Development of a Novel Melt Spinning-Based Processing Route for Oxide Dispersion-Strengthened Steels
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INTRODUCTION
FERRITIC oxide dispersion-strengthened (ODS) steels that contain a high number density but low volume fraction of evenly distributed Y-, Ti-, and O-enriched nano-sized precipitates have emerged as one of the most promising structural material candidates for Generation IV fission and future fusion power plant concepts.[1–5] The widely practiced processing route for these ODS steels is essentially a two-step powder metallurgy process, consisting of mechanical alloying (MA) of 10- to 90-lm-diameter pre-alloyed Fe-based alloy powder together with a normally nano-sized (20 to 50 nm) Y2O3 powder until fine-scale mixing/alloying is achieved, followed by consolidation of the powder into a bulk form typically by hot isostatic pressing (HIP) or related technique.[5–10] This MA approach is now well optimized and convenient for laboratory-based studies, providing good quality material sufficient for detailed
ZULIANG HONG, ALASDAIR P.C. MORRISON, STEVE G. ROBERTS, and PATRICK S. GRANT are with Department of Materials, University of Oxford, Oxford, OX1 3PH, UK. Contact e-mail: [email protected] HONGTAO ZHANG is with the Department of Materials, Loughborough University, Leicestershire, LE11 3TU, UK. Manuscript submitted April 24, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
microscopy, irradiation, and mechanical property assessment. However, in technological terms, disadvantages of the MA route include prolonged processing time, small batch size, tendency for contamination associated with the high specific area of the powder, and the high inherent cost of the pre-alloyed feedstock powders, which combine to restrict wider commercial implementation of the MA-based route.[1,11–16] Thus, while key properties of ODS alloys, such as creep and irradiation resistance, are attractive, it is worthwhile to continue to explore alternative fabrication routes to replace/circumvent the MA process that might potentially achieve a higher throughput more suited for industrial production, probably with some, but acceptable, compromises in microstructure and mechanical properties. Recent efforts in this direction include in situ oxidation of a Y-containing melt during gas atomization, oxidation of a gas atomized Y-containing powder, and spray forming of a Y-containing melt.[17] While providing some encouragement, so far none of these approaches have developed to the point that they may be considered likely as replacements for MA-based processing. As a further alternative, melt spinning is explored in this study. Melt spinning involves non-equilibrium, high-speed solidification by rapid quenching of a molten alloy into a ribbon morphology of usually < 50 lm thickness.[18] Cooling rates above 105 K/s are generally
quoted for melt spinning[18] but solidification (solid/ liquid interface) velocity is a more meaningful description of the conditions under which the as-spun microstructure forms, and speeds >> 1 mm/s are common.[19,20] As the interface moves at these high speeds, thermodynamic equilibrium between liquid and solid phase co
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