Studies of Electroless Nickel Deposits with Low Phosphorus Content

SUMMARY

A useful coating technology for electroless Ni-1.5wt%P has been developed. The bath can work normally for more than 5 turnovers with a plating rate of 20 μm/h. In the as-deposited condition, Ni-1.5wt%P deposit is a supersaturated solid solution of P dissolved in a nanocrystalline Ni matrix with a grain size of several nanometers. The microstructure transformed into a larger grain size Ni matrix with dispersive Ni₃P precipitates with increasing the heat treatment temperature. Ni-1.5wt%P deposit possesses as-deposited hardness and wear resistance superior to Ni-10.5wt%P deposit. The microhardness and wear resistance can be further improved by proper heat treatment. The optimum wear resistance of Ni-1.5wt%P deposit corresponds to its peak hardness (annealing at 375°C for 1 h), whereas for Ni-10.5wt%P deposit the optimum wear resistance is obtained after annealing at 650°C for 1 h. Ni-1.5wt%Ppossesses a corrosion resistance in NaOH solution superior to conventional medium and high phosphorus deposits, which have much better corrosion resistance in NaCl and HCl solution. The rotating fatigue results indicate that electroless nickel deposits cause a decrease in the fatigue strength of 30CrMo steel, and increase the fatigue strength of LY12 alloy. Ni-1.5wt%P deposit demonstrates higher fatigue resistance than Ni-10.5wt%P deposit.

Keywords:

• Electroless nickel plating
• Phosphorus content
• Hardness and wear resistance
• Corrosion
• Fatigue