Fatigue Crack Growth of Neutron Irradiated V-15Cr-5Ti and V-3Ti-1Si

Compact-tension (CT) specimens of the alloys V-15Cr-5Ti and V-3Ti-1Si were irradiated to 3.8 × 10²⁵n.m^-2 (E > 0.1 MeV), corresponding to 4.0 dpa, at the temperatures 500, 600 and 700°C. Some specimens of the alloy V-3Ti-1Si were doped with 100 appm ¹⁰B, which during the irradiation was almost entirely transmuted to helium. Following irradiation constant-load-amplitude crack growth was measured at 200°C in air. All tests were performed at one R-ratio of 0.1 and a frequency of 2 Hz. Although both alloys in unirradiated condition showed similar crack growth rates as a function of the stress intensity factor range, the irradiated alloys behaved differently. The fatigue crack growth rate of V-3Ti-1Si irradiated at 500°C was slightly higher, with a lower dependence on the stress intensity factor range, compared to the unirradiated material, while after irradiation at 600 and 700°C the fatigue crack growth rate approached that of the unirradiated material. On the other hand, the alloy V-15Cr-5Ti irradiated at 500 and 600°C showed irregular crack growth and a higher growth rate, indicative of local unstable crack growth. After irradiation at 700°C the fatigue crack growth rate of this alloy also approached that of the unirradiated reference material. Limited data indicate that helium, generated by (n,α)-reaction with ¹⁰B, had no effect on the crack growth rate.