Novel consolidation methods of Fe-base oxide dispersion strengthened powders produced via gas-atomization reaction synthesis

Abstract

<p>Mechanically alloyed Fe-base oxide dispersion strengthened (ODS) alloys are strong candidates for application as drop-in accident tolerant fuel claddings for existing nuclear power plants and as structural materials in Generation IV nuclear power plants due to their retained high temperature strength and corrosion resistance, in addition to their resistance to void swelling and failure under radiative environments. Mechanically alloying (MA) processes for generating Fe-ODS materials require long (40+h) high energy milling times, and the resulting powders may vary in composition from batch to batch due to contamination from milling materials. Gas atomized reaction synthesized (GARS) Fe-ODS precursor powder production offers an alternative higher efficiency method of producing Fe-ODS materials, but so far have only been consolidated via hot isostatic pressing. Novel application of vacuum hot pressing and cold spray deposition are investigated as alternative methods for consolidation of GARS Fe-ODS precursor powders.</p> <p>Vacuum hot pressing compared the as-pressed microstructures of Al containing GARS Fe ODS precursor powder CR-200 to the non-Al containing CR-204. The powders were pressed under 100MPa load for 4h at 850°C. The as-pressed compacts were not fully sintered and had ~90% density in the as-pressed state. Heat treatment at 1100 and 1200°C for 2.5h and at 1200°C for 12h resulted in development of coarsened IMCs and limited oxide phases primarily located along PPBs. It was determined that both powders show insufficient oxygen content ratios to develop the desired concentration of nano-metric oxide dispersoids. Also, it was determined that before heat treating to initiate the oxygen exchange reaction, VHP samples will need to be further deformed to break up PPBs and introduce greater dislocation densities as nucleation sites for the dispersoid phase.</p> <p>Cold spray deposition (CS) of CR-200 resulted in generation of a flat test coupon that was sectioned and evaluated. The as-deposited sample had an average of 93% density. Differential scanning calorimetry was used to confirm the presence of stored energy due to plastic deformation from the deposition without the use of transition electron microscopy (TEM) techniques. If CS-deposition is explored in the future for consolidation of these powders, it is recommended that a higher temperature or higher velocity accelerating gas be used for the deposition to promote complete cold welding of the powder particles and resulting higher as-deposited density.</p>