Investigating the effect of helium ion irradiation on deformation behaviour of Ni-Mo-Cr alloy via in-situ micro-tensile testing

Abstract

In this study, α particle radiation damage through transmutation of Ni anticipated in a Molten Salt Reactor (MSR) core candidate material is simulated through irradiation of nickel-based alloy, GH3535, with 5 MeV helium ion dose of 1.5 dpa at room temperature via use of a degrader wheel to ensure near-uniform radiation damage throughout a 10 µm depth. For both the unirradiated and irradiated samples, micro tensile specimens 5 × 5 µm in cross sectional area and ∼17 µm in length are fashioned (using focused ion beam milling) out of regions having single crystals and those including grain boundaries and subsequently tested in tension to failure. Surprisingly, micro-tensile results reveal that voids and displacement damage introduced via irradiation did not embrittle the GH3535 appreciably as there was not a statistically significant difference in their elongation to failure, despite an increase of the Critical Resolved Shear Stress (CRSS) from 200 MPa to 361 MPa. It was also observed that all samples including both unirradiated and irradiated grain boundary micro-tensile samples failed within a grain rather than along the grain boundary proving GH3535 fails trans-granularly even after helium ion irradiation. The implication of the results and comparison with existing literature data are discussed further in this paper.