Precipitate Dissolution by High Energy Collision Cascades *

The evolution of the microstructure during irradiation is now widely recognized due to: (1) radiation altered kinetic phenomena; (2) collisional processes by energetic cascades. In this paper, we investigate the specific nature of the collisionai interaction between energetic cascades and precipitates. A new Monte Carlo-based computer program, TRIPOS, has been developed for the TRansport of Ions in POlyatomic Solids. The computer code utilizes standard nuclear and electronic energy loss formulas, and compares well with experimental data on particle reflection, penetration and sputtering. One of the unique features of the code is its applicability to problems involving multispecie media in multilayers of 3-dimensional configurations. The interaction of neutron-initiate high energy collision cascades is demonstrated to result in the partial dissolution of precipitates. However, the maximum precipitate size that may be completely destroyed by a high energy collision cascade is only a small fraction of the cascade size. Matrix atom implantation inside precipitates as well as preferential sputtering of light atoms from the surface of precipitates into the matrix is demonstrated to lead to changes in precipitate stoichiometry.