Influence of spike current in different shaped waveforms on the hardness and grain size of nickel electroforms

This paper studies experimentally and theoretically the effects of a ramp-down spike-shaped waveform on the grain size and the hardness of nickel electroforms in pulse current electroforming. Experimental results show that the quality of the electroforms, in terms of hardness improvement, influenced by the types of waveform is in the order of: ramp-down and triangular, both with spike > rectangular with spike > ramp-down; and triangular, both with relaxation time > rectangular. Compared with the results for the conventional rectangular waveform, the experimental results show that the hardness value can be improved by about 46% when a ramp-down spike and a relaxation time are used in the case of triangular or ramp-down waveform. The finest grain size and the highest hardness value were obtained by using a ramp-down spike in either triangular or ramp-down waveform. These results are supported by theoretical predictions and study of the surface morphology of the electroforms using a scanning electron microscope.