Effects of 10Â MeV electron irradiation at high temperature of a Ni-Mo-based Hastelloy

A Hastelloy alloy was irradiated with 10 MeV electrons at 650 °C for 700 h to a total dose of 2×10−3 displacements per atom (dpa). The microstructure of irradiated and non-irradiated specimens of this alloy were investigated by transmission electron microscopy (TEM). The non-irradiated specimens were analyzed by 3-D atom probe tomography (APT) in a local-electrode atom-probe (LEAP™). TEM analysis before the irradiation detects small precipitates with a mean diameter of 22 nm, which are coherent with the FCC matrix. The number density of these precipitates is ∼7×1018 m−3. Electron diffraction patterns from these precipitates exhibit superlattice reflections corresponding to the L12 ordered structure. The chemical composition of the precipitates, as measured by APT, is around 75 at% Ni with additions of Al, Ti and Mo. After electron irradiation, small precipitates with an irregular morphology are observed. The number density of these new precipitates about 1020 m−3 is greater than that of the L12 ordered precipitates before irradiation. The L12 superlattice reflections disappear completely, instead diffuse diffraction spots are observed at 〈1120〉FCC, which is attributed to compositional short-range order (SRO). The results are discussed with respect to the influence of the electron irradiation on the morphology and structure of the ordered precipitates.