SOLUBILITY OF TI WITH C IN THE ND2FE14B SYSTEM AND CONTROLLED CARBIDE PRECIPITATION

An investigation has been launched to understand the unique solubility of titanium with carbon in the Nd2Fe14B system. In order to restrict grain growth effectively, a stable dispersion of many fine precipitates must be formed. In order to form an effective dispersion, the solubilities of the precipitating elements should be understood. This includes the liquid and solid solubilities as well as the equilibrium and non-equilibrium solubilities. Samples made by ingot casting and melt-spinning were examined. The solubility limit of titanium and carbon in the liquid phase was found to be between 4 and 6 at.% Ti+C. Once the solubility limit of the liquid is exceeded, primary TIC precipitates form in the liquid at high temperatures. The maximum solid solubility in the 2-14-1 phase depends on the existence of other phases and is found to be cooling-rate-dependent. For TiC, the solid solubility is found to equal the liquid solubility. The cooling-rate dependence indicates that the titanium and carbon exist in supersaturated solid solution. The equilibrium solubility in the 2-14-1 phase is found to be less than or equal to 0.06 wt.% Ti. Owing to its favorable solubility, TiC is found to be an exemplary alloying addition in the Nd,Fe,,B system, and can be used to alter beneficially the extrinsic properties of the microstructure while maintaining the excellent intrinsic properties of the hard magnetic phase.