Characterization of oxide particles in ODS austenitic stainless steel after heavy ion irradiation up to high doses
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Characterization of oxide particles in ODS austenitic stainless steel after heavy ion irradiation up to high doses Hiroshi Oka1,*, Yosuke Yamazaki1, Hiroshi Kinoshita1, Naoyuki Hashimoto1, Somei Ohnuki1, Shinichiro Yamashita2, Satoshi Ohtsuka2 1 Faculty of Engineering, Hokkaido University, N-13, W-8, Kita-ku, Sapporo 060-8628, Japan 2 O-arai Research and Development Center, JAEA, O-arai, Ibaraki 311-1393, Japan ABSTRACT Oxide dispersion strengthened austenitic stainless steel (ODS316), which is based on advanced SUS316 steel, has been developed by mechanically alloying and hot extrusion. Hafnium and titanium were added to make a fine distribution of oxide particles. The stability of oxide particles dispersed in ODS316 under irradiation was evaluated after 250 keV Fe+ irradiation up to high doses at 500 °C. TEM observation and EDS analysis indicated that fine complex oxide particles with Y, Hf and Ti were mainly dispersed in the matrix. There are no significant changes in the distribution and the size of oxide particles after irradiation. It was also revealed that the constitution ratio of Ti in complex oxide appeared to be decreased after irradiation. This diffuse-out of Ti during irradiation could be explained by the difference in oxide formation energy among alloying elements. INTRODUCTION The oxide dispersion strengthened (ODS) steels have excellent thermal creep resistance due to a high density of small oxide particles dispersed in the matrix. Although ODS method has been applied for development of ferrite steels, they still have poor corrosion resistance compared to the austenitic steels. Instead, an ODS austenitic stainless steel, based on an advanced SUS316 steel, has been developed by mechanically alloying (MA) and hot extrusion with the addition of minor alloying elements. According to the recent researches on ODS ferritic steels with Y2O3, the addition of group 4 elements such as titanium (Ti) and hafnium (Hf) is effective to make finer particles dispersed [1]. Furthermore, the Ti-added-ODS ferritic steels indicated good creep rupture strength as the manufactured cladding tubes [2]. The development of finer oxide particle would be associated with the formation of complex oxides composed of yttrium and group 4 element, so that a small amount of Ti and Hf was added to the ODS austenitic stainless steel in the present research. Distribution of oxide particles in ODS steels is highly important because the high creep strength of ODS steels at high temperature is associated with the existence of oxide particles in the matrix. Thus, the stability of the oxide particles irradiated up to high doses needs to be examined and confirmed. For this purpose, the heavy ion irradiation would be an appropriate approach. We studied the stability of oxide particles in ODS austenitic stainless steel (ODS316) irradiated up to high doses using transmission electron microscope (TEM).
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EXPERIMENT An advanced austenitic stainless steel, PNC316 developed by Power Reactor and Nuclear Fuel Development Corporation (presently the Ja
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