Research On Casting Properties Of TiAl8Nb Alloy

With the development of aerospace and military industries,traditional nickel-based and iron-based high-temperature metal materials are increasingly unsuitable for current development,and new materials are urgently needed to meet the increasing demand.High niobium titanium aluminum alloy is a model of high temperature and high strength TiAl alloy.It can still maintain excellent mechanical properties at high temperature.It can fully meet the requirements of use even in the extremely demanding service conditions such as aviation,aerospace and military fields.Both the development and application of advanced equipment in the high-tech field and the research and development of automotive components are based on the development of high-temperature structural materials.Although the application prospects are extremely broad,the production of titanium-aluminum-based alloys is difficult,the cost is high,and the machining is difficult.The actual application is greatly restricted,and mass production and promotion are also hindered.In this paper,first select basic zirconium carbonate,glacial acetic acid and ethanol to prepare zirconium sol,and study the reaction temperature and reaction time and the basic zirconium carbonate and glacial acetic acid ratio on the formation and viscosity of zirconium sol;then use this zirconium sol Prepare the surface layer slurry for raw materials and zirconia,and study the change rule of the surface layer viscosity with powder-liquid ratio and stirring time;further study the oxide for investment casting from the aspects of avoiding cracking of the mold shell and roasting process Preparation process of ceramic mold shell;finally,four high-niobium titanium aluminum alloys Ti-36.3Al-8Nb,Ti-39.1Al-8Nb,Ti-41.9Al-8Nb and Ti-46Al-8Nb are centrifugally poured using a vacuum suspension melting furnace casting.Analyze the macro defects of the casting,then observe the microstructure,and analyze the effect of Al content on the structure of the high-niobium titanium aluminum alloy in combination with the phase diagram.The results of the study showed that with the increase of the ratio of basic zirconium carbonate and glacial acetic acid,the increase of the reaction temperature and the extension of the reaction time,the viscosity of the obtained zirconium sol decreased,and the zirconium sol became clearer and more transparent.The zirconium sol has a single component and can be stable at high temperatures;the surface slurry prepared by the zirconium sol and zirconia powder gradually increases in viscosity as the powder-liquid ratio increases,and the viscosity decreases slightly with the extension of the stirring time.After increasing.Cracking is easy to occur during the dewaxing of the mold shell,and the present problem can be effectively solved by using the method of combining the hollow wax mold and the hot sand dewaxing.The actual casting of the exhaust valve casting has good reproducibility,the surface is smooth and bright,but there are still defects,such as insufficient pouring at the edge of the exhaust valve disc and the thin-walled position;it also appears inside the exhaust valve Shrinkage,shrinkage and other defects;Ti-36.3Al-8Nb,Ti-39.1Al-8Nb,Ti-41.9Al-8Nb and Ti-46Al-8Nb,although the Al content is different,but mainly by?₂-Ti3Al and?-TiAl two-phase composition,when the Al content is low,the alloy structure mostly exists in laths and dendrites.When the Al content is high,the?₂/?lamellar structure can be clearly seen and exist on the lamellar layer There is obvious white network?segregation.With the increase of Al content,the layer transformation is more complete,and the white network?segregation is also significantly reduced.