A new model of the brittle-to-ductile transition based on a collective dislocation generation instability
- Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Materials Science and Engineering
A new model of the brittle-to-ductile (BDT) transition has been proposed based on a cooperative mechanism of dislocation generation. In the existing models, the BDT is assumed to be either controlled by the nucleation of a single dislocation or the mobility of a group of dislocations. The effects of temperature enter these models only via thermally activated generation or motion of dislocations. In contrast, the model advanced in this work suggests that the BDT corresponds to a combined thermal-and-stress induced cooperative instability of a large number of dislocation loops. The analysis is carried out in the framework of statistical mechanics and is closely related to the well-known Kosterlitz-Thouless type dislocation instability. The new model not only identifies the specific role of the crack tip in the BDT but also suggests that a sudden onset of plasticity at a certain temperature is possible in crack-free crystals. There is ample evidence in the literature for this. The authors have performed experiments to check the model, looking for the onset of sudden massive plasticity at the BDT. In order to minimize the uncertainties in the stress distribution, the experiments are performed on homogeneously stressed, nearly dislocation-free silicon. Results obtained on highly stressed Si/Ge epitaxial overlayers on silicon are very encouraging. The authors see a sudden onset of stress relaxation in the overlayer during heating in which the mobile dislocation density increases from near-zero to 10{sup 11} over a small temperature interval and corresponds to the onset of dislocation activity in the film, leading to the production of interfacial dislocations.
- OSTI ID:
- 293120
- Report Number(s):
- CONF-970980--; ISBN 0-87339-381-3
- Country of Publication:
- United States
- Language:
- English
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