Electroless deposition of Ni-Cu-P, Ni-W-P and Ni-W-Cu-P alloys

Interest in electroless plating of nickel-based ternary alloys has increased because of their excellent corrosion, wear, thermal and electrical resistance. They also possess good magnetic properties. In the present investigation, the effect of copper and tungsten in alkaline electroless nickel baths has been studied in depositing Ni-Cu-P and Ni-W-P alloys and also the synergistic effect of ions in depositing Ni-W-Cu-P alloys. Deposits were characterized using XRD, scanning electron microscopy (SEM), energy-dispersive analysis of X-ray (EDX) and atomic force microscopy (AFM) techniques. XRD results revealed that not much variation in structure and grain size has been found in Ni-Cu-P deposit. A decrease in phosphorus content and a marginal increase in grain size have been observed due to the tungsten addition in the Ni-P deposit. Addition of copper in Ni-W-P baths has resulted in a quaternary deposit, Ni-W-Cu-P, with increased crystallinity. SEM studies showed that presence of coarse nodules in ternary Ni-Cu-P and Ni-W-P deposits. Addition of copper in Ni-W-P baths has resulted in a very smooth deposit. Studies by AFM on deposits have proved that the copper has suppressed coarse nodules by inhibiting their growth in quaternary deposit. No considerable change in hardness has been noticed in both as-plated and heat-treated deposits due to the inclusion of copper in Ni-W-P deposit. A marginal improvement in corrosion resistance has been observed in quaternary alloy compared to ternary (Ni-Cu-P or Ni-W-P) alloys.