Effect of Cu and Nb on crystallization and magnetic properties of amorphous Fe77.5Si15.5B7 alloys

The crystallization of amorphous Fe77.5Si15.5B7 with the separate and combined addition of Cu and Nb was investigated. The addition of Cu increases the (metastable) temperature and time region of coexistence of Fe3Si and the amorphous matrix phase. The Cu does not affect the microstructure. The addition of Nb leads to the formation of nanocrystals but, for higher contents, boride phases simultaneously grow with the Fe3Si phase. The combined addition of Cu and Nb enhances the stability of amorphous Fe77.5Si15.5B7 against crystallization, shifts the crystallization temperature to higher values and increases the region of coexistence of nanocrystalline Fe3Si and the amorphous matrix phase. Nb is responsible for the small grain size of the Fe3Si crystals, and Cu for the phase composition. The magnetic properties are strongly correlated with the microstructure. Low coercivity and zero magnetostriction can be obtained only with the combined addition of Cu and Nb.