Flexural testing and modelling of tungsten by three-point bending for neutron and helium irradiation studies*

Fusion reactor divertor materials will be exposed to large thermal gradients caused by high heat fluxes. Tungsten materials in the divertor region must be able to withstand the induced thermal stresses with neutron and plasma particle interactions. The mechanical properties need to be investigated with small-scale disk specimen testing due to the low material-volume constrains in neutron irradiation testing environments. This study seeks to determine the stresses in tungsten under bending when it has been exposed to fission-based neutron irradiation and surface ion damage. The maximum stress in bending is located at the surface of the specimen, allowing to examine the surface under peak stresses. Modelling was performed to determine how these stresses accumulate on an unroughened surface compared to a surface that has an altered morphology from surface ion damage. Polycrystal and single crystal tungsten with orientation in the (110) plane at the disk surface were irradiated in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory and tested with three-point bend. The irradiations were performed in the removable beryllium layer of HFIR with a gadolinium thermal neutron shield to doses of 0.2-0.7 DPA in temperature zones of 430-670, 740-960, and 880-1090 C.