S. Liesert et al., PREPARATION OF ANISOTROPIC NDFEB MAGNETS WITH DIFFERENT ND CONTENTS BY HOT DEFORMATION (DIE-UPSETTING) USING HOT-PRESSED HDDR POWDERS, Journal of alloys and compounds, 266(1-2), 1998, pp. 260-265
In this work HDDR powders were used for the preparation of highly dens
ified anisotropic NdFeB magnets by the die-upsetting process. HDDR pow
ders with different Nd contents (14 at %, 16 at % and 18 at %) and dif
ferent grain sizes were used in order to determine the most favourable
composition and microstructure for a production of crack-free magnets
with maximum texture and optimum magnetic properties. The powders wer
e hot compacted in vacuum at 725 degrees C and 150 MPa. Then the sampl
es were hot deformed in an argon atmosphere at 750 degrees C with a st
rain rate of 10(-3) s(-1). Using HDDR powders with grain sizes around
0.3 mu m, corresponding to a coercivity mu(O1)H(c) of 1 T, a Nd conten
t of 14 at % and a deformation degree of 0.9, a remanence of 1.2 T and
a coercivity of 0.7 T were obtained. However a large amount of cracks
were present in the die-upset sample with 14 at % Nd. By increasing t
he Nd content suppression of the cracks in the die-upset samples was a
chieved and an increase of the coercivity was observed, but the degree
of texture and the remanence of the sample an reduced. For a Nd conte
nt of 16 at %, crack-free magnets with a coercivity of 0.95 T and a re
manence of 1 T could be produced. (C) 1998 Elsevier Science S.A.