Irradiation Hardening Of V-4Cr-4Ti And V-5Cr-5Ti Alloys Due To Helium Implantation And Atomic Displacement Damage

Vanadium alloys(V-Cr-Ti series)are important candidate materials for blanket components of fusion reactors.Irradiation response of vanadium alloys needs to be clarified for their application.In the present study,specimens of two alloys(V-4Cr-4Ti and V-5Cr-5Ti)were irradiated with energetic He ions and heavy ions to understand hardening of the alloys due to helium accumulation and cascade damage production.A layer of uniform helium concentration and atomic displacement damage in the specimens was produced by varying energy of He ions and heavy ions(N i,Sn).Irradiation hardening was tested by using the nanoindentation technique.The results show that the soft substrate effect(SSE)can be effectively avoided in the specimens irradiated with heavy ions(N i and Sn)with kinetic energies of a few Me V/u.The depth gradient of nano-hardness due to the indentation size effect(ISE)was readily analyzed by the N ix-Gao model.Values of nano-hardness corresponding to the infinite depth were obtained.The nano-hardness increases with displacement damage at low doses and tend to saturation at 4200appm/0.2dpa under He ion irradiation.Hardening by heavy ion irradiation to the same displacement damage was lower compared with He ion irradiation.The V-5Cr-5Ti alloy shows less hardening under the same irradiation condition compared with the V-4Cr-4Ti alloy.The Defects production under different irradiation conditions was analyzed by using the rate equation approach.The numerical calculation shows a more significant growth of dislocation loops under helium ion irradiation,which contributes to irradiation hardening.Mechanisms of Cr and Ti addition on irradiation hardening were discussed.