In-situ formation of complex oxide precipitates during processing of oxide dispersion strengthened ferritic steels

• Use of dual drive planetary ball mill for Bench scale (>1 kg) production.
• X-ray diffraction and TEM were used to study transformations during sintering.
• HIPped and rolled samples with nearly 99% density successfully produced.

In fusion and fission reactor material development, ODS alloys are the most suitable candidate materials due to its high temperature creep properties and irradiation resistance properties. This paper describes the preparation of oxide dispersion strengthened alloy powder in large quantity (>1 kg batch) in dual drive planetary ball mill using pre-alloyed ferrtic steel powder with nano sized Y2O3. The consolidation of the powders was carried out in hot isostatic press (HIP) followed by hot rolling. 99% of the theoretical density was achieved by this method. The vickers hardness values of pressed and rolled samples were in the range of 380 ± 2HV and 719 ± 2HV, respectively. Samples were further investigated using X-ray diffraction particle size analyzer and electron microscope. Initial increase in particle size with milling was observed showing flattening of the particle. It was found that 5 h of milling time is sufficient to reduce the particle size to achieve the desired size. Transmission electron microscopy analysis of milled ODS steel powder revealed a uniform distribution of combustion synthesized nano-Y2O3 in ferritic steel matrix after a milling time of 5 h. Preliminary results demonstrated suitability of dual drive planetary ball mill for mass production of alloy within a short time due to various kinds of forces acting at a time during milling process. Fine monoclinic Y2Si2O7 precipitates were also observed in the steel. This study explains the particle characteristics of nano Y2O3 dispersed ODS powder and formation of nano clusters in ODS ferritic alloy.