Effects of annealing temperature on nanoscale particles in oxide dispersion strengthened Fe-15Cr alloy powders with Ti and Zr additions

Oxide dispersion strengthened (ODS) Fe-15Cr ferritic alloy powders with Ti and Zr additions were fabricated by mechanical alloying (MA) and subsequent annealed from 900 to 1200 °C. The microstructure of annealed powders was characterized using transmission electron microscopy (TEM), elemental mapping and synchrotron small angle X-ray scattering (SAXS). The hardness of the powders annealed at different temperature was measured. TEM and SAXS results showed that very high density nanoscale oxides are formed in annealed powders. The size of nanoscale oxides increases slightly and the number density decreases with increasing annealing temperature. Energy-dispersive X-ray spectroscopy (EDS) mapping revealed that Y-Ti-Zr-rich nanoscale oxides are found in the powders annealed at 900 °C. It is worth to note that core/shell structure nanoscale oxides with Y-Zr-rich oxide cores and Ti-rich shells are temperature-dependent and formed at 1000 °C. However, at 1100 °C and higher annealing temperature, the Ti-rich shell vanishes and only Y-Zr-rich nanoscale oxides are observed. A new formation mechanism of core/shell structure nanoscale oxides is proposed in this study. With the increasing annealing temperature, the average grain size increases and the hardness decreases.