Investigating the Effect of Bath Composition on the Hardness of Electroless Ni-B Coatings

In recent years, electroless Ni-B coatings have attracted much attention because of their wear-resistance and having high hardness. In the present research, using a two-level factorial design with three center points, the effect of ethylenediamine, ammonia and stabilizer solutions concentration on microhardness of the coatings in heat-treated condition was studied. The results showed that ethylenediamine concentration had no effect on the microhardness, but it made the electroless plating solution more stabilized. The stabilizer solution had the highest main-effect in increasing the microhardness. Also the interaction between ammonia and stabilizer solutions was significant. The maximum achieved microhardness for the coatings was 1358 HV which had been achieved when the ethylenediamine and ammonia concentrations were at their highest level. Scanning electron microscopy revealed that the microstructure was granular. Also the X-Ray diffraction analysis showed that the microstructure of the coating is nano-scaled and consisted of Ni3B, Ni2B and probably crystalline Ni grains.