Effect of temperature on ultrasound-assisted electroless nickel-boron plating

Electroless nickel-boron coatings have several advantages over electroplated nickel and electroless nickel-phosphorous: they are harder than both other coatings and, as all electroless coatings, can be applied easily to complex shapes and all substrates, even non conducting ones, contrary to electroplated coatings. Preliminary testing has proved that ultrasound assistance helps improve their properties by increasing the plating rate while conserving the properties of the coating. In this study, the effect of plating temperature on mechanically agitated and ultrasonic assisted electroless nickel-boron deposition was investigated: deposition was performed in two different configurations: one with a classical mechanical agitation at 300 rpm and the other employing ultrasound at a frequency of 35 kHz. In addition, different temperatures in the 80-95 °C range were tested. The increase of plating rate previously observed was confirmed and it was possible to lower slightly plating temperature while conserving plating efficiency, which decreases evaporation of the solution. Morphological, mechanical, corrosion and wear characterization were performed on the coatings, as well as tribocorrosion studies in an alkaline environment (0.1 M NaCl). Ultrasound-assisted coatings presented tribocorrosion behaviour that was similar or better than the standard ones.