Steve Roberts

"An analytical method to extract irradiation hardening from nanoindentation hardness-depth curves" Anna Kareer, A. Prasitthipayong, David Krumwiede, D.M. Collins, Peter Hosemann, Steve Roberts, Journal of Nuclear Materials Vol. 498 2018 274-281 Link
"Dislocation loop evolution during in-situ ion irradiation of model FeCrAl alloys" Philip Edmondson, Kevin Field, Jack Haley, Steve Roberts, Kumar Sridharan, Samuel A. Briggs, Sergio Lozano-Perez, Acta Materialia Vol. 136 2017 390-401 Link
Model FeCrAl alloys of Fe-10%Cr-5%Al, Fe-12%Cr-4.5%Al, Fe-15%Cr-4%Al, and Fe-18%Cr-3%Al (in wt %) were irradiated with 1 MeV Kr++ ions in-situ with transmission electron microscopy to a dose of 2.5 displacements per atom (dpa) at 320 °C. In all cases, the microstructural damage consisted of dislocation loops with ½<111> and <100> Burgers vectors. The proportion of ½<111> dislocation loops varied from ~50% in the Fe-10%Cr-5%Al model alloy and the Fe-18Cr%-3%Al model alloy to a peak of ~80% in the model Fe-15%Cr-4.5%Al alloy. The dislocation loop volume density increased with dose for all alloys and showed signs of approaching an upper limit. The total loop populations at 2.5 dpa had a slight (and possibly insignificant) decline as the chromium content was increased from 10 to 15 wt %, but the Fe-18%Cr-3%Al alloy had a dislocation loop population ~50% smaller than the other model alloys. The largest dislocation loops in each alloy had image sizes of close to 20 nm in the micrographs, and the median diameters for all alloys ranged from 6 to 8 nm. Nature analysis by the inside-outside method indicated most dislocation loops were interstitial type.
"Mechanical properties and plasticity size effect of Fe-6%Cr irradiated by Fe ions and by neutrons" G. Robert Odette, Chris Hardie, Shavkat Akhmadaliev, Steve Roberts, Y Wu, Journal of Nuclear Materials Vol. 482 2016 236-247 Link
The mechanical behaviour of Fe6%Cr in the un-irradiated, self-ion irradiated and neutron irradiated conditions was measured and compared. Irradiations were performed to the same dose and at the same temperature but to very different damage rates for both methods. The materials were tested using nanoindentation and micromechanical testing, and compared with microstructural observations from Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT) reported elsewhere. Irradiated and un-irradiated micro-cantilevers with a wide range of dimensions were used to study the interrelationships between irradiation hardening and size effects in small-scale plasticity. TEM and APT results identified that the dislocation loop densities were ∼2.9 × 1022m−3 for the neutron irradiated material and only 1.4 × 1022m−3 for the ion irradiated material. Cr segregation to loops was only found for the neutron-irradiated material. The nanoindentation hardness increase due to neutron irradiation was 3 GPa and that due to ion irradiation 1 GPa. The differences between the effects of the two irradiation types are discussed, taking into account inconsistencies in damage calculations, and the differences in PKA spectra, dose rate and transmutation products for the two irradiation types.
"Microstructural examination of neutron, proton and self-ion irradiation damage in a model Fe9Cr alloy" Jack Haley, G. Robert Odette, Steve Roberts, Journal of Nuclear Materials Vol. 533 2020 Link
"Microstructural examination of neutron, proton and self-ion irradiation damage in a model Fe9Cr alloy" Jack Haley, S. de Moraes Shubeita, P. Wady, A.J. London, G. Robert Odette, S. Lozano, Steve Roberts, Journal of Nuclear Materials Vol. 533 2020 Link