Microstructure and Wear Resistance of MAO Coatings of TC4 Alloy with Different Er2O3 Doping Amounts
Titanium and titanium alloys are widely used in vehicles,aerospace and other engineering fields due to their low density,high specific strength,good corrosion resistance and low modulus of elasticity.However,under actual service conditions TC4 titanium alloy often exhibits poor wear resistance and low hardness.Therefore,it is crucial to improve its friction resistance through suitable sur-face treatment techniques.Among the surface modification technologies,micro-arc oxidation surface modification technology is low-cost and environmentally friendly,and is suitable for preparing ceramic coatings on the surfaces of light metals such as titanium,mag-nesium,and aluminium to improve their service life and efficiency.Usually,micro-arc oxidation coatings have defects such as micro-pores or microcracks,which reduce the hardness and wear resistance of the matrix composite coating.To address this problem,the ef-fective means commonly used is to add special elements or compounds in the electrolyte to fill the microporosity and microcracks,forming a ceramic coating on the surface of titanium alloy with low porosity,good densification and wear resistance.Doping rare earth elements in the electrolyte can improve the performance of the coating.In this paper,Er2O3 particles were doped into the sodium sili-cate-based electrolyte,and the effects of different Er2O3 doping on the wear-resistant properties of micro-arc oxidation(MAO)coating of TC4 titanium alloy were investigated.X-ray diffraction(XRD),field emission scanning electron microscope(SEM),and laser con-focal measurement microscope were used to characterize the physical phase composition and morphology of MAO coatings.The hard-ness,friction coefficient,wear volume,and bond strength of MAO coatings were tested using a microhardness tester,friction and wear tester,Bruker optical profilometer,and coating adhesion scratch tester.The results showed that MAO coating on the surface of TC4 titanium alloy after micro-arc oxidation mainly consists of A-TiO2 and R-TiO2 phases,and the content of the hard phase R-TiO2 in the coating increases after doping with Er2O3 particles.Energy dispersive spectroscopy(EDS)results showed that the coatings con-tained the element Er,which proved that Er2O3 participates in the formation process of the coatings,and the changes of the porosity and thickness of the coatings were related to the doping of Er2O3 particles.Compared with the undoped MAO coating,when the doping amount of Er2O3 was 0.9 g·L-1,the porosity of the coating surface decreased from 45.0％±2.6％to 26.2％±3.1％.The thickness of the coating was(5.76±0.16)μm with the best densification and continuity,the hardness of MAO coating was increased by 27.96％,the surface roughness Sa decreased to 0.325 μm,the wear volume decreased by 28.57％,and the adhesion was increased by 54.3％.The friction coefficient of MAO coating was the smallest,about 0.5.Doping Er2O3 particles in the electrolyte could promote the generation of hard phases in the micro-arc oxidation coatings,effectively reduced the number of micropores on the surface of the coating,which was conducive to the reduction of defects within the coating,and improved the densification and microhardness of the coating.The doped Er2O3 particles could participate in the coating formation process,reduce the surface roughness,reduce the friction between the friction vice and coating friction collision,and improved the wear resistance of the coating.Excessive doping of Er2O,particles might lead to uneven grain growth,resulting in poor densification and uniformity of the coating,and a decrease in microhardness.In addi-tion,excessive erbium content might adhere to the surface of the coating and increased the surface roughness of the coating,which was unfavorable for further improvement of the wear resistance of the coating.
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