Nuclear Techniques ›› 2015, Vol. 38 ›› Issue (7): 70605-070605.

• NUCLEAR ENERGY SCIENCE AND ENGINEERING •

### Investigation of helium irradiation induced hardening in nickel-based alloy

LIU Zhe1,2,3 BAO Liangman1,3 LIU Ke1,2,3 LIU Renduo1,3 YE Bonian1,3 LEI Qiantao1,3 LI Yan1,3,4

1. 1(Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Jiading Campus, Shanghai 201800, China) 2(University of Chinese Academy of Sciences, Beijing 100049, China) 3(Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Chinese Academy of Sciences, Shanghai 201800, China) 4(ShanghaiTech University, Shanghai 200031, China)
• Received:2015-03-16 Revised:2015-04-25 Online:2015-07-10 Published:2015-07-10
• Contact: Yan Li E-mail:ly@sinap.ac.cn

Abstract: Background: Hastelloy-N alloy is selected as the structural material for molten salt reactor (MSR), however, it is well-known that helium atoms play an important role in nickel-based materials after severe neutron irradiation, since they can drastically alter mechanical properties, potentially embrittle materials even at low concentration. Purpose: This study aims to understand the hardening of Hastelloy-N alloy material caused by helium irradiation. Methods: Samples were irradiated by helium ions of various energies and intensities at room temperature. After annealed at temperature of 773 K, 873 K and 973 K separately, and some typical samples annealed at 873 K were chosen as objects of investigation. Nano-indentation technique was used to obtain the hardness; elastic recoil detection (ERD) was used to detect the helium concentration; and positron annihilation spectroscopy (PAS) was used to investigate S parameter. The microstructure was characterized by transmission electron microscopy (TEM). Results: The hardness of the Hastelloy-N alloys irradiated by He+ increased with the dose whilst the S parameter first increased with irradiation dose, but decresed after reach certain incident depth. After annealing, both the hardness and the S parameters decreased. The TEM image showed lots of radiation-induced defects after irradiation. The small defects were annihilated and 1-nm small helium bubble was observed after annealing. Conclusion: The large radiation-induced defects were believed to be the causes of the hardening. While the recovery of hardening after 873 K annealing was ascribed to the annihilation of the small defects, the desorption of helium and the decreasing number of HenVm.