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Abstract In this paper, two-layer structure oxide coatings on 304 stainless steel were fabricated by cathodic plasma electrolytic oxidation (CPEO) in borax and glycerin solution under different voltages. Surface morphology, cross-sectional microstructure and composition distribution were analyzed. The plasma parameters in discharge envelope around the samples were evaluated on basis of optical emission spectroscopy (OES). The temperature close to the surface inside the samples at different voltages is over 1273.15 K. The oxidation activation energy during the CPEO process on 304 stainless steel was 170.5 KJ/mol. In addition, the electron concentration under the voltages was about 9 × 1021 m−3–3 × 1022 m−3, which increased with increasing the applied voltage. The plasma electron temperature fluctuated between 3000 K–6000 K in the stable discharge stage under different voltages, which increased with the increase of voltage. Furthermore, OES confirmed that O particles in plasma envelope come from the decomposition of borax, glycerin and water in this electrolyte. Highlights • Characterize microstructure and composition of the CPEO coatings under different voltages • Measure the temperatures and calculate the oxidation activation energy of CPEO • Evaluate the plasma parameters in the discharge envelope on the basis of OES • Investigate the growth and oxidation mechanism of CPEO on 304 stainless steel [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a novel rapid surface hardening technology on steels, namely cathodic plasma electrolytic oxidation (CPEO), was introduced. The oxide coatings of 35μm–180μm thick on AISI 304 stainless steel were prepared by cathodic plasma electrolytic oxidation in 15% borax electrolyte with additive at 260V. The surface morphology, cross-sectional microstructure, composition and phase constituents of CPEO coatings under different treatment time were characterized. The hardness profiles of coatings were determined. Their tribological behavior was evaluated. It was found that the oxide coatings contained two layers: one loose outer layer which mainly consisted of Fe3O4 phase and one compact inner layer with Cr and Ni aggregation where FeCr2O4, NiCr2O4, Fe3O4 and FeO phases were detected. The microhardness of CPEO coating increased with increasing coating thickness, and its maximum microhardness was up to 1335HV. Pin-disk wear test showed that the CPEO coatings on stainless steel had a low friction coefficient close to 0.1 under dry sliding against ZrO2 ball. The wear rate of the thickest CPEO coating is two orders of magnitude lower than that of stainless steel substrate. So the CPEO coating had better wear resistance than the bare stainless steel substrate. [Copyright &y& Elsevier]

Abstract The oxide films on Q235 low carbon steel as a cathode were quickly prepared by cathodic plasma electrolytic oxidation (CPEO) in 80 vol% glycerol electrolyte within 9 min. The morphology, composition and microhardness of oxide films were analyzed. The corrosion behaviors of bare steel and CPEO films were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The optical emission spectroscopy (OES) was collected and the electron temperature in plasma discharge envelope was calculated. It was found that the CPEO oxide films contained FeO phase, Fe 2 O 3 phase and some dispersed carbon particles. The plasma discharge envelope contained many active carbon, iron and oxygen species. The electron temperature in the plasma discharge region was over 5000 K and meanwhile the surface temperature of steel is over 1000 °C. The CPEO oxide film on Q235 steel grew linearly with 10.89 μm/min. The CPEO treated Q235 low carbon steel had a good corrosion resistance with lower corrosion current density and higher impedance. Highlights • The CPEO film on Q235 steel grows linearly and oxidation reaction rate reaches 10.89 μm/min. • Electron temperature in discharge region is over 5000 K and surface temperature of steel is over 1000 °C. • Active carbon, iron and oxygen species in plasma envelope enhance rapid growth of oxide film. • CPEO treatment improves corrosion resistance of carbon steel by decreasing corrosion current and increasing impedance. [ABSTRACT FROM AUTHOR]

A cathodic plasma electrolysis method was employed to fabricate a diamond-like carbon (DLC)-containing carburized layer on T8 carbon steel. The carburized layer was analyzed by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Its tribological property was measured by the ball-disk friction and wear tester, and its corrosion behavior was evaluated by electrochemical method. The carburized layer contains the martensite, retained austenite and Fe3C phases. Plasma discharge reduces the activation energy of carbon diffusion into steel to 132.8kJ·mol−1 and increases the diffusion coefficient of carbon to 1.39×10−7 cm2 ·s−1. Meanwhile, plasma discharge on the T8 steel in glycerol electrolyte enhances the formation of DLC component. The sp3 C content for DLC component is up to 67.6%. Moreover, both the wear resistance and corrosion resistance of treated steel are improved. [ABSTRACT FROM AUTHOR]