Radiation Response of a 12YWT Nanostructured Ferritic Steel
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1215-V06-02
Radiation Response of a 12YWT Nanostructured Ferritic Steel M. K. Miller, D. T. Hoelzer and K. F. Russell Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6136, USA ABSTRACT In order to evaluate the radiation response of 12YWT nanostructured ferritic steel to high dose neutron irradiation, the solute distribution, and size, number density, and compositions of nanoclusters in the unirradiated condition and after neutron irradiation to a dose of 3 dpa at a controlled temperature of 600 ºC were estimated by atom probe tomography. No statistical difference in the average size or size distribution of the nanoclusters was found between the unirradiated and irradiated conditions. Therefore, these nanostructured ferritic steels are promising candidate materials for use under extreme conditions in future generations of advanced reactors. INTRODUCTION Iron alloys have played an important role in key components of commercial nuclear reactors. For example, the pressure vessels of nuclear reactors are fabricated from a variety of pressure vessel steels, such as A533B, A302B and their Russian counterparts. These nuclear reactors were designed to operate for a minimum of 20 years at an operating temperature of less than 350 ºC. New generations of power generating systems are needed to meet future energy demands, which will require new materials with high tolerance to extreme environments typically end-of-life neutron doses of up to 200 displacements per atoms (dpa) at temperatures of up to at least 750 ºC. Although iron-based alloys are typically not considered for long-term use at high temperatures due to significant grain growth and coarsening of precipitates, one class of ferritic steels that is under consideration for these extreme environments is the nanostructured ferritic steels - formerly referred to as oxide dispersion strengthened (ODS) steels. Nanostructured ferritic steels, such as 9Cr, 12YWT, 14YWT and MA957 alloys are produced by mechanically alloying pre-alloyed metals and yttria powders. This fabrication method forces all the elements in the powders into solid solution [1] and produces a high concentration of vacancies, thereby creating a new class of materials with remarkable properties. Atom probe tomography (APT) characterizations have demonstrated that there are high number densities of titanium-, oxygen- and yttrium-enriched nanoclusters in these nanostructured ferritic steels [2-4]. The nanoclusters and the associated fine grain size are stable during high temperature isothermal aging at temperatures up to 1400 ºC [3] and during long term creep at elevated temperatures (850 ºC) [4]. Consequently, these unique materials are candidates for use under extreme conditions in future generations of advanced reactors. Atomic displacement cascades produced during neutron or ion irradiation may induce mechanisms that could potentially destabilize or destroy the nanoclusters, change the vacancy and interstitial atom distribution, and thereby change the properties.
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