Structural Changes Induced by Low-Flux Ion Irradiation in a Ni4Mo Alloy

Irradiation induced random displacements of atoms and replacement collision sequences are possible mechanisms for phase transformations as well as other physical properties changes as grain size variation and hardness increase or decrease. In this study Ni(4)Mo alloy samples were subject to low-flux bombardment by ion beams. This alloy has similar structure to the Hastelloy-C used in industry and to U(3)Si that is used as nuclear fuel. Sample regions were irradiated while the energy density of the bombarding beams was carefully controlled and the non-irradiated regions were kept close to room temperature. This way the irradiation induced temperature increase was highly localized creating "quench-like" conditions. After the irradiation, the samples were annealed at low temperature. Due to irradiation conditions there was a high density of nucleation sites favoring the formation of finer grain structures as well as localized phase transformations. The results showed that with the appropriate fluence and post-irradiation treatment, a coarse grained specimen can be forced to re-crystallize with a smaller grain size and manifest a specific change in hardening values due mainly to an order-disorder transformation [1,2].