1.12.2.1 Radiation-Induced Obstacles to Dislocation Glide

Primary damage of structural materials is initiated by the interaction of high-energy atomic particles with material atoms to cause the energetic recoil and displacement of primary knock-on atoms (PKAs). PKA energy can vary from a few tens to tens of thousands of electron volt and the PKA spectrum can be calculated for a particular position in a particular installation.5 A PKA with energy >~1 keV gives rise to a displacement cascade that produces a localized distribution of point defects (vacancies and self-interstitial atoms, SIAs) and their clusters (see Chapter 1.11, Primary Radiation Damage Forma­tion). Further evolution of these defects produces specific microstructures that depend on the irradia­tion type, ambient temperature, and the material and its initial structure (see Chapter 1.13, Radiation Damage Theory). This radiation-induced micro­structure consists typically of voids, gas-filled bubbles, DLs (that can evolve into a dislocation network), secondary-phase precipitates, and other extended defects specific to the material, for example, SFTs in face-centered cubic (fcc) metals. These features are generally obstacles to the dislocation motion. Their size is typically6 in the range of nanometers to tens of nanometers and their number density may reach ^1024m~3. At this density, the mean distance between obstacles can be as short as ~ 10 nm, and such a high density of small defects, particularly those with a dislocation character, makes the mechanisms of radi­ation effects on mechanical properties very different from those due to other treatments.