Preparation Of Nickel-Cobalt-Based Nano-Composite Cooatings And Their Properties

Composite plating has been used widely in various fields because it is an effective way to obtain the composite coating by co-electrodeposition between metal ions and ceramic particles. It can improve physical and mechanical properties of the coatings to use under severe environments. Nano-particles with a series of excellent properties were added into the coatings, which can enhance overall performance of materials. In this work, Ni-Co/Y2O3 and Ni-Co/ZrO₂ composite coatings were prepared by adding nano-Y2O3 and ZrO₂ into Ni-Co-based electrolytes. We mainly studied the influences of varying process conditions on the properties of coatings such as micro-hardness, thermal shock resistance, wear resistance and so on.In this work, by studing the influence of surfactant type, current density, pH, addition of oxide particles on surface morphology, the contents of nano-particles, grain size and hardness of the composite coatings, the optimized plating process of Ni-Co/Y2O3 and Ni-Co/ZrO₂ composite coatings were obtained. The results were shown as following:?1? Optimized plating process of Ni-Co/Y2O3 composite coating: Ni?NH₂SO₃?2·4H₂O 300 g/L, Co?NH₂SO₃?·24H₂O 13.7 g/L, NiCl26 g/L, H3BO3 30 g/L, C12H₂5SO4Na 0.05 g/L, nano-Y2O315 g/L; pH=4.0, Current density i=1.0 A/dm2, temperature 45 ?, deposition time 30 min.?2? Optimized plating process of Ni-Co/ZrO₂ composite coating: Ni?NH₂SO₃?2-4H₂O 300 g/L, Co?NH₂SO₃?2-4H₂O 13.7 g/L, NiCl26 g/L, H3BO3 30 g/L, C12H₂5SO4Na 0.05 g/L, nano-ZrO₂15 g/L; pH=5.0, Current density i= 2.0 A/dm2, temperature 45?, deposition time 30 min.?3? Under optimized conditions, the Ni-Co/Y2O3 and Ni-Co/ZrO₂ compostie coatings were obtaine by plating. Y and Zr contents in coatings were 6.00% and 4.08%, respectively. Because of adding nano-particles, grain size of Ni-Co based composite coatings were decreased, its micro-hardness also increased from 349.24 HV to 467.23 HV and 550 HV, the adhesive stength of coatings and metal matrix were improved from 3.92 MPa to 5.08MPa and 5.65MPa, while their corrosion resistance were declined slighly.?4? Compared with Ni-Co/Y2O3, Ni-Co/ZrO₂ have higher micro-hardness, adhesive strength and corrosion resistance. In addition, Ni-Co/ZrO₂ also can supply higher wear resistance, wear coefficient decreased from 0.9 to 0.72. But Ni-Co/Y2O3 composite coating have better thermal shock resistance, which maybe was related with the influence of Y2O3 on growth mechanism of oxidation film.