Effects of preinjected helium in heavy-ion irradiated nickel and nickel-copper alloys

Abstract

Pure nickel and two nickel-copper alloys (Ni-10 at. pct Cu and Ni-50 at. pct Cu) containing 50 appm preinjected helium have been irradiated with 14 MeV nickel ions at a constant homologous temperature of 0.45T m to 3 to 5 dpa at a depth of 1 μm from the surface. The radiationinduced lattice defects have been analyzed by transmission electron microscopy (TEM) with samples prepared in cross section. In the helium preinjected region of the pure nickel specimen, a substantial density of voids with an average diameter of 35 nm was observed. The nickelcopper alloys were found to contain only a high density of small helium bubbles (under 5 nm in diameter) and dislocation loops. The density of both dislocation loops and helium bubbles increases with increasing copper content, while the size decreases. The observed resistance of the nickel-copper alloys to void formation regardless of the presence of helium bubbles is considered to be the result of local clustering of like atoms which generates a high density of traps, and, thereby, disperses vacancies and gas atoms.