Influence of irradiation spectrum and implanted ions on the amorphization of ceramics

Polycrystalline specimens of alumina (Al₂O₃), magnesium aluminate spinel (MgAl₂O₄), magnesia (MgO), silicon nitride (Si₃N₄) and silicon carbide (SiC) were irradiated with various ions at temperatures between 200 and 450 K, and the microstructures were examined following irradiation using cross section transmission electron microscopy. Amorphization was not observed in any of the irradiated oxide ceramics, despite damage energy densities up to ∼ 70 keV/atom (∼ 70 displacements per atom). On the other hand, SiC readily amorphized after damage levels of ∼ 0.4 dpa at room temperature. Silicon nitride exhibited intermediate behavior; irradiation with Fe ions at room temperature produced amorphization in the implanted ion region after damage levels of ∼ 1 dpa. However, irradiated regions outside of the implanted ion region did not amorphize even after damage levels in excess of 5 dpa. The amorphous layer in the Fe-implanted region of Si₃N₄ did not appear if the specimen was simultaneously irradiated with 1 MeV He⁺ ions at room temperature. By comparison with published results, it is concluded that the implantation of certain chemical species has a pronounced effect on amorphization threshold dose of all five materials. Intense ionizing radiation inhibits amorphization in Si₃N₄, but does not appear to significantly influence the amorphization behavior of SiC.