Dimensional changes of metallic glasses during bombardment with fast heavy ions

Abstract

Small strips of various metal-metalloid glasses and metal-metal glasses have been irradiated below 50 K with 360-MeV Xe ions. Special care has been taken to achieve a rather uniform energy deposition throughout the samples. Projectile implantation has been avoided. Prior to and after irradiation, the macroscopic dimensions of the samples were determined at room temperature. Above an incubation fluence of a few ${10}^{12}$ Xe ions/${\mathrm{cm}}^2$ all glasses have shown drastic, irreversible changes in sample dimensions. Density measurements exclude swelling as a possible explanation and demonstrate that the dimensional changes are anisotropic. Each ion acts like a hammer, i.e., above the incubation fluence the sample dimensions perpendicular to the ion beam grow indefinitely with increasing fluence, whereas the sample dimension parallel to the beam shrinks. A control experiment with several crystalline metals (Al, Cu, Fe, Nb, Pt, W) and alloys (${\mathrm{Cu}}_{55}$ ${\mathrm{Zn}}_{45}$, ${\mathrm{Cu}}_{70}$ ${\mathrm{Zn}}_{30}$, ${\mathrm{Ni}}_{80}$ ${\mathrm{Cr}}_{20}$, ${\mathrm{Ni}}_{90}$ ${\mathrm{Cr}}_{10}$, ${\mathrm{Fe}}_{70}$ ${\mathrm{Cr}}_{25}$ ${\mathrm{Al}}_5$) reveals that the occurrence of the dimensional changes is closely related to the amorphous structure. The results are explained by a model, which assumes that the passage of an ion generates locally high mechanical stresses, which release shear transformations. Similarities and differences between the present model and the well-known ion-explosion-spike model are discussed and compared with the experimental data.