Time: 10:30 a.m.
Place: ICAMS Seminar Room IC 02/718
Jens Reiser, KIT Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany
For tungsten (W), its tendency to fail at low temperatures by brittle fracture is a major limitation in its commercial exploitation. This raises the question of how to make tungsten ductile. Our ductilisation approach is the modification of the microstructure through cold-rolling. In this contribution I will present a study where we assess the evolution of the deformation and fracture mechanisms through cold-rolling.
A batch of tungsten (W) sheets with thicknesses of 1 mm, 0.5 mm, 0.3 mm, 0.2 mm, and 0.1 mm has been rolled out of a single sintered compact. The 0.1 mm tungsten foil possesses a grain size of 230 nm in the S-direction and has exceptional mechanical properties:
- Brittle-to-ductile transition: occurs at -90°C (183 K).
- Tensile properties at room temperature: no hardening, increase of total elongation
- Strain-rate sensitivity above Tc: it exists and it increases with temperature
Aim of this presentation is to discuss the role of cold-rolling induced lattice defects (e.g. vacancies, dislocation boundaries, HAGBs) and to address the following questions: What is the reason for the enhanced mobility of dislocations? Is the nucleation and migration of kinkpairs replaced by the phonon drag mechanism? What is the role of the vacancy mobility? May partial recrystallization (HAGBs loaded with dislocations start to move) contribute to this behaviour? And how can modelling contribute to solve these issues?