Neutron irradiation and intergranular fracture in vanadium-20 wt% titanium alloys undoped and doped with phosphorus and sulfur

Abstract

The mechanical properties and grain boundary composition affected by neutron irradiation (9.8 × 10 24 n/m 2: E > 0.1 MeV at 438°C) in undoped, P-doped and S-doped V-20wt% Ti alloys all containing residual C and O have been studied using a small punch testing method and scanning Auger microprobe analysis. Neutron irradiation facilitated heterogeneous formation of intergranular microcracks, not leading to specimen failure, in all undoped and some-S-doped specimens. An irradiated undoped alloy indicated ductility loss to a smaller extent than expected from the easy microcracking due to a mixture of intergranular and transgranular macrocracking. The irradiation effect on the ductility varied in the S-doped alloy, while the irradiation exerted a beneficial effect on low temperature ductility in P-doped alloys. Intergranular S segregation in the undoped alloy and S desegregation in the S-doped alloy occurred during the irradiation. Unirradiated and irradiated P-doped alloys exhibited negligible S segregation and much smaller P segregation than the S segregation in the undoped and S-doped alloys. The grain boundary content of C affecting the ductility was remarkably reduced in the irradiated P-doped alloy and S-doped specimens with ductility loss. The ductility loss and improvement observed in the irradiated alloys are interpreted in light of the variations in segregation and precipitated impurities together with hardening behavior.