Positron annihilation characterization of nanostructured ferritic alloys

Nanostructured ferritic alloys (NFAs) were produced by mechanically alloying Fe–14Cr–3W–0.4Ti and 0.25Y2O3 (wt%) powders followed by hot isostatic pressing consolidation at 850, 1000 and 1150 °C. Positron annihilation lifetime and orbital momentum spectroscopy measurements are in qualitative agreement with small angle neutron scattering, transmission electron microscopy and atom probe tomography observations, indicating that up to 50% of the annihilations occur at high densities of Y–Ti–O enriched nm-scale features (NFs). Some annihilations may also occur in small cavities. In Y-free control alloys, that do not contain NFs, positrons primarily annihilate in the Fe–Cr matrix and at features such as dislocations, while a small fraction annihilate in large cavities or Ar bubbles.