Network dislocation structures are routinely observed in metals5,8,200 and ceramics300,301 irradiated at
temperatures above recovery Stage I to temperatures in excess of recovery Stage V. During prolonged irradiation, the microstructural evolution typically involves formation and growth of faulted dislocation loops, loop unfaulting to create perfect dislocation loops, and then loop interaction/impingement to form network dislocation structures. The network dislocations are typically randomly distributed and are often heavily jogged as opposed to the relatively straight dislocations found in unirradiated metals. Figure 33 shows a typical network dislocation micro­structure for irradiated copper.30 The quantitative value of the dislocation density can vary significantly among different materials within the same crystal structure. For example, typical network dislocation densities in irradiated metals at temperatures between recovery Stages III and V range from -0.01 to-0.1 x 1014m~2 for Cu302-304 to-1-10 x 1014 m 2

for pure Ni304 and austenitic stainless steel.20