MICROSTRUCTURAL CHARACTERIZATION AND HARDNESS OF ELECTRODEPOSITED NICKEL COATINGS FROM A SULFAMATE BATH

Pure nickel plates were produced from a sulphamate bath by electrodepo sition. A systematic variation of the current density, in the range 0. 005 to 0.25 Acm(-2), resulted in a variation of the coating microstruc ture and properties. Deposits plated below a current density of 0.01 A cm(-2) had a surface morphology consisting of large, deep crevices sur rounding smaller substructures. A banded or laminar type microstructur e was observed in cross-section. Above this current density, truncated pyramidal structures, with ridged terraces oriented perpendicular to the growth direction, were found on the surface. The planar dimensions of the pyramidal surface features were found to increase with current density, as well as the columnar grain widths observed in the cross-s ectional view. To evaluate the mechanical properties of the coatings, microindentation hardness tests were performed using a Knoop indenter. A Hall-Petch type relationship for the samples deposited at and above 0.01 Acm(-2) was seen. (C) 1998 Chapman & Hall.