Six tungsten grades were irradiated in the Belgian material test reactor (BR2) and characterized by Vickers hardness tests in order to investigate the irradiation-induced hardening. These tungsten grades included: Plansee (Austria) ITER specification tungsten, ALMT (Japan) ITER specification tungsten, two products from KIT (Germany) produced by powder injection molding (PIM) and strengthened by 1% TiC and 2% Y2O3 dispersed particles, and rolled tungsten strengthened by 0.5% ZrC from ISSP (China). The materials were irradiated face-to-face at three temperatures equal to 600 °C, 1000 °C, and 1200 °C to the dose of ∼1 dpa. The Vickers hardness tests under 200 gf (HV0.2) were performed at room temperature. The Vickers hardness increases as the irradiation temperature increases from 600 to 1000 °C for all materials, except for the ZrC-reinforced tungsten, for which the increase of hardness does not depend on irradiation temperature. The irradiation-induced hardness decreases after irradiation at 1200 °C. This is a result of defect annealing enhanced by thermally activated diffusion. However, even at 1200 °C, the impact of neutron irradiation on the hardness increase remains significant; the hardness increases by ∼30 to 60% compared to the non-irradiated value. In the case of TiC-strengthened material, the irradiation hardening progressively raises with irradiation temperature, which cannot be explained by the accumulation of neutron irradiation defects solely.

A large campaign of characterization of the ductile to brittle transition temperature (DBTT) and microstructure has been performed on several commercial and lab-scale pure tungsten grades, potassium doped tungsten alloys, and particle reinforced tungsten grades (with particles of TiC, Y₂O₃, or ZrC), all integrated in a large-scale neutron irradiation campaign. The DBTT is deduced based on miniaturized three-point bending tests to provide reference data for the assessment of the irradiation effects on the tungsten alloys. This miniaturized geometry is designed to minimize the operational cost of neutron irradiation, to speed up post-irradiation examination, and to reduce the amount of nuclear waste. The resulting DBTT ranges from around −15 up to 450 °C, depending on the material. The potassium doped tungsten alloys have the lowest DBTT, followed by rolled ZrC reinforced tungsten grade, commercial pure tungsten grades, lab-scale pure tungsten grades, and other particle reinforced tungsten grades. The crack plane orientation and microstructure with respect to grain shape and grain boundaries significantly affect the DBTT for forged/rolled tungsten products with elongated grains. The L-T orientation has a lower DBTT compared to the T-L orientation. Moreover, the DBTT difference in the L-T and T-L orientation raises with increasing the grain aspect ratio. An attempt is made to establish a relationship between the density of low and high angle grain boundaries and DBTT value. The obtained relationship is discussed in the frame of mechanical processing (i.e., rolling or forging) to optimize the DBTT by optimized manufacturing. The results are compared to recent computational predictions of the DBTT in tungsten.