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.
KeywordsY2O3 HfO2 Oxide Dispersion Strengthened High Number Density Oxide Dispersion Strengthened Alloy
Research sponsored by the US Department of Energy (DOE), Office of Fusion Energy Sciences, Fusion Energy Materials Program. A portion of the microscopy was performed as part of a user proposal at ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility, and also some of the microscopy research was performed, in part, using instrumentation (FEI Talos F200X S/TEM) provided by the Department of Energy, Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science User Facilities. D. W. Coffey, T. M. Lowe, M. S. Stephens, and T. S. Geer assisted with the experimental work. D. Cullen and K. G. Field provided comments on the results and manuscript and S. Dryepondt provided PM2000.
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