SURFACE & COATINGS TECHNOLOGY, vol.202, no.9, pp.1718-1727, 2008 (SCI-Expanded)
The effect of borohydride, thallium acetate, ethylenediamine and sodium hydroxide concentrations, and the coating bath temperature on both the coating rate and boron content of the electroless Ni - B films was investigated systematically. The Ni - B coating rate increased with the increase in thallium acetate and sodium hydroxide concentrations, but it was not very sensitive to the borohydride concentration. Below 90 g L-1 ethylenediamine concentration the coating efficiency was significantly low and above this value as the ethylenediamine concentration increased the coating rate decreased slightly. Below 85 degrees C the coating rate was very low and above this temperature it was insensitive to the bath temperature. The boron content of Ni - B film increased with the increase in the borohydride concentration and the bath temperature, and decreased with the increase in thallium acetate and ethylenediamine concentrations. Up to 50 g L-1 sodium hydroxide concentration, the boron content of the film increased and above this concentration it was insensitive to the sodium hydroxide concentration. As the boron content of Ni - B film increased, both the corrosion resistance and microhardness of Ni - B film increased. Heat treatment brought significant improvement in the microhardness but the corrosion resistance of Ni - B film was observed to decrease due to the disappearance of the amorphous characteristics of the as-deposited Ni - B film and the formation of the Ni - B compound phases. (c) 2007 Elsevier B.V. All rights reserved.