ABSTRACT
If a melt is cooled at a sufficiently high rate it can solidify direct ly into a metastable state by bypassing nucleation and growth of the stable phase. T he te rm " metastabili ty" refers to an excess energy frozen-in during rapid solid ifica tion . implying that a metastable state is out of thermal equ il ibrium . In ge neral, a broad spectrum of metastable structures can be classi fied according to their e nergy in excess of that of the stable structure , measured in units of RTm. where Tm is the melting temperature of the respective material [1]. The morphological metastabi li ty of microcrystalline materials, compositionally modulated fi lms, and interphase dispersions arises from the interfac ial energy contributions ( -O.l RTm)· T he structural metastability of intermetallic compounds and amorphous solids is due to a higher Gibbs free energy of the metastable structure in comparison with that of the stable state ( - O.SRTm). Finally, compositional metastability exists in supersaturated solid solutions with a maximum excess energy up to RTm.
