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2 2001

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Diffusion processes in the dislocation cores during the high-temperature deformation of intermetallic alloys.

Messerschmidt U., Guder S., Häussler D., Bartsch M.

Inżynieria Materiałowa

2001

R. XXII, nr 5

627-632

In situ straining experiments in a high-voltage electron microscope to study dislocation dynamics and macroscopic deformation experiments including stress relaxation tests have been performed on a number of intermetallic alloys. There are many similarities in the dynamic behaviour of dislocations in the studied materials. In the low-temperature range, different mechanisms lead to a normal decrease of the flow stress with increasing temperature. At high temperatures, in several materials the dislocations move either in an unstable or a viscous way. They are then smoothly curved, or they are straight and oriented along crystallographic directions. As the low-temperature mechanisms cease at high temperatures, the viscous motion should be due to an additional friction mechanism which also causes the flow stress anomaly in the respective materials. It is suggested here that this mechanism involves diffusion processes in the dislocation cores, which can be described by the theory of the Cottrell effect. The diffusing species can be quite different, alloying components or intrinsic point defects like vacancies and antisite defects existing in the lattice or only in the dislocation cores. If the dislocations are straight and crystallographically oriented during their motion, they may be dissociated and move by a succession of glide and conservative climb between the partial dislocations. All these processes lead to an inverse dependence of the strain rate sensivity on the stress.

Observations of electromagnetic radiation in the Central Apennines seismic region

Ernst T., Jankowski J., Teisseyre R., Meloni A., Palangio P.

Acta Geophysica Polonica

2001

Vol. 49, nr 1

43-53

In recent years, continuous radio-noise recording is in use at many geophysical observatories, in order to detect possible earthquake precursors and/or coseismic signals. The recordings obtained indicate that electromagnetic radiation (e.g., in the range of 10-40 kH) can indeed be treated as seismic precursor. We present here the examples of successful prediction observation, which we have obtained in the Central Apennines region at the l'Aquila Observatory (Polish-Italian cooperation). A short discussion on relation between the evolution of stresses (dislocation dynamics) and electromagnetic emission supplements this paper.