6533b86ffe1ef96bd12ce5b7

RESEARCH PRODUCT

Peculiarities of Forming of Magnetic Hardening in Sintered Nd15Fe76.2Ti1.0Al0.8B7 Permanent Magnet by Ageing

subject

description

Variations of the intrinsic coercivity ( i H c ) with ageing (at 293 to 1173 K for 0.45 to 57.6 ks) of sintered Nd 15 Fe 76.2 Ti 1.0 Al 0.8 B 7 have been investigated. The tests indicated minimum and maximum of intrinsic coercivity ( i H min c and i H max c ) at temperatures 725 K and 1025 K, respectively. The observed behaviour of i H c has been compared with microhardness measurements and microstructure observations (SEM, EDAX, domain structure (DS) and room temperature Mossbauer spectroscopy). SEM and DS investigations gave hints to a change in microstructure. Fitting of the Mossbauer spectra of permanent magnets for different i H c has shown that the magnetic hyperfine field Bhf of 8j2 and 16k2 sites is reduced with increasing i H c which seems to be connected with the replacement of Fe atoms in their sites by Al atoms during ageing. Moreover the higher value of i H c corresponds to the higher value of the line width. The i H max c corresponds to the microhardness H max V for the Nd2 Fe 14 B grain phase. The results suggest that the coercivity of investigated permanent magnet increases during ageing not only by further diffusion of Al into Nd 2 Fe 14 B phase, but also by better distribution of elements in the main phase and especially in grain boundary phases and removing the stress between the phases of the permanent magnet.