The thermal stability of non-stoichiometric Y-Zr-O nanoparticles in oxide dispersion strengthened (ODS) Mo alloys

In our previous work, a nanostructured oxide dispersion strengthened (ODS) Mo alloy with a high density of non-stoichiometric Y-Zr-O nanoparticles was developed as fuel cladding material. Considering the hostile high-temperature condition, this study focuses on the thermal stability of non-stoichiometric Y-Zr-O nanoparticles at 1400 °C for 48 h. Results showed that non-stoichiometric Y-Zr-O nanoparticles appeared to coarsen, resulting in the loss of coherency with the Mo matrix. The core/shell structure with Y-rich Y-Zr-O oxide cores and Zr-rich shells was formed by Zr diffusion from the Mo matrix to the oxides/matrix interface. Together with Ostwald ripening, it contributed to the evolution from metastable non-stoichiometric Y-Zr-O oxides to equilibrium Y-Zr-O oxides with a partitioned Y₂O₃ concentration distribution. Further, the Zr addition accelerated the coarsening of Y-Zr-O oxides. Zr-rich Y-Zr-O oxides were more likely to coarsen due to the larger equilibrium solubility of the Zr element and diffusion activation energy than those of Y-rich Y-Zr-O oxides.