| Since tantalum easily forms a Ta2O5film spontaneously,it has excellent corrosion resistance and wear resistance.And plasma electrolytic oxidation(PEO)can be used in valve metals such as aluminum,magnesium,zirconium,titanium and its alloys to form an in-situ oxide film,so tantalum plasma electrolytic oxidation technology can significantly improve its corrosion resistance and wear resistance.At present,there have been a few studies on the film formation of tantalum plasma electrolytic oxidation,but its coating formation mechanism has not been deeply studied.In this paper,the coating formation process and the accompanying spark discharge behavior of tantalum PEO were studied in silicate based,aluminate based and phosphate based electrolyte,respectively,and the corrosion resistance and wear resistance of the PEO coatings formed in the three systems were further analyzed,exploring the coloring process and principle of tantalum plasma electrolytic oxide film.It was found that the rise of negative voltage in the time-voltage curve was accompanied by changes in oxide film structure and spark morphology in 8g/l Na Si O3·9H2O+1g/l KOH.By exploring the film constant voltage waveform and cathodic polarization behavior before and after the rise of negative voltage,the negative voltage change was accompanied by morphological change behavior occurs in the PEO process,and is affected by the anode potential.The oxygen generated in the anode pulse discharge process is attached to the discharge channel mouth to block the hydrogen discharge from the cathode discharge,resulting in an increase in hydrogen evolution overpotential,and the structure of the PEO film layer changes from“nodular”for a denser“cake-like”structure,the amorphous Si O2in the later stage of PEO deposits directly on the oxide film to form a“coral-like”structure.As for the PEO process of 10g/l Na Al O2+2g/l KOH,due to the local high temperature in the discharge channel of the coating,?-Al2O3is generated in the discharge channel in large quantities,forming a thicker double-layer oxide film structure,the outer film is a porous layer containing?-Al2O3,and the inner film is a denser Ta2O5membrane.However,in the electrolyte of 10g/l Na3PO4·12H2O+2g/l KOH,due to the weak conductivity of the phosphate electrolyte,PO43-does not participate in the film formation in PEO process,and which forms a thin film.The PEO coatings formed in the three electrolyte systems have significantly improved the corrosion resistance of tantalum.And the corrosion current density of the sample treated with PEO in aluminate electrolyte for 10min is 1.03×10-9Acm-2,after immersed in 3.5wt%Na Cl solution for 160 days,the impedance is 1.03×108?cm2,and the corrosion resistance is the best,which is due to its dense inner film.Compared with the substrate,the corrosion resistance is improved by 3 orders of magnitude.The coatings formed by PEO has significantly improved wear resistance,and the wear mechanism has changed from abrasive wear to adhesive wear.After PEO treatment for 10min in the silicate electrolyte and aluminate electrolyte,the coatings were not damaged after the wear test,and the friction coefficients were 0.42 and 0.58,respectively.Among them,the wear rate of the coating PEO treatment in silicate electrolyte for 10 min is 1.97×10-5mm3/(N·m),which is an order of magnitude better than that of tantalum.In the early stage of PEO treatment,an anodized film is formed on the surface of tantalum,and the anodized tantalum film exhibited a variety of colors under the interference effect of light.The color change of the oxide film was controlled by the treatment voltage. |
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