Abstract
Mechanical grinding of Nd15Fe77B8 powders was carried out under argon, hydrogen, and nitrogen atmosphere. It was found that Nd15Fe77B8powders absorbed large amounts of hydrogen and nitrogen when mechanical grinding was performed in either hydrogen or nitrogen atmosphere. The absorption of hydrogen and nitrogen during mechanical grinding caused significant grain refinement but reduced the coercivity values. Heat treatment of the hydrides resulted in desorption of hydrogen gas. When the hydrides were annealed at relatively lower annealing temperatures, the resultant powders consisted of α-iron and neodymium phases and showed low coercvity values. On the other hand when the hydrides were annealed at relatively higher annealing temperature, the resultant powders consisted of Nd2Fe14B crystallites and showed high coercivity values. Heat treatment of the nitrides did not result in desorption of nitrogen gas but they decomposed into α-iron and neodymium nitrides.
