Precipitation in Ni-Si during electron and ion irradiation

This study was undertaken to further investigate how the nature of the irradiation condition affects precipitation in a dilute Ni-Si system. Transmission electron microscopy (TEM) discs of a solution annealed Ni alloy containing 5 at% Si were irradiated with 400 keV Ar+ ions, 200 keV He+ ions and 1 MeV electrons at average displacement rates in the range 2 × 10−5dpa/s to 2 × 10−3dpa/s at temperatures in the range 25°C to 450°C. Samples irradiated with electrons were observed in situ in an HVEM, while ion irradiated specimens were examined in a TEM after irradiation. Precipitation of Ni3Si was detected by the appearance of superlattice spots in the electron diffraction patterns. It was found that as the mass of the irradiating species increased, the lower bound temperature at which Ni3Si precipitation was first observed increased. For electron irradiation, the lower bound temperature at 2 × 10−3dpa/s was ∼125°C, whereas for 400 keV Ar+ irradiation at a similar average displacement rate the lower boundary was approximately 325°C. This suggests that cascade disordering competes with radiation induced solute segregation.