The in situ ion irradiation capability of Argonne’s HVEM-Tandem User Facility has been employed to study effects of 1.5 MeV Kr+ irradiation and 300 kV electron irradiation on the crystallization of as-deposited and of partially crystallized 40 nm thick films of CoSi2. Ion fluxes ranged from 8.5×1014 to 6.8×1015 m−2s−1 for which beam heating effects may be neglected. The maximum electron flux at 300 kV was 0.8×1023 m−2S−1. The maximum temperature at which crystalline CoSi2 is amorphized by the ion irradiation of flux = 6.8×1015 m−2s−1 is between 250 and 280 K. At higher temperatures amorphous material crystallizes by growth of any preexisting crystals and by classical nucleation and growth, with radial growth rates which are proportional to ion flux. The average degree of transformation per ion is 4×10−26 m3 per ion. Thermally induced crystallization of as-deposited films occurs above approximately 420 K. For ion doses at least as low as 3.4×1016 m−2 ion irradiation at 300 K promotes thermal crystallization at 450 K, by virtue of enhanced apparent nucleation and at large doses, by enhanced growth rate.