460 keV Xe 2+ ion bombardment at doses between 5-7 × 10 15 at./cm 2 has been applied to thin W films embedded in a Cu matrix, both at room temperature and at 10 K. Both W film broadening and shift are found to increase with smaller initial W film thickness, as determined with 2 MeV 4He + RBS. For an initial W layer thickness of 20-40 Å the shift is only ≈ 10 Å, but for smaller thicknesses the shift increases to 40 Å. This result is inconsistent with expectations based on an earlier proposed model of ion induced clustering of the W film. The W film shift appears to be due to a ballistic effect: X-TEM analysis of an irradiated 6 Å W film reveals an inward shift of 30 Å, in good agreement with a shift of 37 Å found by RBS. At 10 K the W film shift is identical to the one measured at room temperature. Similar irradiations have been performed for thin Au and Ta films in Cu, both at room temperature and at 10 k. For room temperature irradiations the shift appears to be independent of film species. A correlation is found between the film broadening and the heat of formation: the mixing increases with the chemical driving force in the three systems. These results are in good qualitative agreement with a recently proposed model concerning chemical effects in collision cascades. At room temperature the chemical effects become more pronounced because of radiation enhanced diffusion. Finally, 65 keV He irradiations reveal a dependence of the broadening on the energy density in the cascade.