Study Of Fabrication And Properties Of High Temperature Self-lubrication TiAl-based Alloys

A new light tribological material was created firstly by adding eutectic CaF₂-BaF₂ into TiAl alloys. Using this material, the dynamic properties of high speed fricition pairs were improved significantly.By adding eutectic CaF₂-BaF₂ into TiAl matrix, A new type TiAl-based high-temperature self-lubricating alloy was fabricated successly. The structural characteristics, physical properties and tribological properties were studied systemtically.An optimal sintering procedure for making the TiAl matrix self-lubricating materials is determined to be as follows: sinter temperature, 1200℃; soaking time, 30min and sintering pressure,30MPa. The resulting material exhibits high bending strength and fracture toughness, which are contributed to the Orowan dislocation reinforcement.It is shown that the main phases of the TiAl high-temperature self-lubricating alloy areγ-TiAl andα₂-Ti₃Al. In the center of the particles,α-Ti phase in rich of Al is found. The microstructure of the phases is influenced by the sintering temperature. An island-shape structure is observed when the temperature is raised to 1200℃. In the meantime time, some inerratic grains and twin crystals are formed. The microstructure is made up of layer and flake crystal groups ofα₂/γandγgrains with sizes of 50-100μm and 10-40μm, respectively. And the batten thickness of theα₂/γgroups is larger.The oxidation-resistance of the alloy was tested to characterize their reliability under high temperature circumstance. It is found that the oxidation kinetics of Ti-48Al-2Nb-2C (TANC) self-lubricating materials is influenced by the additions of the lubricants. A parabola shape kinetic curve is shown when 5% solid lubricant is added, indicating the improvement oxidation-resistance of the alloy. This is resulted form the fact that the solid lubricant blocks the channels for oxygen diffusion. However, a higher addition of the solid lubricant led to a decrease in oxidation-resistance.Finally, high temperature wearing tests were carried out to study the mechanism of self-lubricating materials with different solid lubricants. The lowest wearing rate is shown for the self-lubricating material with an addition of 10% solid lubricant, which is due to the formation of an intact film on the wearing surface.