NANOCRYSTALLINE Ni_58.5Mo_31.5B₁₀ and Ni₆₃Mo₂₇B₁₀ ALLOYS: MICROSTRUCTURE AND ITS EVOLUTION AT ANNEALING

Abrosimova G.E., Aronin A.S., Zver'kova I.I., Kir'janov Yu.V., Shekhtman V.Sh

Institute of Solid State Physics RAS, Chernogolovka, Russia

The nanocrystalline structure formation in amorphous Ni_58.5Mo_31.5B₁₀ and Ni₆₃Mo₂₇B₁₀ alloys was studied by X-ray diffraction, transmission and high resolution electron microscopy. The annealing at 600^oC was shown to lead to the nanocrystalline structure formation in both alloys. The annealed samples consist of the FCC nanocrystals (diameter of nanocrystals is about 20 nm) with amorphous regions between them. The nanocrystals contain numerous stacking faults and microtwins. The grain size in the near surface layer was found to be larger than the grain size in the bulk. The lattice parameter in the near surface layer is smaller than lattice parameter in the middle of the sample. The nanocrystalline phase represents a Ni-based solid solution. The diffusion of Mo and B from FCC to the amorphous phase occurs at the annealing. It results in the lattice parameter change. The crystalline Ni₃Mo, Mo₂B, Ni phases form when the nanocrystalline phase decomposes. The crystallographic aspects of Ni₃Mo phase formation from the FCC nanocrystals are discussed.