Speaker
David Armstrong
(Department of Materials, Oxford University, Oxford, United Kingdom)
Description
Tungsten is the leading candidate material for plasma facing applications in future tokamak systems, due to its high melting point, good sputtering resistance and low activity after irradiation. Despite this there has been a significant lack of study of the effect of transmutation products on the post irradiation mechanical behaviour of tungsten-based alloy systems. This will be key to understanding component lifetimes in future devices.
This study examines the formation of solute clusters and the associated hardening in W-2 at.%Re, W-2 at.%Ta, W-1 at.%Re-1 at.%Os and W-1 at.%Re-1 at.%Ta alloys induced by 2 MeV W+ ion irradiation at 573 and 773 K to damage levels of 33 dpa. Such clusters are known precursors to the formation of embrittling precipitates, which are likely to be the life-limiting factor in the operation of fusion reactor components. Due to the shallow depth of the damage layers, atom probe tomography was used to study chemical segregation and nanoindentation was used to measure increases in hardness due to irradiation.
The presence of osmium significantly increased post-irradiation hardening compared to rhenium-and tantalum-containing binary alloys (a peak hardness of 12 GPa, compared to 9 GPa for the binary alloys). Atom probe tomography analysis revealed solute clustering in rhenium- and osmium-containing alloys, with the size and number densities strongly dependent on alloy composition and irradiation temperature. The highest cluster number density was found in the ternary tungsten-rhenium-osmium alloy irradiated at 773 K. In this ternary alloy, osmium was found to cluster preferentially compared to rhenium. No clustering of tantalum atoms was seen in binary or ternary alloys. The implications of these results for the structural integrity of fusion reactor components will be discussed, and future research questions regarding phase stability in these systems will be identified.
Co-authors
Alan Xu
(Department of Materials, Oxford University, Oxford, United Kingdom)
Christian Beck
(Department of Materials, Oxford University, Oxford, United Kingdom)
David Armstrong
(Department of Materials, Oxford University, Oxford, United Kingdom)
George Smith
(Department of Materials, Oxford University, Oxford, United Kingdom)
Michael Moody
(Department of Materials, Oxford University, Oxford, United Kingdom)
Paul Bagot
(Department of Materials, Oxford University, Oxford, United Kingdom)
Steve Roberts
(Department of Materials, Oxford University, Oxford, United Kingdom)
