James Lennard

University Of Manchester

I recently completed my MSc in Nuclear Science and Technology at The University of Sheffield, during which I investigated tungsten thin-films for tokamak “armour” applications. I have a prior
background in materials science and worked as a metallurgist at AWE plc. for my industrial placement year. At The University of Manchester, I am working with Dr Enrique Jimenez-Melero
and Prof. Grace Burke on a project entitled ‘Plasticity and failure mechanisms in high-temperature ferritic steels produced by additive manufacturing’.

Additive manufacturing encompasses a range of environmentally-friendly processes which are allowing complex geometry designs to be realised which have previously been impossible through
traditional, ‘material-subtractive’ technologies. Moreover, intricate parts can be fabricated as single components; thereby eliminating the need to develop joining processes for bonding individual subcomponents. An additional opportunity to carefully control the chemistry of alloys can be achieved through powder selection and intimate blending of particles – this has recently been extended to the use of oxide-dispersion strengthened (ODS) steels, which are of interest for structural and plasmafacing tokamak applications due to their high radiation tolerances. Specifically, these steels offer potentially lucrative benefits for nuclear applications based on the grain-boundary pinning and dislocation-inhibiting qualities of nanoscale oxide particles distributed homogeneously throughout load-bearing components. Controlling these fundamental materials science mechanisms will prove key to engineering the mechanical properties of high-temperature ferritic steels which are typically plagued by low fracture toughnesses and strengths at temperatures approaching 1000 K. Finelydispersed oxide particles could further allow for alloying additions used in non-nuclear applications to be obviated more easily: including niobium and molybdenum, which will transmute readily to unacceptable radioisotopes in the ITER (and beyond) neutron environment.

ODS steel specimens manufactured by additive processing will be subjected to various loads and loading conditions at fusion-relevant temperatures in order to assess the effect of dispersed oxides
on key properties of ferritic steels such as creep resistance, tensile strength and fracture toughness. Principal to this work will be the use of synchrotron X-ray diffraction to monitor the in-situ
structural stability of these steels as thermomechanical testing proceeds, in addition to transmission electron microscopy for investigating deformation at the nanoscale.