Theory of irradiation swelling in materials with elastic and diffusional anisotropy

New critical quantities for bubble-void transition effects in irradiated materials are derived with account of elastic interaction between cavities, dislocations and point defects in the approximations of a weak elastic and diffusional anisotropy. The elastic anisotropy is shown to result in quadratic (in the gas pressure to shear modulus ratio) corrections to the cavity bias which can substantially increase the critical quantities for highly overpressurized gas bubbles. On the other hand, the diffusional anisotropy difference between point defects (essential in non-cubic metals) can either increase or decrease the critical quantities depending on the distribution of dislocations over crystallographic directions. In contrast to previous theories, the present one gives not only the onset of bias-driven void swelling but the corresponding mean cavity parameters as well. The maximum void density and the corresponding swelling rate in the post-transient regime are argued to be determined only by the mean dislocation density and material constants. The relationships among material constants are found by which the stabilization of gas bubbles occurs via the dislocation loop punching mechanism even at elevated temperatures. (orig.)