Preparation of nickel-coated tungsten carbide powders by room temperature ultrasonic-assisted electroless plating

In this paper nickel (Ni)-coated tungsten carbide (WC) composite powders have been synthesized by ultrasonic-assisted electroless plating with a simplified pretreatment at room temperature as the conventional sensitization and activation steps have not been employed. The growth mechanism of Ni layers and surface morphologies and composition of initial WC powders, pretreated WC powders and Ni-coated WC powders were analyzed by field emission scanning electron microscopy, and energy dispersion spectrometry. The results shows that uniform Ni-coated WC composite powders were successfully synthesized without conventional sensitization and activation steps by ultrasonic-assisted electroless plating at room temperature. The growth mechanism of Ni layers appears as follows: the surfaces of pretreated WC powders appear step-like defects which act as activated sites. Nucleation and the growth of nickel grains take place on the activated sites of pretreated WC powder, and the process repeats continuously on the lath particles with reticulate structure on the as-coated surfaces of previously deposited Ni-cells, finally Ni cells grow up and merge into a layer.