Effect of complexing agents on properties of electroless Ni-P deposits

In the present study, the authors studied the effect of complexing agents on the formation and properties of electroless Ni-P coatings having high phosphorus. The experimental results indicated that the composition of Ni-P deposits was decided mainly by main salt ( nickel sulphate) and reducing agent ( sodium hypophosphite), the amount of complexing agents did not have important influence on phosphorus content. However, the amount of complexing agents could affect the surface morphology, plating rate and microstructure of electroless Ni-P deposits. By adjusting the complexing agents in plating bath, the high phosphorus ( 11-12 wt-%) Ni-P coatings consisting of almost fully amorphous phase or the mixture of amorphous and nanocrystalline phase could be obtained. The possible reason of forming nanocrystalline phase was explained through the concentration fluctuation causing by lots of complexing agents. The formation of nanocrystalline phase not only increased the hardness of electroless Ni-P deposits, but also improved the thermal stability.