Atomic bonding (i. e., metallic, ionic, covalent, and polar covalent) is a potential factor to consider when comparing the microstructural evolution between metals and nonmetals, or between different nonmetal­lic materials that may have varying amounts of direc­tional covalent or ionic bonds. For example, several authors have proposed an empirical atomic bonding

500nm

Figure 17 Comparison of the microstructure of Type 316 LN austenitic stainless steel and 9%Cr-2%WVTa ferritic/ martensitic steel after dual beam ion irradiation at 650°C to 50 dpa and 260 appm He. Reproduced from Kim, I.-S.; Hunn, J. D.; Hashimoto, N.; Larson, D. L.; Maziasz, P. J.; Miyahara, K.; Lee, E. H. J. Nucl. Mater. 2000, 280(3), 264-274.

criterion to correlate the amorphization susceptibility of nonmetallic materials.136’137 Materials with ionicity parameters above 0.5 appear to have enhanced resis­tance to irradiation-induced amorphization. However, there are numerous materials which do not follow this correlation,86’138’139 and a variety of alternative mech­anisms have been proposed to explain resis­

tance to amorphization. Atomic bonding can directly or indirectly influence point defect migration and annihilation mechanisms (e. g., introduction of recom­bination barriers), and thereby influence the overall microstructural evolution.