Hydrogen atmosphere sintering of cobalt-samarium magnets

Cobalt-samarium magnets were sintered in hydrogen atmosphere without cracking problems. The furnace atmosphere was purged of hydrogen during cooling to preclude hydride formation. Specimens sintered in hydrogen attained higher densities (P>98%) than those sintered at temperatures up to 40°C higher in argon. The use of the hydrogen atmosphere led to substantially improved magnetic properties. The major improvement was in the magnetic induction. The degree of improvement was greater than could be accounted for by the increased density. A specimen sintered in hydrogen had a higher alignment ratio than one sintered in argon at the same temperature. Magnets sintered in hydrogen showed a pronounced difference in shrinkage behavior compared to those sintered in argon. The ratio of the shrinkage in the preferred magnetic direction to that in the cross-section was greatly reduced in hydrogen. A specimen sintered at 1110°C in hydrogen exhibited preferred grain growth in the magnetic direction.