Formation of nanocrystals in an amorphous phase of multicomponent systems

The effect of the concentration of alloying components on the crystallization of amorphous (Fe$_{73}$Si$_{13}$B$_{9}$)$_{1-x-y}$Nb$_{x}$Cu$_{y}$ and (Co$_{70}$Si$_{12}$B$_{9}$)$_{1-x-y}$Fe$_{x}$Nb$_{y}$ alloys has been studied by X-ray diffraction and transmission electron microscopy in a wide composition region. The formation of the bcc structures in both the alloy groups is shown to be substantially dependent on the alloying component concentrations. The bcc phase is found to form in the cobalt-based alloys in the concentration region, where it was not observed before. In the cobalt-based alloys, the bcc phase appears at a niobium concentration higher than 1 at % and the average bcc nanocrystal size varies from 40 nm (at 1 at % Nb) to 14 nm (at 5 at % Nb). In the Fe-based alloys, nanocrystals with the bcc lattice form at the copper concentrations of 0.45–1 at %, and the average nanocrystal size is dependent on the alloy composition and varies in the range 16–24 nm. The causes of the concentration dependence of the formation of nanostructures in these alloys are discussed.