Spatial distribution of primary radiation damage in microstructures

The leading theory of primary radiation damage in materials, by Norgett, Robinson, and Torrens (NRT), assumes that materials are homogeneous. This is inadequate for most engineering materials, which have rich microstructures. The lack of alternative theories has led to the widespread assumption that the microstructure only affects defect recombination and not defect production. We extend the NRT formalism to account for microstructural variations and explicitly include the damage caused in a phase by primary knock-on atoms that are produced in another nearby phase. Our approach reveals new insight on the interplay between radiation damage and microstructure, and converges to conventional NRT at suitably large length-scales. Applying it to real two-phase nuclear alloys we discover a reversal of primary radiation damage localisation when grain size is < 1 mu m: in some fine-grained superalloys more damage is produced in the matrix than the precipitates, and the opposite is true for coarse-grained superalloys of same composition.