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Ductility and chemical reactions at the interface between nickel and magnesium oxide single crystals Hasselman, Didericus Petrus Hermannus

Abstract

An investigation was conducted on the interaction between nickel metal and single crystals of magnesium oxide. The nickel was cleaned with purified hydrogen gas at 800°C and melted under vacuum (5 x 10⁻⁵ mm. Hg) in contact with the magnesium oxide. The interface was examined metallographic-ally. The formation of compounds at the interface was examined by X-ray diffraction techniques. The magnesium oxide was plastically deformed by thermal stresses which occurred on cooling. Slip occurred on four slip planes only. The slip sources were present in the surface at a depth not exceeding ten microns. They were in the form of dislocation half-loops introduced in the surface during cleavage. The introduction of these half-loops was due to the formation of cleavage steps. Rows of dislocation half-loops were due to the multiplication of a half-loop on a slip plane oriented in the direction of propagation of the cleavage crack. Bond formation consisted of the formation of a magnesium-nickel compound (Mg₂Ni). The bond strength exceeded the stress for brittle fracture of magnesium oxide. Attack of the magnesium oxide occurred preferentially at the perimeter of the interface. This led to groove-formation, which resulted in a large hysteresis of wetting. The diffusion of nickel into magnesium oxide seemed to take place mainly by diffusion along dislocations.

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