Advanced TEM characterization of oxide nanoparticles in ODS Fe 12Cr 5Al alloys
The oxide nanoparticles present in three oxide dispersion strengthened (ODS) Fe 12Cr 5Al alloys containing additions of (1) Y2O3 (125Y) (2) Y2O3 ZrO2 (125YZ) and (3) Y2O3 HfO2 (125YH) were investigated using transmission and scanning transmission electron microscopy. In all three alloys nano sized <3.5 nm) oxide particles distributed uniformly throughout the microstructure were characterized using advanced electron microscopy techniques. In the 125Y alloy, mainly Al2O3 and yttrium aluminum garnet (YAG) phases (Y3Al5O12) were present, while in the 125YZ alloy, additional Zr(C,N) precipitates were identified. The 125YH alloy had the most complex precipitation sequence whereby in addition to the YAG and Al2O3 phases, Hf(C,N) Y2Hf2O7, and HfO2 precipitates were also found. The presence of HfO2 was mainly due to the incomplete incorporation of HfO2 powder during mechanical alloying of the 125YH alloy. The alloy having the highest total number density of the oxides, the smallest grain size, and the highest Vickers hardness was the 125YZ alloy indicating, that Y2O3 ZrO2 additions had the strongest effect on grain size and tensile properties. High temperature mechanical testing will be addressed in the near future, while irradiation studies are underway to investigate the irradiation resistance of these new ODS FeCrAl alloys.
Journal of Materials Science