Study On The Corrosion And Wear Properties Of The Mao/CrN Duplx Coating On Magnesium

The micro-arc oxidation coating was prepared by micro-arc oxidation(MAO)technique on pure magnesium,then the CrN coating was deposited on top of the MAO coating by magnetron sputtering technique.The phase composition of the MAO coating and MAO/CrN duplex coating were identified by using X-ray diffraction,their thickness were measured by eddy flow thickness instrument.The hardness of pure magnesium,MAO coating,MAO/CrN duplex coating were measured by microhardness tester.The surface morphology and cross section morphology of coating were observed by scanning electron microscope(SEM).Using corrosion weight loss method and passivation curve test to study the coating’s corrosion-resistance property.The experiments for the friction and wear properties of MAO coating and MAO/CrN duplex were done in dry and 3.5%NaCl condition.The specific wear rates were calculated according to the data of the wear volumes.The friction coefficient and the wear rates,which were obtained through experiments,to evaluate the wear resistance of coatings.The results show that the MAO ceramic coating on pure magnesium is mainly composed of MgO,MgSiO3 and Mg,the maximum hardness of MAO coating is 736HV10.The corrosion loss of MAO coating is only a quarter of the pure magnesium,after micro-arc oxidation,the corrosion potential of sample increased from-1.69 V to-1.42 V,the corrosion current density reduced two orders of magnitude,the polarization resistance improved two orders of magnitude,the corrosion resistance of the sample was improved significantly.In air condition,with the increase of load and speed,the friction coefficient of MAO coating decreased,and its wear rates increased.In 3.5%NaCl solution,composed with the air condition,the MAO coating owns smaller friction coefficient and wear rates.The MAO/CrN duplex coating is mainly composed of MgO,MgSiO3,Mg,CrN,Cr,and Cr2N,its hardness reached to 1090HV10.After micro-arc oxidation and deposition of CrN by magnetron sputtering,the corrosion potential of the sample increased from-1.69V to-0.9V,the corrosion current density reduced three orders of magnitude,the polarization resistance improved two orders of magnitude,and the corrosion resistance of the duplex coating superior to single MAO coating,and the corrosion resistance of MAO/CrN duplex coating is superior to the signal MAO coating.In air condition,with the increase of load and speed,the friction coefficient of MAO/CrN duplex coating reduced to 0.37,its wear rate increased to 8.73×10-7mm3/Nmm.In 3.5%NaCl solution,the MAO/CrN duplex coating owns smaller friction coefficient and wear rate.Meanwhile,the wear resistance of MAO/CrN duplex coating is superior to the signal MAO coating.