Abstract: The undercooling of liquid metals an alloys provides and effective approach to rapid solidification. Usually the crystallization rate increases with undercooling, but crystallization can be thoroughly suppressed if undercooling is sufficiently large and quasicrystals or metallic glasses are consequently formed. The crystallization process of an undercooled melt involves two periods: an initial rapid solidification period accompanying recalescence and a slow solidification period after recalescence which is controlled by external heat extraction. Only when the melt is undercooled to the hypercooling regime can it be wholly repidly solidified. Competitive nucleation of stable and metastable phases, "dendrite-spherical crystal" transition, "regular eutectic-anomalous eutectic" transition, solid/liquid interface absolute stability, and segregationless solidification are characteristic of the solidification of highly undercooled metallic melts. Since the realization of large undercooling is not limited by melt volume, it is possible to prepare bulk microcrystalline, quasicrystalline and amorphous alloys.

Key words: undercooling, rapid solidification, liquid metals