Radiation-enhanced diffusion in amorphous Ni-Zr studied byin situelectron irradiation in a transmission electron microscope

Radiation-enhanced diffusion (RED) in a Ni-Zr metallic glass has been studied by high-energy electron irradiation performed in situ in a transmission electron microscope. Irradiations have been carried out on thin foil cross-sectional specimens obtained from Ni-Zr bulk diffusion couples. The diffusivity under electron irradiation has been derived from the growth rate of a thin Ni-Zr amorphous film present at the Ni-Zr interface. Experimental results show that the Ni is the most mobile species in these experimental conditions and that radiation damage occurs in glassy metals at a lower electron energy relative to the corresponding crystalline compound. Moreover, the dose-rate sensitivity of RED appears to depend also on the energy of the electron beam. To explain this effect, the process of radiation displacement in metallic glasses has been modeled within the framework of the free-volume theory of the structure of metallic glasses. The results of this simple model can qualitatively explain our results as well as those relative to RED induced by high-energy ion irradiation.