High Temperature Oxidation Behaviors Of Ti₂AlNb Alloy With Surface Plasma Aluminized Layer

Ti₂AlNb orthorhombic alloy have exhibited great potential as elevated temperature structuralmaterial for advanced aerospace due to its high-yield strength, fracture toughness and creep resistanceas well as its low notch sensitivity. It has an important significance for reducing the vehicle weight,improving the fuel efficiency and high temperature service performance. But the shortage of poorhigh temperature oxidation resistance restricted its actual uses. To solve these problems, this paperproposed to form the aluminizing modification layer on Ti₂AlNb alloys by double glow plasmasurface metallurgy technique. The microstructure, chemical composition distribution and phaseconstituent of the layer was analyzed by SEM, EDS and XRD. The microhardness, tribologicalbehaviors, Corrosion behavior and high temperature oxidation behaviors of the layer wereinvestigated.The optimum process parameters of plasma aluminizing on Ti₂AlNb alloy are listed as follows:source voltage:650V, cathode voltage:450V, distance between source electrode and work-piece:10mm, working pressure:40Pa, diffusing time:3h. The aluminized layer is compact andhomogeneous and combined well with the substrate. The aluminized layer is about10μm thick andconsisted of an outer aluminum rich layer and inner Al-diffusing layer, the compositions of the layerdistributes in gradients from the surface to the substrate. The microhardness of the layer is440.2HV_0.1which is higher than the substrate’s. Ball-on-Disc rubbing tests show that the aluminized layerimproved the abrasion resistance of the substrate. Electrochemical tests show that the corrosionresistance of the layer and substrat are approximate. After oxidized at650℃,750℃,850℃for100hours, the oxidation films are compact and without flaws, and the aluminized layer gained lessoxidation mass. The substract’s oxidation products are TiO₂, AlNbO₄, and a little Al₂O₃. The oxidationfilms of aluminized layer are consisted of an outer Al₂O₃layer which may stop the diffusion ofoxygen and inner TiAl₃which may improve the risistance to high temperature oxidation. EDS resultsshowed that the oxygen is only existed within1μm of the oxidation layer which proved that thealuminized layer effectively prevent the internal diffusion of oxygen. The results show that theimprovement of high temperature oxidation resistance of Ti₂AlNb alloy is announced.