| With rapid development of Aeronautics and Astronautics industry,the demand of spacecraft is increasing,and the request of manufacturing material is rigorous,too.Since 1950s,it is commonly believed that the titanium is positive to improve the performance of Aeronautics and Astronautics engines because of the excellent chemical stability and higher specific strength.But the complex working environment of aircraft has limited the application area of titanium alloy.At the work condition higher than 500?,titanium alloy will fail because the oxidation film on the surface of titanium is vulnerable and prone to further oxidized and may cause the damage of aircraft.High temperature titanium alloy has become important propulsion to explore universe.The fundamental method to improve the high-temperature oxidation resistance of titanium is alloying,and the defects are expensive research cost and endless research period.Compared with that,surface treatment offer some unique properties like lower cost,various methods,processing controlled,has been a hot area of research.The double glow plasma surface alloying technique which provides a new method to improve the high-temperature oxidation resistance of titanium because some unique advantages.This dissertation designed high-temperature oxidation resistance coatings by double glow plasma alloying method,and studied the surface morphology,composition and mechanical property prepared at different temperature and transition layer,then explored the high-temperature oxidation resistance and electrochemical performance of different samples.The mainly research results are as follows:?1?TC4-Mo-Ir and TC4-Ni-Ir modified coatings was successfully fabricated on Ti6Al4V substrate by double glow plasma alloying method.After treatment,the surface roughness of treated samples were improved and the surface morphology show rugged mound shape.The mainly composition of alloying coatings were polycrystalline iridium with?111?,and?220?crystal plane from EDS and XRD consequences.The composition of transition layer was spreading and the thickness of layers and surface roughness were increase with higher working temperature.?2?The surface hardness of treated TC4-Mo-Ir and TC4-Ni-Ir samples were improved,but the value of Vickers microhardness was different if the load was disparate,both hardness value of TC4-Mo-Ir and TC4-Ni-Ir samples were stabilise at 600830 HV.The nanoindentation test was also prove that the hardness and elasticity modulus of treated samples were increased.The highest hardness of coatings was 13.51 Gpa and the elasticity modulus of coatings were stabilise at 205 Gpa.?3?After oxidation 100 hours at 900?,the surface of TC4 substrate was oxidized and peel off,XRD results prove that the surface of substrate was oxidized completely while the surface morphology of TC4-Ni-Ir was intact,the oxidation increase was lower than substrate obviously,provide better high-temperature resistance.The barrier effect of Mo-Ir coatings was weaker than Ni-Ir coatings.Both coatings prepared at 900?prove best high-temperature resistance and the mainly oxidation products were IrO2.?4?The corrosion resistance test was proceed at 3.5%NaCl solution by electrochemical workstation and the results of polarization curves show that the corrosion resistance of treated samples were improved obviously and the samples is of best behavior at a 900?.The self-electric potential of samples prepared in 900?was improved to 0.58×10-1 V,higher than-2.71×10-1 V of substrate,the corrosion current density of substrate was 5.02×10-7 A/cm2 while the corrosion current density of treated samples was decreased to 7.44×10-8A/cm2.The electrochemical impedance spectroscopy of treated TC4-Mo-Ir samples were higher than TC4 substrate;Corrosion resistance of TC4-Ni-Ir samples prepared by double glow plasma technology at 900?was better than TC4-Mo-Ir samples,the self-corrosion potential were 0.79×10-1 V,the corrosion current density were decrease to 2.06×10-8 A/cm2.After treatment by double glow plasma technology,the resistance of treated samples were improve and the lowest corrosion rate was 0.26×10-3 mm/a. |
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