Cu CLUSTERING AND Si PARTITIONING IN THE EARLY CRYSTALLIZATION STAGE OF AN Fe73.5Si13.5B9Nb3Cu1 AMORPHOUS ALLOY

Solute clustering and partitioning behavior in the early crystallization stage of an Fe73.5Si13.5B9Nb3Cu1 amorphous alloy have been studied by employing a three dimensional atom probe (3DAP) and a high resolution electron microscope (HREM). 3DAP results have clearly shown that Cu atom clusters are present in the amorphous state after annealing below the crystallization temperature. The density of these clusters are in the order of 10 m -3 , which is comparable to that of the α-Fe grains in the optimum nanocrystalline microstructure. In the early stage of primary crystallization, Cu clusters are in direct contact with the α-Fe nanocrystals, suggesting that each α-Fe primary particles are heterogeneously nucleated at the site of Cu clusters. In the early stage of crystallization, the concentration of Si is lower in the primary crystal than in the amorphous matrix phase, unlike in the late stage of the primary crystallization, where Si partitions into the α-Fe phase with a composition of approximately 20 at.%.