Cold compaction behavior of nano-structured Nd-Fe-B alloy powders prepared by different processes

The compaction behavior of nano-structured Nd₁₆Fe ₇₆B₈ (atomic ratio) alloy powders, which were prepared by three different processing routes including melt spinning, mechanical milling in argon, and mechanically activated disproportionation by milling in hydrogen, was experimentally investigated by cold compaction tests. The compactibility was evaluated by using the double logarithm compaction equation, and both the hardening exponent, m, and the compaction modulus, M, were figured out for three powders by fitting the experimental data with the theoretical equation. The results show that the as-disproportionated alloy powders exhibits the best compactibility. By conventional cold compaction at 1400 MPa, using the as-disproportionated alloy powders could reach an over 0.92 relative density, while the compact relative density for the other two powders was 0.8 under the same compaction conditions. Furthermore, the mechanisms responsible for the densification during compaction were discussed by referring to such factors as the powder morphology and phase constituent of the alloy powders.