Formation of ε-Fe_XN/BN magnetic nanocomposite and itsthermodynamic and kinetic analyses

A nanocomposite of nanometer-sized magnetic granular ε-Fe-XN embedded in a nonmagnetic amorphous boron nitride matrix was prepared by ball milling mixture of α-Fe and hexagonal boron nitride in argon atmosphere. The grain size of the ε-Fe-XN alloy was about 10-20 nm. The nitrogen concentration in the ε-Fe-XN alloy increases with extending milling time. Both thermodynamic calculation and the present experiment show that iron and nitrogen atoms have higher alloying driving force than iron and boron atoms. Analyses of thermodynamics and kinetics about formation of the ε-Fe-XN alloy suggested that the formation of the ε-Fe-XN alloy is related to amorphization of the hexagonal boron nitride and refinement of the α-Fe. It was found from the present experiment that a critical grain size of the α-Fe reacting with nitrogen in the amorphous boron nitride is about 8 nm.