Effect of neutron irradiation on Fe-Ni invar alloy

The objective of this study was to obtain thermodynamic equilibrium at low temperature using neutron irradiation, and to investigate the structural unevenness in Fe-Ni invar alloy. The specimens of 25 to 26 at.% Ni-Fe alloys were irradiated at the temperature below 473 K with the neutron flux of 1.72 x 1013 n/cm2 (E > 1 MeV) for six days. For the irradiated specimens, the Curie temperature was determined from the magnetization curves measured by a magnetic balance. The lattice constants were measured using an X-ray diffractometer. The following conclusions were obtained from the effect of neutron irradiation on the Curie temperature and the lattice constants of the Ni-Fe invar alloys. The neutron irradiation raised the Curie temperature of the Fe-Ni alloys, and its rising rate was larger as the Ni content was smaller. This results can be explained from the fact that the Fe-Ni invar alloy has a tendency to separate into two fcc phases with different Ni concentration. The significant change in the lattice constants due to the neutron irradiation was not observed in contrast with the result of Chamberod et al. (Asami, T.)