INFLUENCE OF IRRADIATION SPECTRUM AND IMPLANTED IONS ON THE AMORPHIZATION OF CERAMICS

Polycrystalline specimens of alumina (Al2O3), magnesium aluminate spin el (MgAl2O4), magnesia (MgO), silicon nitride (Si3N4) and silicon carb ide (SiC) were irradiated with various ions at temperatures between 20 0 and 450 K, and the microstructures were examined following irradiati on using cross section transmission electron microscopy. Amorphization was not observed in any of the irradiated oxide ceramics, despite dam age energy densities up to similar to 70 keV/atom (similar to 70 displ acements per atom). On the other hand, SiC readily amorphized after da mage levels of similar to 0.4 dpa at room temperature. Silicon nitride exhibited intermediate behavior, irradiation with Fe ions at room tem perature produced amorphization in the implanted ion region after dama ge levels of similar to 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 Si 3N4 did not appear if the specimen was simultaneously irradiated with 1 MeV He+ ions at room temperature. By comparison with published resul ts, it is concluded that the implantation of certain chemical species has a pronounced effect on amorphization threshold dose of all five ma terials. Intense ionizing radiation inhibits amorphization in Si3N4, b ut does not appear to significantly influence the amorphization behavi or of SiC.