Transition metal carbide formation in the Nd2Fe14B system and potential as alloying additions

Precipitates controlling grain growth in rapidly solidified Nd2Fe14B-type magnets are commercially important for inhibiting gain growth during heat treatments or thermomechanical processing. Compound additions of Group IVA, VA, and VIA transition metals along with C were added to the Nd2Fe14B (2-14-1) system. Transition metal carbide (TMC) formation was found for the Group IVA and VA transition metals. All the TMC precipitates observed formed with a 1:1 stoichiometry. To be successful as alloying additions in the 2-14-1 system, additional criteria besides carbide formation are necessary. The alloying ability of each transition metal carbide system was graded using criteria that dealt with phase stability, liquid and equilibrium solid solubility, and high temperature carbide stability. The Group IVA TMC alloys satisfied the proposed alloying criteria and were found to be excellent additions. The Group VA alloys, while forming carbides, only partially satisfied the proposed alloying criteria. Finally, the Group VIA alloys did not form TMCs.