The Effect of Reducing Agent Concentration on Microstructure and Hardness of Electroless Ni-B Coatings

In the present research, the effect of borohydride ion concentration existing in the electroless plating bath on the microstructure and hardness of electroless Ni-B coatings in the as-plated and heat treated conditions has been studied. In order to study the structure of electroless Ni-B coatings, the surface and cross-sectional images were examined. XRD analysis of the as-plated and heat-treated coatings showed that the former has an amorphous structure, while the latter has a crystalline one. EDS analysis confirmed the presence of Ni, B, Fe and Pb in the coatings. Microhardness test results revealed that the increasing of sodium borohydride concentration during plating enhanced the microhardness of the coatings in the asplated and heat-treated conditions. Also, at constant concentration of sodium borohydride, applying the heat treatment led to increase the microhardness. The maximum microhardness for the as-plated and heat treated coatings were 854 HV50g and 1121 HV50g respectively.