| In order to improve the wear resistance and corrosion of steels, ceramic coatings were prepared on different kinds of steels by the technique of plasma electrolytic deposition (PED). The cathodic PED method was employed to prepare ceramic coatings on Q235 carbon steel and 30CrMnSi alloy steel in Al(NO3)3-ethanol solution(ethanol system). The anodic PED method was performed in NaAlO2-NaH2PO4 solution (aluminate system) and Na2SiO3-NaH2PO2 solution (silicate system), respectively, to prepare ceramic coatings on the steels. The microstructure of the coatings was systematically observed by SEM,XRD,EDS,FTIR and XPS,and the formation process of the ceramic coatings was also analyzed and the discharge model of the coatings was put up. The wear resistance, corrosion resistance, hardness and bonding strength of the ceramic coatings were studied by ball-on-disk tester friction and wear test, electrochemical test and in micro-hardness instrument , pull-off test and thermal shock method, respectively.The results show that the composition and structure of the coatings prepared in ethanol system on both Q235 carbon and 30CrMnSi alloy steels were similar. The coatings obtained were composed ofα-Al2O3 andγ-Al2O3, andα-Al2O3 was the dominated phase. Increasing the duty ration and current densities will be helpful for increasing the contents ofα-Al2O3 in the coating. The coating mainly consisted of Al and O elements. Only a little Fe, which was the main elements of in the substrates, was found in the interface of the substrates and the coatings. The coating only grew outward the surface of the substrate during its growth process. The coatings forming in aluminate system by anodic PED on Q235 and 30CrMnSi are composed of crystal phase of Fe3O4-FeAl2O4, the crystallinity of which was enhanced by increasing the current densities or the frequencies or prolonging the treating time, while coatings forming in silicate system were proved to be composed of non-crystal SiO2. The anodic PED coating forming on Q235 were mainly composed of Al, O, Fe, and a little P elements and coating on 30CrMnSi were mainly composed of Si, O, Fe and a little Mn,Cr and P elements. The elements in both Q235 and 30CrMnSi made contribution to composition of the coating during anodic PED. The coating grew both inwards and outwards the substrates.The coatings forming on Q235 obtained in ethanol system showed a low current density of 7.359×10-8A/cm2 and corrosion potential of -0.490V, the corrosion current density of which was decreased by 3 order of magnitudes compared to the substrate. Coatings forming on Q235 in aluminate system and silicate system showed corrosion current densities of 3.117×10-7A/cm2, 7.636×10-7A/cm2, respectively, and corrosion potential of -0.423V, -0.491V, respectively. The corrosion current densities of the coatings were decreased by 2 order magnitudes compared to the substrates. Coatings forming on Q235 in aluminate system showed the lowest friction coefficient of all the coatings on its surface, and coatings obtained in ethanol system ranked second. Coatings obtained from the above three systems exhibited highest hardness of 1896Hv,1201Hv, 987Hv, respectively, and highest bond strength of 7.8MPa, 21MPa, 15MPa respectively. In a word, coatings obtained in aluminate exhibited the best corrosion resistance and lower friction coefficient; coatings obtained in ethanol system exhibited the lowest friction coefficient and better corrosion resistance.The corrosion current density of coating forming on 30CrMnSi in ethanol system was also decreased by three order of magnitudes compared to 30CrMnSi substrate. The corrosion current densities of coating obtained in aluminate and silicate system were nearly decreased by 100 times than that of the substrate. Coatings on 30CrMnSi alloy steel in all electrolytes showed similar hardness and bond strength of coatings on Q235 carbon steel. The coatings obtained in ethanol system exhibited the comprehensive performance of corrosion resistance and wear resistance...
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