The formation, structure and properties of nanocrystalline Ni-Mo-B alloys

The structure, structure evolution and microhardness of nanocrystalline Ni- Mo-B alloys were studied by X-ray diffraction, differential scanning calori metry, transmission and high resolution electron microscopy and microhardne ss measurements. The nanocrystalline structure was produced by controlled c rystallization of amorphous alloys. The annealed samples consist of the FCC nanocrystals with the amorphous regions between them. The grain size of th e nanocrystals is about 20 nm and depends on the chemical composition of th e alloy. The chemical composition of the amorphous phase between the nanocr ystals changes at the annealing. A slight grain growth was observed when th e annealing time increases. The diffusion of Mo and B from FCC to the amorp hous phase occurs at the annealing. It results in the lattice parameter cha nge. The microhardness of the alloys increases during the annealing. The mi crohardness values are the same in all alloys before the nanocrystalline st ructure decomposition. The microhardness is inconsistent with the Fetch-Hal l equation. The microhardness of the alloys is determined by the microhardn ess of the amorphous phase bands located between the nanocrystalline grains . (C) 1999 Kluwer Academic Publishers.