Ion-irradiation-induced hardening in alloys of V-4Cr-4Ti and V-5Cr-5Ti

Abstract Background: Vanadium alloy (V-Cr-Ti) is an important fusion reactor candidate material due to its low activation characteristics, desirable high-temperature strength and good resistance to radiation damage. However, studies at lower temperature have shown a substantially reduced radiation resistance, manifested in a loss of ductility and enhanced hardening. Purpose: This work aims to investigate the irradiation hardening behavior of vanadium alloys under He-ion implantation and displacement damage, and provide an experimental evidence for optimizing the radiation resistance of vanadium alloys. Methods: In this study, irradiation of V-4Cr-4Ti alloy and V-5Cr-5Ti alloy samples were carried out with He-ions and swift-heavy-ions. A thick layer with a uniform damage distribution in samples was produced by varying energy of He ions, or by using an energy degrade wheel for swift-heavy-ion irradiation. The nanoindentation technique was used to measure the irradiation hardening. Cross-sectional transmission electron microscopy (TEM) sample fabricated from the irradiated samples were investigated with TEM. Results: The results show that the hardening saturation occurs when the dose of He-ion implantation is more than 4200 (Atomic parts per million, APPM)/0.2 (Displacement per atom, DPA). The irradiation hardening by He-ions is far larger than that by the swift-heavy-ions at the same displacement damage level. Conclusion: The phenomenon of the enhanced hardening by He-ions can be attributed to the accelerated formation of defect clusters due to the combination of He-atoms and vacancies. (authors)