Preparation of Nanocrystalline NbN and (Nb, Al)N Powders by Mechanical Alloying under Nitrogen Atmosphere

  • Miki Masamichi
    Department of Materials Science and Engineering, Faculty of Engineering, Himeji Institute of Technology
  • Yamasaki Tohru
    Department of Materials Science and Engineering, Faculty of Engineering, Himeji Institute of Technology
  • Ogino Yoshikiyo
    Department of Materials Science and Engineering, Faculty of Engineering, Himeji Institute of Technology

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Elemental niobium powder and Nb50Al50 elemental powder mixture were milled in a vibrational ball mill, Spex 8000, under nitrogen atmosphere, and the structures of milled powders and their sintered materials were examined by means of X-ray analysis, SEM and HRTEM observations.<BR>The niobium powder absorbed 50 at% of nitrogen during milling. Several types of nitrides were formed during milling, i.e., γ-Nb4N3 (FCT), δ-NbN (FCC) and δ′-NbN (hexagonal) with increasing nitrogen content. The mean grain size of these nitrides were about 5 nm. After sintering the milled powder at 1573 K and above, the structure consisted of δ′-NbN and ε-NbN (hexagonal) phases, which were assumed to be formed during cooling from δ-NbN stable at the sintering temperature.<BR>The Nb50Al50 powder mixture absorbed also about 50 at% of nitrogen during milling and formed a solid solution nitride (Nb0.5Al0.5)N with NaCl type structure. By sintering the (Nb0.5Al0.5)N powder at 1573 K and above, the structure decomposed to stable phases of δ-NbN and AlN (hexagonal). In contrast to the case of the Nb-N system, the δ-NbN remained stable after furnace-cooling from sintering temperatures.

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