**Hyosim Kim 1,\*, Tianyao Wang 2, Jonathan G. Gigax 1, Shigeharu Ukai 3, Frank A. Garner <sup>2</sup> and Lin Shao 2,\***


Received: 14 September 2019; Accepted: 11 October 2019; Published: 14 October 2019

**Abstract:** As one candidate alloy for future Generation IV and fusion reactors, a dual-phase 12Cr oxide-dispersion-strengthened (ODS) alloy was developed for high temperature strength and creep resistance and has shown good void swelling resistance under high damage self-ion irradiation at high temperature. However, the effect of helium and its combination with radiation damage on oxide dispersoid stability needs to be investigated. In this study, 120 keV energy helium was preloaded into specimens at doses of 1 <sup>×</sup> 10<sup>15</sup> and 1 <sup>×</sup> 10<sup>16</sup> ions/cm2 at room temperature, and 3.5 MeV Fe self-ions were sequentially implanted to reach 100 peak displacement-per-atom at 475 ◦C. He implantation alone in the control sample did not affect the dispersoid morphology. After Fe ion irradiation, a dramatic increase in density of coherent oxide dispersoids was observed at low He dose, but no such increase was observed at high He dose. The study suggests that helium bubbles act as sinks for nucleation of coherent oxide dispersoids, but dispersoid growth may become difficult if too many sinks are introduced, suggesting that a critical mass of trapping is required for stable dispersoid growth.

**Keywords:** oxide-dispersion-strengthened (ODS); ion irradiation; He implantation; dual-phase; ferritic-martensitic; self-ion
