Phase composition and defect substructure of nickel alloyed with boron and copper by electric explosion of conductors

Abstract

Using methods of electron microscopy, we have discovered that combined electroexplosive alloying of nickel with boron and copper gives rise to a multilayer structure. An outer amorphous crystalline layer incorporating 2–3 nm nickel-and copper-boride, oxide, and boride-oxide crystallites is formed on the alloyed surface. The intermediate (subsurface) layer 1–2 µm thick is made up of NiB ₁₂ and Ni ₄ B ₃ crystallites 120–130 nm in size, with boron-and copper-oxide particles observed along the grain boundaries. The underlying thick layer exhibits a cellular Ni-Cu-B melt crystallization structure grading initially into a high-rate dendritic crystallization structure and then into a granular structure. The electroexplosive alloying process is found to bring into existence a high scalar dislocation-density substructure in nickel crystallites both in the alloyed zone and in the adjacent heat-affected zone.