The irradiation-induced rearrangements of solute atoms and point defects in structural materials take place on the nanometer (nm) length scale. In spite of significant degradation of the mechanical properties, these rearrangements are invisible even in high-resolution scanning electron microscopes. Cutting-edge technology is required to unravel how crystal defects evolve under irradiation.
The introduction of a high density of nm-scale defect sinks paves the way for the development of new irradiation-resistant materials. Nanostructured oxide-dispersion-strengthened steels and high-entropy alloys are promising candidate materials. The group takes part in related efforts. Ion irradiation is used to demonstrate (or disprove) favourable irradiation resistance.
Small-angle neutron scattering (SANS)
Nanodisperse chemical, structural and magnetic inhomogeneities scatter neutrons (n) or X-rays (X) at small angles. Information on nature, size, number and chemical composition of the inhomogeneities can be obtained from the angular dependence of the intensity of the scattered neutrons. The SANS experiments are performed at the Helmholtz-Zentrum Berlin, the neutron source FRM II at Munich, the Institute Laue-Langevin (ILL) at Grenoble, the Laboratoire Leon Brillouin at Saclay and at KFKI Budapest.
Transmission electron microscopy (TEM)
Irradiation-induced defects such as dislocation loops can be observed by TEM at nm-resolution. With respect to radiation damage, TEM and SANS represent complementary techniques. The application of TEM is also important for the characterization of size, concentration and composition of ODS particles.
Positron annihilation spectroscopy (PAS)
Positrons are self-searching, defect-specific probes for open-volume type defects of sub-nm size and in this respect supplementary to SANS and TEM. PAS experiments are performed in collaboration at the Institute of Radiation Physics.
While neutrons penetrate deeply into matter, energetic ions give rise to damage only in a µm-thin layer next to the surface. Methods suitable for damage characterization in thin layers include TEM, depth-resolved PAS and depth-sensing nanoindentation. Indentation hardness provides a link between irradiation-induced nanofeatures and mechanical property changes.