Theoretical approaches of structural modifications induced by ion irradiations

Once the elementary excitation of solids by ion irradiation (electronic slowing down and nuclear collisions) has occurred, the microstructure ''slowly'' relaxes either by thermally activated point defect jumps or by athermal relaxation. Three main classes of stability criteria for phases under irradiation are briefly reviewed. Stored energy arguments seem to account for some cases of irradiation induced amorphization or compound destruction; coupling between point defects and solute fluxes accounts well for irradiation induced precipitation in undersaturated solid solutions and quantitative models as well as simple stability criteria are available. The phenomenology of ballistic effects has been reformulated and yields sophisticated tools to cope with observed stability inversions or bistability phenomena. In particular, cascade size effects on phase stability can now be modelled in a well founded theoretical manner. (author)