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Polycrystalline specimens of alumina (Al2O3), magnesium aluminate spinel (MgA1204), magnesia (MgO), silicon nitride (Si3N4) and silicon carbide (Sic) were irradiated with various ions at temperatures between 200 K 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-7 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 intemediate behavior;. irradiation with Fe* ions at room temperatm 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 the amorphizahon threshold dose of all five materials. Intense ionizing d a t i o n inhibits amorpkation in Si3N4, but does not appear to signtficantly influence the amorphimion behavior of Sic.

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Plan view and cross-section transmission electron microscopy was used to investigate the microstructure of magnesium aluminate spinel (MgAl2O4) following room temperature irradiation with either 430 MeV Kr, 614 MeV Xe, or 72 MeV I ions. The fluences ranged from 1×1016/m2 (single track regime) to 1×1020/m2. Destruction of the ordered spinel crystal structure on both the anion and cation sublattices was observed in the ion tracks at low fluences. At intermediate fluences, the overlapping ion tracks induced the formation of a new metastable crystalline phase. Amorphization with a volumetric expansion of ∼35% was observed in spinel irradiated with swift heavy ions (electronic stopping powers >7 keV/nm) at fluences above 1×1019/m2. These results demonstrate that swift heavy ion radiation can induce microstructural changes not achievable with conventional elastic collision irradiation at comparable temperatures.