Structural studies of secondary crystallization products of the Fe23B6-type in a nanocrystalline FeCoB-based alloy

A stable Fe23B6-type phase formed in a nanocomposite soft magnetic alloy Fe40Co40Nb4B13Ge2Cu1 after thermal treatment was investigated. The primary crystallization temperature and second crystallization temperature for this alloy were determined to be 405 and 740°C, respectively. After annealing the sample at 820°C for 1h, a Fe23B6-type phase (FeCoNb)23B6 was observed. The structural information was investigated by x-ray diffraction, transmission electron microscopy, and three-dimensional atom probe. The Fe23B6-type phase contains about 33±5at.% Fe, 38±5at.% Co, 7±1at.% Nb, and 20±3at.% B. The Nb atoms tend to occupy the 8c sites and Co∕Fe atoms occupy the 4a, 32f, and 48h sites of the Fm3m space group for this structure.