Grain growth kinetics in sintered Nd-Fe-B magnets

The topology of the microstructure and the grain growth kinetics of Nd-Fe-B magnets have been examined after sintering-time intervals between 0.5 and 19 h by metallographic analysis. In dense magnets about 80% of the grains have 5 to 7 corners. The fraction of grains with >8 corners increases with sintering-time and the amount of liquid phase during sintering. The grain growth exponents amount to n/spl ap/25 to 30 for small grains (/spl Lt/10 /spl mu/m) and to n/spl ap/1 to 4 for large grains (/spl Gt/10 /spl mu/m) revealing the intensive growth of large grains. Dense Nd-Fe-B magnets with an average grain size between 6.2 and 7.4 /spl mu/m reach a maximum energy density of 53 MGOe.