Thermal stability and ion irradiation response of refined grained V – 4Cr – 4Ti

Abstract

Vanadium-based alloys such as V-4Cr-4Ti are of interest as candidates for low activation structural materials for advanced nuclear reactors. One of the major challenges of vanadium-based alloys is their thermal stability and improving their mechanical properties at higher temperature ranges (> 600°C). This work explores refining the grain microstructure of V-4Cr-4Ti by arc melting and subsequently large strain extrusion machining specimens to produce a multimodal microstructure largely composed of nanocrystalline and ultrafine grain sizes. In-situ thermal stability of the multimodal V-4Cr-4Ti to 800°C shows the formation of vanadium carbides with negligible grain growth. In-situ dual-beam 16 KeV He⁺ and 1 MeV Kr²⁺ ion irradiation performed at 700°C to a final dose of ∼5 displacements per atom show the formation of small cavities well distributed throughout the system, with preferential clustering at grain boundaries. This work provides insight into how the increased fraction of grain boundaries affect the simultaneous dual beam ion irradiation response of multimodal V – 4 wt.% Cr – 4 wt.% Ti at elevated temperatures. Analysis of the cavities reveal an areal density of 0.024±0.007 cavities/nm² and swelling of 0.236% after the dual-beam ion irradiation. Nanoindentation shows a ∼50% increase in hardening after the ion irradiation at 700°C.