STABILITY OF VOIDS IN NEUTRON IRRADIATED NICKEL

The formation and stability of voids introduced in high purity nickel by irradiation with neutrons in the temperature range 50 to 575 °C has been studied. Octahedral shaped voids form during irradiation at temperatures ≥ 260 °C (0.30 Tm). The size of the voids increases and the density decreases with increasing irradiation temperature, but the volume fraction of voids is relatively temperature independent. If nickel is irradiated at a low temperature (50 °C) and subsequently annealed at an elevated temperature, stacking fault tetrahedra are formed; voids do not develop. The voids present in the nickel irradiated at temperatures > 260 °C coarsen during isothermal annealing at 600 °C by the process of large voids growing at the expense of smaller voids. At higher annealing temperatures, the voids anneal heterogeneously and are completely annealed at 800 °C. The configuration and density of voids in the nickel is compared to that in copper, aluminum and molybdenum. © 1969.