Shape Transformations of Ge Precipitates in Al

1991 ◽  
Vol 238 ◽  
Author(s):  
P. Lours ◽  
K. H. Westmacott ◽  
U. Dahmen
Keyword(s):  
Electron Microscope ◽  
Orientation Relationship ◽  
High Voltage ◽  
Temperature Cycling ◽  
Shape Transformation ◽  
Cube Orientation ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
Interface Roughening

ABSTRACTGe precipitates in Al-Ge alloys have been observed to undergo a transformation in shape during in-situ temperature cycling in a high voltage electron microscope. Octahedral precipitates with a parallel-cube orientation relationship spheroidized on heating and refaceted to the octahedral shape on cooling. This shape transformation was essentially conservative if the temperature excursions were kept small. These observations are discussed in terms of an interface roughening transformation.

In-situ electrical-resistivity measurements in the high-voltage electron microscope

1978 ◽  
Vol 36 (1) ◽  
pp. 68-69
Author(s):  
W. E. King
Keyword(s):  
Electrical Resistivity ◽  
Electron Microscope ◽  
High Voltage ◽  
Resistivity Measurements ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
High Voltage Electron ◽  
Wide Range ◽  
Helium Gas

A side-entry type, helium-temperature specimen stage that has the capability of in-situ electrical-resistivity measurements has been designed and developed for use in the AEI-EM7 1200-kV electron microscope at Argonne National Laboratory. The electrical-resistivity measurements complement the high-voltage electron microscope (HVEM) to yield a unique opportunity to investigate defect production in metals by electron irradiation over a wide range of defect concentrations.A flow cryostat that uses helium gas as a coolant is employed to attain and maintain any specified temperature between 10 and 300 K. The helium gas coolant eliminates the vibrations that arise from boiling liquid helium and the temperature instabilities due to alternating heat-transfer mechanisms in the two-phase temperature regime (4.215 K). Figure 1 shows a schematic view of the liquid/gaseous helium transfer system. A liquid-gas mixture can be used for fast cooldown. The cold tip of the transfer tube is inserted coincident with the tilt axis of the specimen stage, and the end of the coolant flow tube is positioned without contact within the heat exchanger of the copper specimen block (Fig. 2).

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.

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