A Study On Ni-P-BN(h) Electroless Composite Coatings

Electroless Ni-P process has been developed into an effective technique for surface treatment by virtue of self-catalutic mechanism on the substrate. Electroless composite coatings can be prepared by adding particles like BN(h),PTFE,graphite,MoS2 and so on in the electroless plating solution.This thesis aims to explore the best preparation process of the Ni-P-BN(h) composite coatings and to obtain the Ni-P-BN(h) composite coatings, and to study the structure and mechanical properties of the composite coatings.In the experiments, we firstly studied the effects of 12 different surfactants on dispersion and wetting of BN(h) particles, and the anionic surfactant STAB was chosen as the best surfactant. Then, we studied the impact of surfactant concentration,BN(h) particle concentration,pH value and stirring speed on the codeposition and the quality of the composite coating. And the optimal preparation condition is obtained as: temperature is 85℃; concentration of STAB is 0.08g/l; concentration of BN(h) particles is 4g/l; pH value is 4.9; stirring speed is 200r/min.Then, both Ni-P and Ni-P-BN(h) coatings are prepared under the optimum condition. The structure and mechanical properties are studied by using SEM,XRD,microhardness tester and friction and wear tester. The results show below: the content of phosphorus in both Ni-P and Ni-P-BN(h) coatings is nearby 6.5%, belonging to medium class and BN(h) particles distributed quite uniformly in the Ni-P-BN(h) composite coatings. After 400℃heat treatment, Ni3P precipited both in Ni-P and Ni-P-BN(h) coatings, with amorphous organization transforming to crystalline state., and the BN(h) particles has little effect on the heat treatment. The hardness of Ni-P and Ni-P-BN(h) coatings are greatly increased after heat treatment. Both Ni-P and Ni-P-BN(h) coatings have good bonding strength. The as-deposited Ni-P coating has the best corrosion resistance, while the corrosion resistance of as-deposited Ni-P-BN(h) coating is lower. The corrosion resistance of Ni-P and Ni-P-BN(h) coatings after heat treatment are the worst. The friction coefficient of as-deposited Ni-P-BN(h) coating is about half of that of as-deposited Ni-P coating, and the friction coefficient of Ni-P-BN(h) coating after heat treatment is still lower than that of Ni-P coating after heat treatment. The friction coefficient of both Ni-P and Ni-P-BN(h) coatings after heat treatment is lower than that of Ni-P and Ni-P-BN(h) coatings before heat treatment.