A method of electroforming smooth, bright, iron-nickel alloy foil, of thickness about 0.1 111111, is developed. The electrolyte, mainly a solution of ferrous chloride and nickel chloride, is operated at a temperature of 95T, and at current densities of between 5 and 20 A/dm2. Below that temperature, and at current densities greater than 20 A/dm2, the foil becomes cracked. The amount of nickel co-deposited in the alloy can be increased up to a limit of 6.24 per cent, by reducing the current density and/or increasing the concentration of nickel chloride in the electrolyte. As the nickel content of the foil rises, the material suffers increasingly from hydrogen embrittlement. The main mechanical properties of the alloy foil are more affected by hydrogen embrittlement, the amount of which is influenced by current density and the concentration of nickel chloride, than by changes in grain size. This behaviour is in contrast with that of electroformed iron foil, for which the mechanical properties are largely controlled by the influence of. the current density and electrolyte temperature upon its grain size. However, when the other process conditions are held constant, the mechanical properties of the alloy foil behave like the iron foil in decreasing with increasing foil thickness, owing to increases in average grain size.
The problem of hydrogen embrittlement, which adversely affects the quality and mechanical properties of electroformed iron-nickel alloy foil, is considered. Heat-treatment, such as annealing, can reduce these effects of hydrogen embrittlement. The electroformed metal can also be converted to alloy steel by carburizing; and by other heat-treatments, such as hardening and tempering, a range of mechanical properties for the foil can be achieved.
Iron foil, ranging in thickness from 0.05 to 0.16 mm, has been prepared by electrodeposition with an electrolyte solution composed mainly of ferrous chloride. Bright, smooth foil is obtained for current densities of 10 to 30 A/dm2, provided that the electrolyte temperature is above 85°C. Techniques developed to measure the mechanical properties of such a thin material are discussed. Unlike conventionally produced foil, the values of the main mechanical properties of the electrodeposited material, e.g. tensile strength and hardness, increase with decreasing thickness. The properties can also be affected by the main process variables: for instance, the lower the electrolyte temperature, the higher is the tensile strength. These effects are explained in terms of changes in grain size of the foil which are largely influenced by the process variables.
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