Study Of Technical And Performance On Co-Cr Alloy And Its Nanocomposite Coating By DC/ PC Electrodeposition

In practical applications,metal materials often have low performance and low service life due to surface wear and corrosion.Compared with plasma spraying,high-velocity flame spraying,chemical vapor deposition and other means,electrodeposition is a simple and economical surface treatment technology.As an environmentally friendly and low cost process,trivalent chromium electroplating has developed rapidly in recent years.But a single chromium coating has a low corrosion resistance and low corrosion resistance.It is an effective means to optimize the properties of the chromium plating layer by introducing co plating metal?such as nickel and cobalt?into the bath.Cobalt chromium alloys are used in mechanical,chemical,aerospace,automotive,medical and electronic industries because of their good wear resistance,corrosion resistance and biocompatibility.In this paper,Co-Cr alloy and Co-Cr-SiO₂ nanocomposite coatings were prepared by direct current?DC?and pulse current?PC?electrodeposition.The main components of the bath are:Cr₂?SO₄?₃·6H₂O 140g/L,CoSO₄·7H₂O 50 g/L,sodium citrate 120g/L,sodium formate 65g/L,urea 65g/L,boric acid 50g/L,KBr 50g/L,NH₄Cl 50 g/L,saccharine 0.5 g/L,sodium lauryl sulfate 0.2 g/L and nano-SiO₂.The effects of bath composition,electrodeposition method,current density,bath temperature,plating bath speed,and plating time on the composition and properties of the alloy coating were studied.The optimum conditions for DC and pulse electrodeposition were determined by orthogonal test.The optimum conditions were as follows:pH 2.5,bath temperature30?,and plating time 45 min.The current density is 150mA/cm²,the stirring speed is150r/min,the duty cycle of the pulse current is 30%,the pulse current frequency is1000Hz,and the electrodeposition time is 45 minutes.The microhardness,surface morphology and corrosion resistance of the prepared Co-Cr and Co-Cr-SiO₂ coatings were tested.Compared with Co-Cr alloy and Co-Cr-SiO₂ nanocomposite coatings prepared under direct current conditions,the grain size of the coatings prepared under pulsed conditions is refined and the surface is dense.The microhardness is increased from538HV and 802HV to 689 HV and 957 HV,respectively.Corrosion testing in 3.5 wt%NaCl solution showed a corrosion rate of 0.0247 g/cm²h on the surface of the Co-Cr alloy coating,and a corrosion rate of 0.0121 g/cm²h on the pulsed Co-Cr alloy coating.The corrosion rate of the pulsed coating was lower.Moreover,the corrosion rate of both coatings is lower than the substrate's corrosion rate of 0.1088 g/cm²h,and the corrosion rates of DC and pulsed Co-Cr-SiO₂ nanocomposite coatings are 0.0102g/cm²h and 0.0079 g/cm²h,respectively;The test shows that the corrosion current density of DC and pulsed Co-Cr alloy coatings is 1.439×10^-4A/cm² and0.7114×10^-4A/cm²,and the corrosion potential is-0.89V and-0.86V;The corrosion current density of the SiO₂ nanocomposite coating of the DC and pulsed Co-Cr is0.78×10^-4 A/cm² and 0.332×10^-4 A/cm²,and the corrosion potential is-0.82 V and-0.75 V,respectively.The introduction of nanoparticles improves the microhardness and corrosion resistance of the coating.