Ion-irradiation induced amorphization and crystallization processes in TiNi shape memory alloys have been investigated. The primary concern is to clarify the relationship between the critical temperature for irradiation-induced amorphization and the thermal crystallization temperature. The critical temperature for irradiation-induced amorphization was 673K, however, the edge of the foil specimen crystallized during the irradiation at a lower temperature. The crystallization temperature of the specimen edge during irradiation decreased with increasing of incident ion energy. Thermal annealing experiments revealed that the thermal crystallization preferentially occurred at the specimen edge and the crystalline-amorphous (C-A) interface; The crystallization temperature of the preferential sites were 573K and 623K, respectively. These preferential nucleation indicate that the nucleation barrier dominates the thermal crystallization temperature; the critical temperature for amorphization is higher than the thermal crystallization temperature with no nucleation barrier.