PRECIPITATION PHENOMENON IN STOICHIOMETRIC ND2FE14B ALLOYS MODIFIED WITH TITANIUM AND TITANIUM WITH CARBON

Precipitation phenomenon has been investigated in stoichiometric Nd2Fe 14B alloys modified with Ti and Ti with C. Precipitates can be used to inhibit grain growth and understanding the precipitation process is i mportant in order to form the most effective dispersion. In the Nd-Fe- B-Ti system, TiB2, and in the Nd-Fe-B-Ti-C system, TiC are found to be the precipitating phases. Depending on composition, the precipitates can form at high temperatures in the liquid, during cooling after soli dification, and during heat treatment. The precipitates form on grain or phase boundaries. The TiC precipitates typically form as discrete p articles while the TiB, precipitates form generally in a globular bunc hed-up fashion. After a homogenization heat treatment, the equilibrium solubilities of Ti and Ti with C in the Nd2Fe14B phase are found to b e 0.47 wt.% and less than or equal to 0.06 wt.% respectively. This mea ns that almost all of the alloyed Ti and C can be precipitated as TiC which returns the excellent intrinsic magnetic properties of the hard magnetic phase. Both the carbides and the borides are found to have ex cellent high-temperature stability and resist coarsening and dissoluti on at least to 1000 degrees C. Since Ti and C react to form TiC the am ount of hard magnetic phase is not reduced while Ti addition alone rea cts with boron and reduces the amount of hard magnetic phase if extra boron is not added.