Effect of Heat Treatment Temperature on the Structure and Corrosion Resistance of Electroless Plated Ni-W-P Coating

Electroless plated Ni-W-P coating was heat treated at different temperatures so as to increase its harness and improve its corrosion resistance. The effects of heat treatment temperature on the structure, corrosion resistance, hardness and surface morphology of the electroless plated Ni-W-P coating were investigated by means of scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. The corrosion behavior of the as-plated coating in H2SO4 with different concentra-tions was evaluated. Results show that heat treatment contributes to increased hardness of the coating, and the one heat treated at 400 ℃ has the highest hardness of 1 120 HV. The as-plated Ni-W-P alloy coating has amorphous structure. With the increase of heat treatment temperature, the coating experienced structural transformation from crystal to mixed crystal and crystal, and the grains of the coatinggradually grew up after heat treatment. Moreover, the corrosion re-sistance of the as-plated coating in 10% H2SO4 first increased and then decreased with the increase of H2SO4 concentration.