Ion irradiation induced amorphization of precipitates in Zircaloy

Samples of Zircaloy-4 were ion irradiated at several doses and irradiation temperatures and studied using transmission electron microscopy to discern the amorphization and dissolution behavior of second-phase precipitates under irradiation. It is found that near the critical temperature for amorphization under neutron irradiation a similar amorphization morphology is obtained under proton irradiation as under neutron irradiation, that is, an amorphous layer starting at the precipitate-matrix interface and moving in with increasing dose. However, the rate of amorphous layer advancement is much slower than that seen under neutron irradiation, and saturates with dose so that it remains a partial precipitate amorphization, i.e., this precipitate amorphization mechanism does not lead to complete amorphization as it occurs with neutrons. The results indicate that the critical temperature for bulk amorphization is primarily dependent on the displacement cascade density achievable with the irradiating particle and secondarily with dose rate. Depletion of iron from the precipitates is also observed, although not directly linked to amorphization.