[3L01-05] Fusion Reactor Materials 1

[3L05] Effects of thickness of miniature specimens on creep properties of F82H steel

*Takuya Nagasaka¹, Jingjie Shen¹, Takeo Muroga¹, Masami Ando², Hideo Sakasegawa², Taichiro Kato², Hiroyasu Tanigawa², Takashi Nozawa² (1. NIFS, 2. QST)

Keywords:Small specimen testing technology, Blanket structural material, Surface effect

A reduced-activation ferritic/martensitic steel, F82H steel, is the primary candidate structural material for fusion reactor blanket. Neutron irradiation creep properties are evaluated using creep tubes with the wall thickness of around 0.2 mm. Since deformation volume is much smaller than that of standard size specimens, it is essential to reveal the specimen size effect on creep properties to validate the results by the creep tubes. The purpose of the present study is to investigate the effects of thickness of the miniature specimens on creep properties. The gauge thickness of flat-type miniature specimens varied from 0.14 mm to 1.2 mm. The gauge length and the width were 5 mm and 1.2 mm, respectively. The creep rupture time under 120 MPa at 650°C was around 200 h for specimens with 0.141 and 0.268 mm in thickness, which was shorter than 300~360 h for 0.525 mm-thick or thicker specimens. One of possible mechanisms for the accelerated creep in thinner specimens is additional deformation due to dislocation motion activated in the unconstraint surface grains.