Dependence of magnetic properties on microstructure in mechanically alloyed Nd-Fe-Ti-N

In the systems of NdxFe92-xTi8 and Nd8Fe92-yTiy, Nd-Fe-Ti intermetallic compound with ThMn12 structure has been successfully synthesized by mechanical alloying (MA) and subsequent annealing. It has been found that the ThMn12 structure exists only over a range of compositions 5 less than or equal to x < 11 and 6 < y < 16 for NdxFe92-xTi8 and Nd8Fe92-yTiy, respectively, annealed at 960 degrees C for 30 min. The Th2Zn17 structure for x greater than or equal to 11 as well as for either y = 2 or y > 16 and the TbCu7 structure for y = 4 can be formed, respectively. For Nd8Fe84Ti8, MA powder annealed at 650-850 degrees C, the phase of hexagonal TbCu7 structure is formed. With increasing the annealing temperature T-a, the metastable TbCu7 structure is transformed into the ThMn12 structure. The Curie temperature increases from 180 degrees C for the TbCu7 structure at T-a = 650 degrees C to 300 degrees C for the ThMn12 structure at T-a = 1050 degrees C. The nearly complete transformation from TbCu7 to ThMn12 may be achieved at T-a = 960 degrees C. All the MA prepared samples are nitrided at T-N = 400 degrees C for 15 h and the nitrogenation raises the Curie temperature T-c of the phase with the ThMn12 structure to 400-450 degrees C. Too high temperature of the nitrogenation leads to decomposition of the compounds. The dependence of the magnetic properties on the composition and heat treatment and nitriding conditions has been studied.