Irradiation induced precipitates in vanadium alloys studied by atom probe microanalysis

Radiation-induced titanium precipitates are a major cause of irradiation hardening in vanadium alloys, but microstructural information is still far from comprehensive. In particular, the nature of black dot clusters observed to form during irradiation at low temperatures is still not clear while the large size Ti-precipitates with platelet shapes are relatively well characterized. V–4Cr–(0.1, 1 and 3 wt%)Ti alloys were irradiated up to 0.2 dpa at 350 °C. In TEM observations, platelet precipitates on {1 0 0} planes were observed in V–4Cr–3Ti and V–4Cr–1Ti, while a high density of small defect clusters was observed as black dot contrast in V–4Cr–1Ti. Enrichment of titanium as well as oxygen and titanium oxide in the matrix were observed by three-dimensional atom probe microanalysis in all alloys. Small clusters with sphere shape were observed in V–4Cr–0.1Ti, while the platelet morphology was seen in the other alloys. The mechanisms of nucleation and growth of precipitates in vanadium alloys are discussed.