The Effect of pH Value of Plating Bath on the Properties of Electroless Ni-P Coating on Phenolic Plastic Substrate

摘要

Electroless Ni-P coatings with different phosphorus contents have been developed to deposit on phenolic plastic in plating bath with different pH values. The effects of pH value on the phosphorus content and the microstructure were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The hardness of the coating was measured using Vicker's indenter and the wear resistance was evaluated by a block-on-ring wear tester under dry condition. The results showed that with the increase of the pH value ranging from 4.4 to 5.4, the phosphorus content exhibited a decreasing trend from 11.01 wt.% to 7.76 wt.% . The structure of the electroless Ni-P coating transformed from amorphous phase, to a mixture of amorphous phases and nanocrystalline, and finally to nanocrystalline phase with the decrease of phosphorus content. The wear resistance of phenolic plastic was obviously enhanced by plating Ni-P coating. The hardness increased with the decrease of phosphorus content. However, the wear resistance did not always follow the hardness, indicating that not only the hardness but also other factors, such as internal stress and surface morphology, had an effect on the wear resistance of Ni-P coating.