CHARACTERIZATION OF NANOSIZED OXIDES IN THE 14%Cr OXIDE DISPERSION STRENGTHENED STEEL

Oxide dispersion strengthened (ODS) steels are promising candidates for cladding tubes` materials in the next generation nuclear power plants. The reinforcement of highly dispersed oxide nanoparticles throughout the matrix, provides ODS steels with exceptional strength and creep resistance at high temperatures. The addition of Ti to these alloys reduces the particle size, leading to higher dispersion of fine Y-Ti-oxide particles. These oxides block mobile dislocations, resulting in increased hardness and strength. The most common types of such oxides which were reported to exist in these steels are Y₂Ti₂O₇ and Y₂TiO₅. However, most common diffraction patterns shown in the literature for these structures can also be indexed in terms of Y₂O₃, thus ambiguity regarding the nature of these oxide structures remains. Since structure and properties of materials are intimately linked, in depth characterization is crucial for understanding of physical properties. In the present study, detailed transmission electron microscopy (TEM) analysis, including high angular annular dark field (HAADF), energy filtered TEM (EFTEM) and electron energy loss spectroscopy (EELS), was conducted in order to determine the distribution, composition of oxide particles in a 14wt% Cr ODS alloy. It was found that oxides are composed mainly of Y, Ti and O. However, diffraction patterns obtained from several particles could not been indexed in terms of the Y₂Ti₂O₇ or Y₂TiO₅ structures. Electron diffraction tomography data set obtained from one particle was successfully indexed in terms of YTiO₃ (distorted perovskite derivative), which is rarely reported in the literature regarding these steels.