HYDROGEN DESORPTION AND INTERNAL-STRESS IN NICKEL COATINGS OBTAINED BY PERIODIC ELECTRODEPOSITION

Periodic electrodeposition is performed in order to determine to what extent a change in conditions for the desorption of hydrogen from nickel deposits, which is occluded during plating, can affect their internal stress. The duration of the pause (zero current), tau(off), is varied in the range 0-900 s and the plating period, tau(on) = 120 s, is kept constant, maintaining the structure unchanged. The variations of internal stress, microhardness, and coercivity of the electrodeposits obtained at different tau(off), are investigated. The amounts of hydrogen leaving the coating, both during the pauses and after the deposition is completed, are determined. A proof of the mechanical nature of intensive hydrogen codeposition at the beginning of nickel electroplating is obtained. It is shown that the desorption of hydrogen is responsible to a considerable extent for the high tensile internal stress observed in similar coatings.