Abstract
Pure Ni as well as the intermetallic compound Ni4Mo have been irradiated by α-particles at a high energy (29 MeV) and by 1 MeV electrons. In both cases, irradiation defects (vacancy-type stacking-fault tetrahedra and dislocation loops) are found. Under particular conditions, in Ni4Mo these irradiation defects align either one-dimensionally or even two-dimensionally. For the electron-irradiated material a phase diagram for the occurrence of one-dimensional or two-dimensional ordering is established. High-resolution electron microscopy allowed us to identify the defects in both types of material as stacking-fault tetrahedra. It also enabled us to reveal the presence of replacement defects in α-irradiated ordered Ni4Mo.