Effect of Tungsten Addition on the Anti-fouling Property of the Electroless Ni-W-P Deposits

Ternary Ni-W-P deposits were prepared on the mild steel (1015) substrate using electroless plating by varying sodium tungstate concentration. Surface morphology, microstructure, and the microhardness of electroless Ni-W-P deposits were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and a MH-6 Vickers diamond indenter, respectively. The results demonstrate that the bath concentration plays a significant role in obtaining ternary Ni-W-P deposits containing various composition of phosphorus and tungsten, which decides the surface morphology and the structure. Although nodular formation is a common feature of electroless Ni-W-P deposits, the increase of tungsten content decreases the phosphorus content of these deposits and hence changes the composition of the nanocrystalline phase. The co-deposition of tungsten in the deposits increases the microhardness due to the solid solution strengthening of nickel induced by tungsten in the deposits which resists regional plastic deformation. Moreover, the results of differential scanning calorimetry (DSC) show that Ni-W-P deposits with high tungsten content exhibit higher crystallization temperature. Further fouling experiments indicate that the Ni-W-P deposit surfaces with different tungsten contents inhibit the adhesion of fouling compared with the mild steel surface. The experiments also indicate that the fouling adhesion rate is intimately related to the tungsten content. However, the relationship between the fouling adhesion rate and surface roughness of the ternary Ni-W-P deposits is not found in these experiments.