Brittle–ductile transitions in polycrystalline tungsten

Abstract

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.

Ductilisation of tungsten (W) through cold-rolling: R-curve behaviour

“…As a result, we will first show the fundamental ideas of the controlling mechanism of the BDT, mainly based on the work and model of Roberts et al In particular, most of our diagrams make use of Roberts's idea of the dislocation source position, that is that the dislocations are emitted from a source near the crack tip (see Roberts's suggestion [10]) and not from the crack tip (as suggested by Rice and Thomson [11]). This will be followed by the presentation of studies on the BDT in tungsten single crystals from Giannattasio and Roberts et al [12][13][14] and Gumbsch et al [15,16].…”

The mechanical properties of tungsten grown by chemical vapour deposition

“…The low value of E BDT found by Gumbsch et al can be attributed to the crystallography of the particular specimens used for their experiments in which, uniquely, the controlling process is likely to be the glide of edge dislocations. More recent work in Oxford has found E BDT to be approximately 1.0 eV in both pure polycrystalline and pure single-crystal tungsten [10] and 1.45 eV in less pure sintered material [11]. This implies that, for the general case, the BDT in tungsten is controlled by screw dislocation motion.…”

Surface morphology and deuterium retention in tungsten and tungsten–rhenium alloy exposed to low-energy, high flux D plasma

“…As this takes place, the D retention increases significantly [10]. Based on the temperature dependence of blister formation and D retention in recrystallized W exposed to low-energy, high flux D plasma with the same ion composition, ion energy and ion flux as used in this work [26], the BDT temperature for the plasma-exposed recrystallized W can be speculated to lie between 460 7 and 500 K. According to the strain rate dependence of the BDT temperature for recrystallized and polycrystalline W [24,27], the BDT temperatures for these materials are practically equal. Thus, it is believed that the brittle-to-ductile transition in the plasma-exposed warmrolled W occurs at a temperature between 460 and 500 K.…”