In order to increase efficiency and sustainability of a nuclear fusion reactor, structural materials will have to face higher temperatures and higher neutron doses. Therefore, new materials need to be developed or current structural materials need to be adapted for more severe operating conditions.
This PhD project, as part of the international fusion research programme, aims to improve performance of reduced activation ferritic/martensitic (RAFM) steels by generating and applying metallurgical knowledge through dedicated thermo-chemical-mechanical treatment (TMT) to obtain the required microstructure and mechanical properties.
In 2014-2018, advanced TMT processing routes were investigated to produce new heats with improved mechanical properties (lower ductile to brittle transition temperature, higher creep resistance). Different strategies were applied to achieve: i) different normalization (austenite formation), ii) varied tempering (carbo-nitride formation), iii) thermo-mechanical treatment (so-called ausforming) and iv) composition variation (C, N, W, Ta, V). By varying these parameters independently, the single-variable impact was assessed.
The goal of this project is to utilize the conclusions made earlier and further optimize the fabrication procedures using a multi-variable approach. Both the normalization and tempering treatment schedule will be alternated based on the lessons learned from the single-variable assessment. By using the high throughput innovative equipment available at OCAS, multiple heat treatments can be investigated in parallel, thus allowing to screen many different parameters.
The main objective of the thesis is the optimization of mechanical properties by thermo-mechanical treatment (in terms of normalization/tempering temperature, time and cooling/deformation rate) to achieve initially low ductile to brittle transition temperature (DBTT) and reduced shift of DBTT under neutron irradiation of:
- Selected composition provided by thermo-dynamical modelling, as assessed in the previous project
- Clean steels to avoid the formation of irradiation induced solute-rich-clusters
- Standard Eurofer steel
Finally, the most promising candidates will be subjected to neutron-irradiation in BR-2.