rate dependence of the brittle-to-ductile transition temperature in tungsten. Philosophical Magazine, Taylor & Francis, 2008, 87 (17) AbstractWe have investigated the strain rate dependence of the brittle-to-ductile transition (BDT) temperature in pre-cracked tungsten single-crystals and polycrystals. There is an unambiguousArrhenius relationship over four decades of strain rate, giving an activation energy for the process controlling the BDT of 1.05 eV. This is equal to the activation energy for double-kink formation on screw dislocations, suggesting that their motion controls the brittle-ductile transition.

The strain rate dependence of the brittle-to-ductile transition (BDT) temperature was investigated in notched and un-notched miniature bars made of high-purity polycrystalline tungsten and in notched bars of less-pure sintered material. The activation energy, E BDT , for the process controlling the BDT in pure tungsten was equal to 1.0 eV both in un-notched and notched specimens, though the brittle-ductile transition temperature, T BDT , was % 40 K lower at each strain rate for the un-notched samples, indicating that the activation energy, E BDT , is a materials parameter, independent of geometrical factors. The experimental data obtained from pure tungsten are described well by a two-dimensional dislocation-dynamics model of crack-tip plasticity, which is also discussed. For sintered tungsten, E BDT was found to be 1.45 eV; T BDT at a given strain rate was higher than in the pure tungsten by % 90 K, suggesting that the BDT in tungsten is very sensitive to impurity levels.

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We describe a method to observe the directional emission of electromagnetic radiation produced by the radiative decay of surface plasmonpolaritons (SPPs) that allows the dispersion of the modes in k-space to be directly visualized. The method presented here opens up the possibility of characterizing the effect of a wide range of surface morphologies on SPP dispersion. As an example we show the formation of a stop-band for SPPs when the metal surface is modulated in the form of a diffraction grating.