기계적 합금화에 의한 NiAl 나노결정립 금속간화합물의 형성 = Powder Matallurgy:Formation of NiAl Nanocrystalline Intermetallic Compound by Mechanical Alloying

다국어 초록 (Multilingual Abstract)

NiAl intermetallic compound was fabricated by mechanical alloying. The microstructure of the intermetallic compound was investigated as a function of mechanical alloying time and heat treatment condition by the combined analysis of XRD, neutron diffraction, SEM, and TEM. Mechanical alloying of Ni-50 at.%Al powders for 120 hours resulted in nanocrystalline grains with diameter of 2-5 ㎚. X-ray diffraction and neutron diffraction spectra indicated that only NiAl intermetallic compound was formed during mechanical alloying. NiAl superlattice peak (100) was still retained after mechanical alloying for 120 hours. Heat treatment of mechanically alloyed powders at 600℃ for 90 hours encouraged grain growth up to 20-30 ㎚, while long range order parameter remained almost constant. The lattice parameter was reduced from 2.903Å for as-milled NiAl compound to 2.884Å for the case of heat treatment at 600℃ for 90 hours. The activation energy for the reduction of lattice parameter was also evaluated as 0.5-0.7 kJ/㏖ as a function of heat treatment time by the Arrhenius equation. As the heat treatment temperature increased, the activation energy for the reduction of lattice parameter gradually decreased. It is concluded that the ordered nanocrystalline NiAl intermetallic compound was obtained by the ordering transition from topological disordered state during mechanical alloying of Ni-50 at.%Al up to 120 hours.