Study On High Temperature Oxidation Corrosion Behavior And Mechanism Of Ti-based Nitride Coating

Titanium alloys are widely used in structural parts of aero-engines and gas turbines due to a series of advantages such as low density,high specific strength,good corrosion resistance and easy processing.With the rapid development of the defense industry,the service environment of military aircraft has moved from inland to ocean.The tropical marine environment such as the South China Sea is extremely harsh.The high temperature,high humidity,and high salt environment have caused serious corrosion problems in the compressor blades of aero engines and gas turbines during long-term service.Depositing protective coatings can improve the corrosion resistance and mechanical properties of titanium alloys.Therefore,it is of great significance to develop a protective coating system suitable for aero-engine compressor blades in marine environments.In this paper,the TiN coating,TiN/Ti coating,TiAlN coating and TiAlN/Ti coating were deposited on the surface of titanium alloy using Multi-arc Ion Plating technology.The corrosion behavior of the coating at room temperature in 3.5 wt.%NaCl solution and the corrosion behavior of high temperature oxidation and hot salt corrosion at 500? were studied.The main findings were as follows:(1)Different NaCl application methods have different effects on the corrosion behavior of the coating.A large area of peeling and cracks occurred on the TiN coating surface after salt spray and 500? high temperature synergistic corrosion for 2 h,mainly because in the salt spray environment,the inherent defects of the coating(holes,penetrating defects,etc.)provide a fast channel for the corrosive solution to penetrate into the coating.The internal TiN coating was corroded to form loose and porous corrosion products under high temperature environments.Theoretical calculation found that V_{(corrosion product volume)}>V_{(reactant volume)},the volume mismatch produces expansion stress and eventually causes the coating to peel off.The"Stress-chemical coupling"corrosion damage mechanism was proposed to reveal this failure behavior.(2)The coating structure was optimized,and the TiN/Ti multilayer coating was prepared by Multi-arc Ion Plating technology to reduce the number of inherent defects of the coating and reduce the NaCl solution permeability in the salt spray environment.The TiN coating and TiN/Ti coating were subjected to salt spray and 500? high temperature synergistic corrosion experiments.It is found that the corrosion resistance of TiN/Ti coating was better than TiN coating by the change trend of the corrosion kinetic curve.The TiN coating surface has a similar network-like corrosion morphology and internal corrosion mostly occurs at the grain boundary of the coating,which was caused by the structure of the TiN coating and the unique characteristics of the grain boundary.In the TiN/Ti coating,the selective corrosion was found that the Ti layer was severely corroded and the adjacent TiN layer remained intact,and the edge of the corroded area was abundantly enriched in Na.We believe that solid NaCl was used as an electrolyte to form a micro cell with the Ti layer and TiN layer during the hot corrosion process,and a verification experiment was designed to prove this phenomenon.(3)TiAlN coating and TiAlN/Ti coating were prepared by Multi-arc Ion Plating technology.The oxidation kinetic curve shown that the two coatings have good oxidation resistance and no obvious internal corrosion phenomenon in the coating after oxidation at 500? for 100 h,which effectively protects the alloy matrix.The salt spray corrosion performance of the two coatings at room temperature was evaluated by the potential polarization curve.The I_corr of the TiAlN/Ti coating was the smaller,indicating that the coating has better corrosion resistance.The selective corrosion similar to TiN/Ti coating was observed in TiAlN/Ti coating in salt spray and 500? high temperature synergistic corrosion,the difference was that the corrosion depth was significantly shallower.The main reason is that Al₂O₃ protective layer was formed on the surface of the TiAl-based coating,which improves the oxidation resistance and corrosion resistance of the coating.