Preparation And Properties Of Ni-W Based Nanocomposite Coatings

Ni-W alloy coating have been widely applied in industries,such as mechanical,electronics and military,due to excellent properties,simple preparation,little environmental pollution.Nowadays,nanocomposite coating prepared by nanoparticles with special characteristics and matrix metal have received increasing attention.Compared with direct current electrodeposition,pulse electrodeposition can decrease concentration polarization and improve cathode activation polarization.Thus,we can prepare nanocomposite coatings showing excellent anti-corrosion performance,mechanical performance and catalytic performance by using the coordination advantage of multi-component materials and technology advantage of pulse electrodeposition.In this thesis,we have investigated the preparation and properties of Ni-W/MWCNTs?Ni-W/Si3N4?Ni-W/BN(h)nanocomposite coatings.The effect of the addition of MWCNTs in plating bath,current density and stirring rate on the content of MWCNTs in the coating was studied.In conclusion,the preferable parameters were addition of MWCNTs:3 g/L;current density:5 A/cm2;stirring rate:200 rpm.Compared with Ni-W alloy coating,Ni-W/MWCNTs nanocomposite coatings possess higher microhardness and the addition of MWCNTs would lead to an increase in microhardness of the Ni-W/MWCNTs nanocomposite coatings.The co-deposited MWCNTs nanoparticles in deposit decrease the wear rate and reduce the friction coefficient.The co-deposition of MWCNTs in the nanocomposite coatings obviously increased the corrosion resistance in neutral,acidic and alkaline 3.5wt%NaCl solution.The influence of the addition of Si3N4 nanoparticles,pulse frequency and duty cycle on surface morphology,structure and Si3N4 nanoparticles content of Ni-W/Si3N4 nanocomposite coatings was examined,and the optimal technological condition was:Si3N4 nanoparticles dosage:30 g/L;pulse frequency:1000 Hz;duty cycle:60%.The microhardness of Ni-W/Si3N4 nanocomposite coatings are much higher than that of Ni-W alloy coating and the highest value is twice as much as that of Ni-W alloy coating.The Ni-W/Si3N4 nanocomposite coatings have better corrosion resistance than the Ni-W alloy coating in 3.5wt%NaCl solution.The Ni-W/Si3N4 nanocomposite coatings show good tribological behavior,and with the addition of Si3N4 nanoparticles increasing,the wear rate of nanocomposite coatings firstly decreased and then increased.The impact of BN(h)nanoparticles dosage,pulse frequency and bath temperature on the surface morphology,microhardness and deposition rate was analyzed,and the result indicates that the optimal condition was:BN(h)nanoparticles addition:5g/L;pulse frequency;1000Hz;bath temperature:70?.The corrosion tests show that the addition of BN(h)nanoparticles in plating bath increases the corrosion resistance of Ni-W/BN(h)nanocomposite coatings firstly and then reduces the corrosion resistance.The Ni-W/BN(h)nanocomposite coatings revealed a low coefficient of friction and wear rate compared with Ni-W alloy coating,and the wear rate and friction coefficient decreased with increasing mass fraction of BN(h)nanoparticles.