Precipitate Stability and Helium Trapping in Advanced Steels

It is estimated that over 10,000 tons of steel will be used in the construction of a civilian fusion energy device. The continued safe operation and utility of a fusion energy device will, in part, rely on the structural integrity of the steel-manufactured components used within its design. These components could see unique operating conditions, including a damaging flux of high-energy neutrons that can alter their structure and chemistry. The neutron flux creates both atomic displacements and transmutation products such as helium in the steels. The aim of this research is to understand how various regimes of the neutron flux will impact the response of advanced steels with innovative nanometric precipitates additions formed intrinsically during manufacturing within its matrix. Specifically, the influence of the precipitate-matrix stability under a damaging energetic particle flux on the helium migration, coalescence, and trapping will be evaluated. The approach will use both ex situ and in situ dual beam ion irradiations to experimentally simulate the various neutron damage and transmutation conditions in a model advanced steel developed using computational thermodynamics and printed using additive manufacturing. Post irradiation, the changes in structure and chemistry will be assessed using an extensive characterization campaign using electron-microscopy based techniques. The experimental efforts will be coupled with advanced computer analysis algorithms and theoretical models to elucidate the underlying mechanisms that control precipitate stability and helium trapping in advanced steels. The work will provide the additional fundamental insights needed to further optimize the design and manufacturing of advanced steels for fusion energy systems.