Some peculiarities of the atomic structure of metallic phases formed during liquid quenching and solid state reactions

Abstract X-ray data are presented relating to phases formed in FeSiAl and NiNbAl systems in liquid quenching from melts and also in solid state reactions when the required degree of diffusion mobility is induced by exposure to ion radiation (NiNbAl alloys) or by mechanical treatment (NiTi, NiAl, FeZr, FeW). The phases formed in the course of crystallization under large overcoolings are treated as being thermodynamically stable or metastable. It is argued that the formation of a superlattice constitutes the general trend of the crystallization process under large overcooling conditions. The same thermodynamic approach has been applied to explain the solid state reactions. It is shown that the amorphous state of metallic alloys can be regarded as a metastable amorphous modification of certain chemical compounds.