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Journal Articles

Stability of $$gamma$$' precipitates in nickel based oxide dispersion-strengthened superalloys under high-temperature and heavy irradiation conditions

Konno, Azusa; Ono, Naoko*; Ukai, Shigeharu*; Kondo, Sosuke*; Hashitomi, Okinobu*; Kimura, Akihiko*

Materials Transactions, 60(11), p.2260 - 2266, 2019/11

 Times Cited Count:1 Percentile:6.35(Materials Science, Multidisciplinary)

A stability of cuboidal $$gamma$$' phase under heavy irradiation was studied for newly developed Ni-based Oxide Dispersion Strengthened (ODS) superalloy as a candidate for the core structural materials in VHTR or GFR. The ion irradiation was applied at 873K, 1073K, 1273K and the dose was 100 dpa. The $$gamma$$' phase remained the cuboidal shape at 873K but got out of the shape at 1073K after irradiation. Those growths can be explained by the Nelson-Hudson-Mazey (NHM) model. For the result of 1273K irradiation, however, huge $$gamma$$' phase appeared in the whole irradiated area at the post irradiation-observation. This behavior is interpreted in terms of disordering of the ordered $$gamma$$' phase due to cascade collision, and thus increasing Gibbs free energy of the disordered phase induces a change of the element distribution inside the irradiated area. The ordered $$gamma$$' phase was reproduced from the disordered state at the cooling after ion irradiation.

Oral presentation

The Stability of gamma prime phase in Ni-based ODS superalloy under heavy ion irradiation at high temperature

Konno, Azusa; Ono, Naoko*; Ukai, Shigeharu*; Kondo, Sosuke*; Hashitomi, Okinobu*; Kimura, Akihiko*

no journal, , 

A newly developed Ni-based Oxide Dispersion Strengthened (ODS) superalloy as a candidate for the core structural materials in VHTR or GFR is studied to evaluate the stability of cuboidal-gamma prime phase under heavy irradiation in the presence of oxide particles. The ion irradiation was applied at 873K, 1073K, 1273K and the dose was 100 dpa. The gamma prime phase kept the cuboidal shape at 873K and got out of the shape at 1073K after irradiation, where these growths can be explained by the NHM model. For the result of 1273K irradiation, where huge gamma prime phase appeared in the whole irradiated area, changing Gibbs free energy by irradiation could induce the order-disorder transformation.

Oral presentation

Irradiation effects on phase stability of $$gamma$$$$prime$$ precipitates in nickel based oxide dispersion-strengthened superalloys under severe conditions

Konno, Azusa; Ono, Naoko*; Ukai, Shigeharu; Kondo, Sosuke*; Hashitomi, Okinobu*; Kimura, Akihiko*

no journal, , 

It is essential to develop the structural materials in Very High-temperature Reactors (VHTR) or Gas-cooled Fast Reactors (GFR) which reactor core environment is severe as the temperature is over 1273 K and irradiation level is up to 100 dpa. In the past, Ni-based alloys which are superior to Fe-based alloys as high-temperature strength were studied because of its $$gamma$$ $$prime$$ precipitates for reactor core materials. However, $$gamma$$$$prime$$ dissolves and reprecipitates at grain boundaries by irradiation at about 873 K. In order to show the suppression of this embrittlement, we newly developed a $$gamma$$ $$prime$$ precipitation type Ni-based Oxide Dispersion-Strengthened (ODS) superalloy in which nano-sizeed oxide particles are finely dispersed. In this research, the stability of cuboidal $$gamma$$ $$prime$$ precipitates under heavy irradiation was studied for newly developed Ni-based ODS superalloys, to explore the suitability of these as core materials. The specimen composition was equivalent to the MS4 produced by modifying the commercial superalloy CMSX10 to which the oxide particles are added.

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