Stress in Nickel Electrodeposits

SYNOPSIS

The stress developed in nickel electrodeposits from the earliest stages up to the stage of steady production of stress has been continuously measured, for a plain Watts bath and for baths containing typical stress-reducing agents.

Tensile stress developed in deposits from the plain Watts bath is reduced and finally made compressive in a continuous manner as the concentration of stress-reducing agent is increased. The “instantaneous stress” (the stress in any small increment of thickness) becomes nearly constant with thickness; it is not markedly influenced by the temperature or current-density of deposition.

The results are interpreted by means of vacant-site and dislocation theory. Tensile stress appears to result from the formation of an oriented array of edge dislocations initiated by surface vacant sites, the overcrowded side of each dislocation being the side remote from the growing surface. Compressive stress results from stress-reducing molecules being adsorbed at surface vacant sites and so initiating edge dislocations of the reverse orientation. The ratio of the concentrations of the two types of dislocation then determines the magnitude and sign of the stress, which thus changes continuously with the degree of adsorption.