Pd-Ni Based High Corrosion Resistance Coating On Stainless Steel Surface

Pd-Ni alloy is studied in a great number of fields,such as decoration,electric contact materials,electrocatalysis,organic synthesis etc.due to its relatively lower cost but great performance.Based on preparation of Pd-Ni alloy,Pd-Ni/TiO2 composite coating and Pd-Ni-W ternary alloy coating were electroplated on SS316L in this thesis,in which corrosion resistance was mainly focused on.The corrosion resistance of coatings was evaluated on electrochemical method.Morphology and structure were characterised with X-Ray Diffraction(XRD),Scanning Electron Microscopy(SEM),Energy Dispersive Spectrometer(EDS),Glow Discharge Optical Emission Spectroscopy(GDOES)etc.and the relation between structure and corrosion resistance were discussed as well.The study results can be summarised as follows:(1)Pd-Ni alloy coating and Pd-Ni/TiO2 composite coating were electroplated on SS316L through direct current under the current density of 1 A/dm2.The results of electrochemical testing showed that Pd-Ni/TiO2 composite coating had a lower value of corrosion current density and lager impedance arc in 20%H2SO4 solution at 60?.The XRD testing results indicated that composite coating owned smaller crystalline grain size in comparison with alloy coating.With 5 g/L TiO2 addition into electrolyte,it was also found that composite coating exhibited obviously different morphology compared with alloy coating.(2)Based study results above,electroplating process were optimised through control variates method,including current density,duty cycle,frequency and deposition temperature.The results showed that the optimised deposition parameters were 1 A/dm2 current density.0.8 duty cycle,1Hz frequency and 40? temperature.(3)Effects of concentration of TiO2 particles on coating structure and performance were studied in detail.The XRD results showed that TiO2 particles played a role in grain refinement and the crystalline grain size became smaller with the increment of TiO2 in electrolyte.Modified micro-morphology could be found on SEM images with the presence of TiO2 in the coating.With the excessive content of TiO2 in electrolyte,aggregated TiO2 on surface of deposited specimen was found.Furthermore,EDS and GDOES results indicated that TiO2 influenced the composition of the coating.With the increase of TiO2 in electrolyte,obtained specimens had a decreased content of Pd in the coating while Ni content saw a growing trend.In addition,GDOES results showed that TiO2 particles just existed in exterior of the coating.The electrochemical results showed that the specimen deposited from the electrolyte containing 5g/L TiO2 had the best corrosion resistance and corrosion resistance of deposited specimens reduced with a further addition of TiO2 in electrolytic bath?(4)Deposition process of Pd-Ni-W ternary was developed and coatings with various contents of Wwere obtained.With the presence of W,Pd-Ni-W ternary alloy coating had a grain refinement in comparison with Pd-Ni alloy coating.This conclusion was verified by results of XRD and cathodic polarisation curves.With increasing W in electrolyte,obtained specimens had a reduced content of Pd and increased content of Ni in the coating.A proper addition of W in electrolyte had a positive influence on corrosion resistance of Pd-Ni-W ternary alloy coating in hot sulphuric acid solution.In addition,the presence of W in the coating had a positive influence on micro-hardness.Furthermore,mechanical damage was not found on surface of Pd-Ni-W alloy coating after flowing experiment of gas-liqud.However,corrosion resistance of the specimen was accelerated in this condition.