SYNTHESIS OF NOVEL Ni-CrN HARD COMPOSITE COATINGS

摘要

A novel hard coating was fabricated using a two-step process: first, to deposit Ni-10.8 wt.%Cr or Ni-30 wt.%Cr nanocomposites on a nickel plate by co-electrodeposition of nickel with Cr nanoparticles from a citrate bath; second, to nitride the nanocomposites at 560°C,for 10h by means of plasma nitridation method. Vickers microhardness measurement showed that the surface hardness of the Ni-10.8 wt.%Cr and Ni-30 wt.%Cr nanocomposites after nitridation was 600-700HV and 1500Hv (50g loading), respectively, which was greatly increased as compared to the hardness of original nanocomposites (ranging from 200-300Hv). The microstructure of the Ni-Cr nanocomposites after nitridation was investigated by XRD and EPMA. Cross-sectional morphologies indicated that the content of the Cr nanoparticles codeposited had a significant impact on the microstructure of the nitrided nanocomposite. The nitridation of the Ni-10.8 wt.%Cr formed a double-layered structure. It consisted of a continuous inner layer of CrN and a thick outer layer with CrN precipitates dispersion. In contrast, a thin outer continuous CrN layer and a thick CrN precipitates dispersed inner layer was formed on the nitrided Ni-30 wt.%Cr nanocomposite. The dependence of the microstructure of the nitrided Ni-Cr nanocomposite on the content of the Cr nanoparticles is discussed in detail.