Hardening of copper surfaces by beryllium diffusion

The paper contains results concerning the hardening of copper surfaces by beryllium diffusion. The superficial alloy was obtained in a galvanic cell provided with beryllium anodes and copper plates or rods as cathodes. A molten salt electrolytic bath containing the LiF-KF-NaF ternary eutectic mixed with 25 mole % BeF2 was employed. When the circuit of the galvanic cell is closed by immersing the electrodes into the molten bath, beryllium ions diffuse through the molten electrolyte towards the cathode where they are discharged by the electrons that come via the external circuit. The beryllium atoms diffuse into the copper surface at 700°C, the working temperature. The beryllium coating obtained is composed of different phases, determined by the working conditions time period, cathode current density and BeF2 purity. These phases correspond respectively to ß-phase (Cu2Be) and γ-phase (CuBe). The two phases have hardnesses higher than either copper or beryllium. The hardness is constant over the entire thickness of the layer containing the same phase, which means that a diffusion process with reaction took place. The hardness at the interface layer-copper substrate has variable values. This means that diffusion of the beryllium into the copper begins with the formation of a solid solution that ensures a perfect adherence between coating and substrate.