Development of atomization gas and alloy composition for gas atomization reaction synthesis of oxide dispersion strengthened ferritic alloys

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2023-08
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Cockburn, Emma
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Anderson, Iver E
Pathak, Siddhartha
Peters, Frank
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Materials Science and Engineering
Abstract
As additive manufacturing techniques develop and unlock new potential for use in various industries, powder production needs to develop at the same rate. The future of nuclear power is dependent on the development of materials for ultrahigh temperature and/or high-flux radiation tolerant applications. Fe-based oxide dispersion strengthened (ODS) ferritic alloys are strong candidates for such applications. While mechanical alloying (MA) has been the traditional method of producing ODS alloys, gas atomization reaction synthesis (GARS) produces a cleaner feedstock of powders with Cr-enriched surface oxides and Y-containing intermetallics, creating oxide dispersoids during consolidation and heat treat, as in additive manufacturing processes. To understand the reaction between the intermetallic compounds and the oxygen reservoir in the GARS powders, scanning electron microscopy (SEM) and energy dispersive x-ray spectrometry (EDS) was completed to understand the distribution of oxygen within GARS powders of varying oxygen and elemental content. It was determined that the supposed crystalline surface oxide was not such, but rather an enhanced oxygenated zone (EOZ). The thickness of such EOZ was found to be dependent on the particle size, oxygen content in the atomization gas, and additions in the alloy composition. A linear relationship between EOZ thickness and powder diameter was found in powders produced with the atomization gas containing 1000ppm oxygen, and the addition of zirconium to the alloy was found to increase EOZ as well. Electromagnetic levitation (EML) experimentation was developed to allow for the investigation of the effect of oxygen concentration in the atomization gas. This required the development of a levitation coil capable of levitating the base alloy securely and controllably within a desired temperature range. Various iterations of coils were created and tested based on literature recommendations and empirical formulas. The EML system was adapted to support the chamber being pumped with various atomization gas compositions. To develop the EML process further, it is recommended that a bigger power source is used to allow for the levitation of alloys of interest.
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