ABSTRACT
INTRODUCTION ~ap id solidification is known to result in the formation of metastable material haracterized by (1) a supersaturation in defects (i. e . , refinement of the grain size 1 micro-and nanocrystalline material, high density of vacancies, or a lack o f rdering) , (2) a metastable extension of solid solubility abo e the equilibrium limi t, 3) the formation of nonequilibrium crystalline. quasicrysta lline or glassy phases . \t temperatures high enough for thermally activated proce ses to be operative , he defects can anneal out by relaxation processes. recovery or recrystall iza tion nd the metastable ph ases can transform by phase transformations into the stable quilibrium. The aim of this chapter is to give an overview of the principal mechnisms of thermally activated phase tran for mations in rapidly solidified materia ls nd to give a few examples of how this knowledge can even be used to produce nproved materials. All the fo llowing discussion o n phase transformation in rapidly olidified alloys is based o n a general theory of transformations in metals and alloys s give n for example by Christian [ 1].
