Effect of helium on high-temperature tensile properties and swelling of vanadium and vanadium alloys

From fifth symposium on engineering problems of fusion research; Princeton, New Jersey, USA (6 Nov 1973). Sheet tensile samples of V-15 wt% Cr-5 wt% Ti were implanted with ~25 atomic ppM of helium at the ANL Cyclotron and tested at temperatures from 650 to 900 deg C. When compared with the control samples, the helium-injected samples show an increasing loss of ductility with increasing temperatures above 700 deg C. The loss of ductility in the helium- injected samples is accompanied by transition from a ductile, transgranular fracture to a completely intergranular fracture. The control samples fracture transgranularly throughout the range of test temperature. The effect of helium on void swelling was studied in two grades of vanadium using heavy-ion bombardment. High-purity vanadium (145 ppM C + N + O) and commercial-purity vanadium (1220 ppm C + N + O) were bombarded with 3.25-MeV Ni/sup +/ ions at 650 and 750 deg C to a damage level of 60 displacements per atom after preinjection with helium. Quantitative microscopy of the irradiated samples showed that the overall swelling was unaffected at 650 deg C, but was significantly reduced at 750 deg C, if the helium content was increased from 10 to 100 atomic ppM. The reduction in swelling appears to be associated with the presence of a high concentration of small helium bubbles that act as the predominant sinks for the radiation-induced point defects. (auth)