Mechanical Engineering Seminar: Dr. Celine Hin
Nanostructured Ferritic Alloys as Future Materials for Fusion Reactor
Capitalizing on rising energy prices, growing concern about global warming, interest in reducing reliance on fossil fuels, and a favourable political climate, the nuclear industry is working to achieve a renaissance around the world. Worldwide interests particularly focus on fusion reactor systems. Advanced fusion energy systems require the development of materials able to resist to high operating temperatures, high neutron exposure levels, and high thermo-mechanical stresses. In addition, the transmutation products generated in structural materials by the high energy neutrons produced in the deuterium-tritiumplasma in nuclear reactors can also drastically change the microstructure evolution in these structural materials, and consequently their mechanical behaviours.
Many efforts have been deployed to develop irradiation-damage-resistant alloys. Certain features, which can improve irradiation-damage resistance have been identified such as (a) a high, stable dislocation sink strength, and a high number density of nanometer scale precipitates which act as trap sites for He bubbles to avoid their swelling and to protect grain boundaries against embrittlement, and (b) fine grain size and high dislocation densities to ensure high creep strength to allow their operation at temperatures above the atom displacement regime. Some of these features have been observed in nanostructured ferritic alloys such as MA957 and MA956.
Prior works on this topic show that a high-number density of nanoscale Y-Ti-O clusters can improve creep resistance. It is also believed that the Y-Ti-O clusters, in addition to impeding dislocations and reducing grain-boundary mobility, act as traps for insoluble helium that would be generated in fusion reactor structural components. However, many questions exist related to the formation, structure and thermal stability of these Y-Ti-O nanoparticles that affect the optimal processing method and their performance in extreme environments. For example, it is necessary to understand their kinetic pathway of precipitation during an anisothermal heat treatment in order to develop improved processing methods and fully understand their atomic-scale structure and composition. Kinetic Monte Carlo techniques provide the ability to understand the kinetic paths controlling the precipitation of nanoclusters at the atomistic scale.
In our study, we provide insight into how oxides nanoclusters form in Fe-Ti-O and Fe-Y-O ternary alloys, shedding light on the complex kinetic pathway to precipitation in Fe-Y-Ti-O quaternary alloys. Then, we make the link between the microstructure evolution and the mechanical properties. We will conclude by highlighting a number of ongoing problems relative to the improvement of nanostructured ferritic alloys.
Celine Hin did her Ph.D. at the Commissariat a l’Energie Atomique at Saclay where she worked on the understanding of heterogeneous precipitation in ferritic alloys. Then, she spent one year at UC Berkeley in the nuclear engineering department where she studied the link between the microstructure evolution and the mechanical properties in nanostructured ferritic alloys. In 2007, she joined the Carter’s group at MIT in the department of Materials Science and Engineering, where her research on the Li-ion batteries focused on developing a Grand Canonical Kinetic Monte Carlo algorithm to study the influence of particle orientations in the electrolyte on the cell voltage at atomic scale. Finally, she joined the Department of Mechanical Engineering at MIT in 2009, where she is working on thermoelectric materials, trying to improve the figure of merit in PbTe systems using DFT calculations.