Characterization of nano-sized particles in 14%Cr oxide dispersion strengthened (ODS) steel using classical and frontier microscopy methods

Oxide dispersion strengthened (ODS) steels exhibit superior mechanical properties and irradiation resistance due to nano-sized oxides, highly dispersed in the metallic matrix. The mechanical properties are affected by the structure, composition, size and density of the nano-sized oxides. Despite numerous reports on the characterization of these oxides, ambiguity regarding their composition, crystallographic structure and orientation relationship with the matrix remains. In the present study, characterization of the crystallographic structure of oxide particles existing in 14%Cr ODS steel was performed using classical and novel transmission electron microscopy (TEM) methods. 3D dispersion, density and composition of these oxides were evaluated by atom probe tomography (APT). Three populations of particles were detected: highly dispersed, 3–20 nm Fe(Cr,Ti,Y)O particles with spinel structure; 50–150 nm YTiO₃ and large (100–200 nm) particles identified as cubic TiC. The spinel-type particles displayed Bain and Kurdjumov-Sachs orientation relationships (OR) with the ferritic matrix. Applying electron diffraction tomography, the YTiO₃ structure was attributed to the GdFeO₃ (distorted perovskite)-type and its lattice parameters were refined as a = 5.46 Å, b = 7.66 Å and c = 5.28 Å. Orientation relationship of the YTiO₃ particles and Fe matrix were determined as [110]_Fe//[210]_oxide and (110)_Fe//(002)_oxide.