Effect of Cu Addition on the Microstructure and Magnetic Properties of an Fe_3B/Nd_2Fe_<14>B Nanocomposite Magnet

The microalloying effect of Cu addition on the microstucture and magnetic properties of Fe_3B/Nd_2Fe_<14>B nanocomposite permanent magnets has been investigated. With the optimum heat-treatment condition, Cu-containing alloy exhibits a much finer nanocomposite microstructre. Three-dimensional atom probe (3DAP) results have revealed that Cu and Nd form a high density (〜10^<24>m<-3>) of Cu-Nd clusters containing 5.0 at.% Cu and 7.0 at.% Nd prior to the crystallization reaction of the Nd_<4.5>Fe_<76.8>B_<18.5>Cu_<0.2> amorphous alloy. These clusters serve as heterogeneous nucleation sites for the Fe_3B primary crystals. In the final Fe_3B/Nd_2Fe_<14>B nanocomposite microstructure, Cu dissolves uniformly in the Nd_2Fe_<14>B hard magnetic phase. Improved magnetic properties have been obtained in the Cu-containing alloy; these are attributed to the reduction in the grain size due to the addition of Cu.