Helium effects in iron- and nickel-base developmental alloys

The void swelling of Ni-base gamma-prime precipitation strengthened single crystal alloy (TMS-12) and oxide dispersioned MA 754 and MA 956 was investigated using proton irradiation at temperatures ranging from 723 to 873 K. In TMS-12, the voids preferably formed on the precipitates-matrix interface. The swelling increased with increase of the irradiation temperature and the maximum swelling of 3% was obtained at 873 K, which was lower than that in 10% CW 316 and JPCA. The voids were found to nucleate preferably on the oxide-matrix interface in MA 754. The expected reduction of swelling was not obtained in this alloy. Only few voids were found and excellency in swelling characteristic was found in MA 956. The helium embrittlement of MA 956 was studied using the samples pre-injected with a beam of 26 MeV ³He from the NRIM compact cyclotron to concentration of 40 appm He at 873 K. The tensile test was carried out at 873 K varying the strain rate from 10^-3/s to 10^-5/s. Superplastic deformation was observable without helium implantation. The reduction of the total elongation due to helium was observed only at the strain rate of 10^-5/s.