Advanced nuclear reactors require cladding materials with high creep, corrosion and swelling resistance. Structural materials for core nuclear components have evolved continuously to increase the fuel performance. The first-generation material, austenitic stainless steel can withstand only up to 50 displacements per atom (dpa). For the doses above 50dpa, ferritic/martensitic steels are used. Ferritic/martensitic steels exhibit high swelling resistance than austenitic steels but their poor thermal creep strength at operating temperatures limits their usage. To overcome this problem, new emerging materials, namely, oxide dispersion strengthened (ODS) steels have been developed.

These ODS steels are processed mainly through powder metallurgy route. The properties of ODS steels primarily depends on microstructure, particularly the size and number density of clusters formed in these steels. The nature, type, amount of oxides and other alloying elements also affect the properties of these steels. Commonly used oxides for ODS steels are Y2O3, TiO2, ZrO2 and TaO2. Y2Ti2O7, Y2Zr2O7, Y2Hf2O7 have pyrochlore structure and are found to be promising dispersoids for steel-based oxide dispersed strengthened (ODS) alloys, which are used in nuclear reactor and supercritical boilers applications. These finely dispersed, nanometre sized particles restrict dislocation motion, thereby improving mechanical properties at high temperatures, while simultaneously generating a large number of particle-matrix interfaces, which act as a sink for radiation induced defects.

In this study, pyrochlores has been synthesized in two different ways. First, by direct synthesis of Y2Ti2O7, Y2Zr2O7 and Y2Hf2O7 through mechanically activated synthesis and reverse co-precipitation (RCP). The RCP technique could yield pyrochlore phase at lower temperatures with finer crystalline size. The structural analysis was done through X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectra to confirm the presence of single phase and nanocrystallinity of oxides. Raman spectra also probes into local disorderness in the structure and bond length. Y2Hf2O7 synthesised through MAA has the highest hardness (20 GPA) among all the oxides synthesised in the present study and those reported so far. Further, Y2Ti2O7 has higher Young’s modulus than the Y2Zr2O7, Y2Hf2O7 due to the orderness in the structure.

In the present work, we have also synthesized multicomponent pyrochlores (Y2(TiZrHfMoV)2O7) has been synthesised using reverse co-precipitation technique and the powder consolidation is done through spark plasma sintering (SPS). The cations were chosen based on the Paulings rule, where each cation has nearby ionic radii, stable oxidation state and favourable co-ordination number. The structural characterisations of powders and pellets are done through XRD analysis, Raman and TEM analysis. The composition was confirmed through the energy dispersive spectroscopy associated with SEM and X-ray photoelectron spectroscopic analysis (XPS). Differential Scanning Calorimetry (DSC) analysis was carried out to study the phase transitions. XPS and DSC results were correlated to understand the phase formation criteria in the HEP. The mechanical properties were measured through the nano indentation technique in the SPS pellets. The experimental results demonstrate that the HEP could be formed in the present study by calcination at the lowest reported temperature so far and was found to be stable up to 1000 ◦C. Among the HEPs, Y2(TiZrHfMo)2O7 has a hardness of about 20 GPa. Hence, synthesised oxides found to be potential dispersoid for ODS steels.