Twin Nucleation ◽  
Twin Growth ◽  
In Situ Neutron Diffraction

In the present work in situ neutron diffraction and acoustic emission were used concurrently to study deformation twinning in two ZM20 Mg alloys with significantly different grain sizes at room temperature. The combination of these techniques allows differentionation between the twin nucleation and the twin growth mechanisms. It is shown, that yielding and immediate post-yielding plasticity in compression is governed primarily by twin nucleation, whereas the plasticity at higher strains is governed by twin growth. The current results further suggest that yielding by twinning happens in a slightly different manner in the fine-grained as compared to the coarse-grained alloy.

In Situ HVEM Deformation of Aluminum Alloys

1980 ◽  
Vol 38 ◽  
pp. 28-29
Author(s):  
E. A. Kenik ◽  
R. W. Carpenter
Keyword(s):  
Solid Solution ◽  
Aluminum Alloy ◽  
Aluminum Alloys ◽  
Room Temperature ◽  
Tensile Deformation ◽  
Ductile Failure ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
Deformation Processes

Deformation processes in a series of aluminum alloys have been investigated by in situ tensile deformation in the ORNL high voltage electron microscope (HVEM). Both solid-solution-hardened and preoipitation-hardened alloys have been studied in several heat treatments. Interactions of moving dislocations with other dislocations, precipitates, grain boundaries, and other defects were investigated, as were the microstructural processes involved in the ductile failure of such specimens. Specimens of Al-4 wt % Cu and 1100 aluminum alloy were deformed at room temperature in a Gatan tensile deformation stage.

Defect Aggregation and Disordering in Electron Irradiated NiAl

1980 ◽  
Vol 38 ◽  
pp. 26-27
Author(s):  
H. C. Liu
Keyword(s):  
High Voltage ◽  
Room Temperature ◽  
Transformation Mechanism ◽  
Voltage Electron ◽  
High Voltage Electron ◽  
Defect Aggregation

Stoichiometric NiAl, which is an ordered B2 superlattice alloy, has been electron irradiated and observed in-situ in a Hitachi HU-650B high voltage electron micriscope from room temperature to 450°C. The purpose of this study is to understand the mobilities and clustering of interstitials and vacancies, and to investigate order-disorder transformation mechanism.

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