STUDIES OF ELECTROLESS NICKEL-BORON ALLOY COATINGS

Electroless nickel-boron coatings were deposited on mild steel substrates at various temperatures and pH values from a bath containing dimethylamineborane reducing agent. The bath was formulated to produce deposits with approximately 5% boron content. The thickness time data obtained revealed linear deposition kinetics showing dependence on temperature and pH. The coatings developed through a nucleation and growth type process were microcrystalline in nature and were highly supersaturated with respect to boron. Thermal annealing induced decomposition of this supersaturated solid solution. A peak hardness value of 1000 Hv was obtained after annealing at 300-degrees-C for 1 hr. Softening resulting from annealing at higher temperatures (450-600-degrees-C) was caused by particle coarsening, loss of coherency and ultimately by matrix annealing.