Wettability and interfacial microstructure between Nd₂Fe ₁₄B and Nd-rich phases in Nd-Fe-B alloys

For achievement of high coercivity in Dy-free or-lean Nd-Fe-B permanent magnet system, understanding of reaction process between Nd-Fe-B main and Nd-rich phases is required. In this work, the wettability between Nd ₂Fe₁₄B and Nd-rich phases was investigated by the measurement of contact angles under isothermal heating. The activation energy for wetting was estimated by the time when the contact angle became constant and the activation energies for ternary and Cu-added Nd-rich ingots were 196.8 and 162.6 kJ/mol, respectively. Interfacial microstructure drastically changed at the temperature lower than the melting point of the Nd-rich ingots and the interface of Cu-added Nd-rich ingots became rough at lower temperature than ternary ones. It is concluded that Cu-addition is effective for the reduction of the activation energy of wetting and improves wetting behavior of Nd-rich phase.