Interplanar spacings of complex Fe-Ni phases in rapidly quenched Fe-Ni-Nb-B systems

Formation of phases in the course of crystallization from amorphous state in rapidly quenched Fe-Ni-Nb-B was investigated with respect to the ratio of Fe/Ni and content of B in a wide compositional interval. A transition from nanocrystalline bcc-Fe formed during first crystallization stage into fcc-FeNi and Fe23B6 fcc-type structure with large unit cell accompanied by a distinct change in the transformation kinetics was observed with increasing Ni content. The emergence of these phases during (nano)crystallization is investigated with respect to the changes of local order induced by large variations of Fe/Ni and to the presence of large atoms of Nb. Diverse methods of high-resolution structure characterisation are used to identify and quantify phases with similar interplanar spacing. A deviation from a typical two-stage pattern leading to a rapid single-stage crystallization with direct formation of stable phases, incidentally present also in the structure of the precursor master alloys, is interpreted within the framework of a model of cluster structure of amorphous state. Links between the expected local ordering in amorphous state and the structure of crystallizing phases are followed and compared with similar phenomena observed in Nb-containing Co-rich Fe-Co-Nb-B system.