MICROSTRUCTURAL CHANGES INDUCED IN ZR3AL AND U3SI DURING IRRADIATION OF THE CRYSTALLINE STATE

Microstructural changes produced in both Zr3Al and U3Si during irradiation with 1.5 MeV Kr ions have been followed by in situ transmission electron microcopy. When irradiated at sufficiently low temperatures, Zr3Al and U3Si become amorphous. During irradiation of the crystalline state at higher temperatures, the crystal structures are first disordered at doses comparable to those required for amorphization at low temperatures, and the pre-existing twin structure disappears from view in TEM. Continued irradiation of the disordered, large crystal grains results in the formation of new grains on the scale of 10 nm. During additional irradiation, the new grains increase in number and grow in size. Electron diffraction shows that new crystalline grains initially exhibit a preferred orientation to the original crystal lattice that decreases with continued irradiation until development of a powder-like diffraction pattern. The fine grain materials are resistant to amorphization during irradiation at lower temperatures and require up to a twenty-fold increase in the ion dose required for amorphization compared to that of initially unirradiated material.