利用直流复合电镀方法将WC纳米颗粒均匀分散到Ni镀层,用微米压痕仪测试了镀层的力学性能, 用动电位极化曲线研究了镀层在pH=9.0的0.05 mol/L H₃BO₃+0.075 mol/L Na₂B₄O₇缓冲溶液中的电化学性能. 结果表明, 与纯Ni镀层相比,纳米复合镀层的晶粒尺寸显著减小, 约为21 nm; 硬度提高了81%, 达到651 HV;自腐蚀电流密度降低约一个数量级, 约为1.29×10^-7A/cm²;破钝电位基本一致, 但致钝电位(10 mV)更低, 维钝电流密度(1.79×10^-6 A/cm²)更小,仅为纯Ni镀层的1/7. 利用Mott-Schottky理论结合点缺陷模型分析表明: 表面钝化膜仍具有p型半导体特征,WC纳米颗粒显著降低基体Ni的晶粒尺寸, 引起钝化膜中点缺陷密度和扩散系数的降低.

The metallic matrix composite with ceramic nano-particles has a wide prospect in many applications due to its superior properties. The nanocomposite Ni-WC coating has been synthesized by using DC co-electrodeposition of Ni with WC nano-particles. Its hardness was measured by using ultra-micro hardness tester. Its corrosion and passive properties were investigated in 0.05 mol/L H₃BO₃+0.075 mol/L Na₂B₄O₇ buffer solution with pH=9.0 by using potentiodynamic polarization measurement. As compared to pure nanocrystalline (nc) Ni, nanocomposite refined remarkably, with average grain size about 21 nm and the hardness increase of 80%, reaching about 651 HV. The corrosion current density i_corr is 1.29×10^-7 A/cm²,approximately one magnitude order lower than that of nc Ni. With the similar passive film breakdown potential, nanocomposite exhibits a lower passivation potential E_p of 10 mV and a much lower passive current density i_p of1.79×10^-6 A/cm², about 1/7 that for nc Ni. According to the Mott-Schottky analysis together with point defect model, the passive film on the nanocomposite exhibits p-type semi-conducting behavior,similar to that on the nc Ni. The grain refinement of Ni is beneficial to the reduction of both the donor density and diffusion coefficient.