Structure And Properties Of Nd-Doped Micro-Arc Oxidation And Its Composite Coatings On TC11 Titanium Alloy

Due to the high specific strength,and high temperature resistance,titanium alloy has become the material of choice for aerospace engines looking to improve their thrust-to-weight ratio.However,the low hardness,poor wear resistance and high oxygen potential energy easily reacts with oxygen,affecting engine performance and limiting titanium alloy’s deep application in the aerospace field.Based on the above problems,this paper prepares an oxide coating doped with rare-earth oxide particles on TC11 titanium alloy through the technique of micro-arc oxidation electrolyte,and uses this as the basis for the preparation of high-entropy alloy films by compound magnetron sputtering,in order to obtain a composite coating with excellent wear resistance and high-temperature oxidation resistance to enhance the application prospects of its titanium alloy in more complex environments.The scanning electron microscopy（SEM）was used to examine the surface morphologies of the micro-arc oxidation and composite coatings.the energy spectrum analysis of the micro-arc oxidation coating and composite coatings,as well as the X-ray diffraction（XRD）characterization of the composition of the micro-arc oxide and composite coatings.The high temperature oxidation experiments were carried out to investigate the high temperature oxidation resistance of the micro-arc oxide coating and the composite coating,and the following main conclusions were reached.（1）Micro-arc oxidation ceramic coating were prepared on titanium alloy using the micro-arc oxidation technique in electrolytes containing Nd₂O₃ concentrations of 0 g/L,1 g/L,2 g/L,and 3 g/L;the Nd content of the coating surface increased as the Nd₂O₃ concentration increased,and the main components of the micro-arc oxidation coating were Ti O₂ and Si O₂;the least wear weight loss was observed when Nd with the addition of Nd₂O₃ at 1 g/L,the minimum wear weight loss and minimum width of 598.04μm were observed.The wear resistance was improved to some extent when compared to the titanium alloy substrate and other added concentrations of the micro-arc oxidation coating;high temperature oxidation experiments showed that the oxidation weight gain of the substrate was 2.278 mg/cm²,and the minimum weight gain of the specimen after oxidation of the micro-arc oxidation coating with the addition of Nd₂O₃ concentration of1g/L was 0.139 mg/cm²,which obviously improved the TC11 substrate high temperature oxidation performance.（2）CoCrFeNi films were deposited on the microarc oxidation coating prepared by adding 1g/L Nd₂O₃ particles to obtain MAO/CoCrFeNi composite coatings.It was found that with the increase of sputtering time,the surface of the prepared composite coatings tended to be smooth and flat,and the number and diameter of micropores decreased.When the sputtering time was 6h,the width of high-temperature wear scar was the narrowest at room temperature and 400℃,which had good wear resistance;at 600℃,the composite coating had good high-temperature oxidation resistance,and the composite coating with sputtering time of 6 h at 727℃and 800℃had lower oxidation weight gain,which enhanced the high-temperature oxidation resistance of TC11.（3）The MAO/Al_0.3CoCrFeNi composite coating was obtained by depositing Al_0.3CoCrFeNi film on the microarc oxidation coating prepared by adding 1 g/L Nd₂O₃ particles.It was found that the surface coating of high-entropy alloy film mainly existed in FCC structure with uniform distribution of high-entropy alloy elements,and the surface of the prepared composite coating was smoother and flatter with the extension of sputtering time;when the sputtering time was 4 h,the wear width of the composite coating was smaller at room temperature and 400℃,and the wear resistance was better than that of the other composite coatings with sputtering time.The composite coatings with 4 h sputtering time have lower oxidation weight and relatively smaller oxide layer thickness after oxidation at 600℃,727℃and 800℃,and the high temperature oxidation resistance is better than other MAO/Al_0.3CoCrFeNi composite coatings and substrates with sputtering times.