Ductilisation of tungsten (W) through cold rolling: Change of brittle to ductile transition temperature (BDTT) in high deformed WThursday (29.09.2016) 15:30 - 15:45 Part of:
Tungsten is the designated material for plasma facing components of the ITER fusion device, caused e.g. by its high melting point, temperature strength and thermal conductivity . However, W as structure material is limited by its brittle fracture behaviour at ambient and elevated temperatures up to +450 °C . REISER et al.  showed that a grain size reduction through cold rolling decreases BDTT and hence improve fracture toughness.
In this study the BDTT-shift of W affected through cold rolling was investigated in detail by thoroughly designed and executed experiments. Fracture toughness test were performed with samples made of pure W sheets with increasing degree of deformation up to phi=3 and identical chemical composition. BDTTs of different microstructures were detected by secant method specified in ASTM E399. The influence of the applied stress state on BDTT was also evaluated. Activation energies of the BDT were calculated through the equation suggested by HARTMEIER et al.  subsequently.
Activation energies determined for all investigated material thicknesses point to the responsible BDTT controlling mechanisms in high deformed W-sheets. It was shown that BDTT is strongly affected by grain size and hence by the applied degree of deformation. The W-sheet underwent highest thickness reduction exhibit a BDTT of -70 °C. Compared to BDTT at +450 °C found by RIETH et al.  it is a tremendous improvement and furthermore an important success on the road to a safe structural application of W.
 RIETH, M.; BOUTARD, J.L.; DUDAREV, S.L. et al.: Review on the EFDA programme on tungsten materials technology and science. In: Journal of Nuclear Materials 417 (2011), 463–467
 RIETH, M.; HOFFMANN, A.: Influence of microstructure and notch fabrication on impact bending properties of tungsten materials. In: Int. Journal of Refractory Metals and Hard Materials 28 (2010), 679–686
 REISER, J.; HOFFMANN, J.; JÄNTSCH, U. et al.: Ductilisation of tungsten (W): On the shift of the brittle-to-ductile transition (BDT) to lower temperatures through cold rolling. In: Int. Journal of Refractory Metals and Hard Materials 54 (2016), 351–369
 HARTMEIER, A.; GUMBSCH, P.: On the Activation Energy for the Brittle/Ductile Transition. In: Rapid Research Notes phys. stat. sol. (b) 202 (1997), R1-R2
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