Bilayer samples of U/Al, U/Ti, U/Si, and U/C have been ion beam mixed with 400 keV Ar and U/Al with Xe ions at doses from 2 × 1015 to 1 × 1017 ions/cm2. Mixing experiments were performed at various temperatures between 77 and 420 K. The amount of interfacial mixing, 4Dt, follows a linear dose dependence below a critical temperature, depending on the system studied. Below this temperature, the mixing efficiency, defined as ∂(4Dt)Φ where 4Dt is the mixing and Φ is the dose, is temperature independent. Its value, as well as the value of the transition temperature, agrees well with the thermodynamical model of chemically biased diffusion in a thermal spike for the four systems tested. The transition between the thermal spike regime and the temperature enhanced mixing regime was interpreted on the basis of an intracascade mechanism. The formation of an intermetallic compound in the U/Al system was detected and interpreted on a qualitative basis by crystallographic considerations.