Nanoindentation on V–4Ti alloy irradiated by H and He ions

V–4Ti and V samples were irradiated by H/He ions with various energies to produce a damage plateau in the region from surface to the depth of 1.5 um at room temperature. Nanoindentation was performed to investigate the hardening behavior of the two materials under irradiation. It is found that the relation of maximum depth of plastic zone and indentation depth is not a fixed value. The maximum depth of plastic zone decreases with increase of damage level. Nix and Gao model was used to fit the measured hardness to obtain a hardness value H₀ excluding indentation size effect (ISE), which can be used to characterize the hardening effect induced by irradiation. After fitting the data of H₀, it is found that there is an exponential relation between the H₀ and damage level for both the V–4Ti and V materials. When the damage level is higher than ∼0.2 dpa, the hardness increases slowly, this indicates a slow increase of pinning centers in samples at this damage level. Comparing the hardening fraction of V–4Ti and V samples, significant hardening can be seen for V sample, and it becomes severe especially at damage higher than ∼0.2 dpa. The irradiation hardening resistance property of V–4Ti alloy is better than that of pure V