Research On The High Temperature Deformation And Microstructure And Properties Of Ti-44Al-8Nb-0.2W-0.2B-0.5Y Alloy

Due to the advantages of low density,high specific strength,creep resistance and high temperature oxidation resistance,As a representative of high temperature and high strength structural material,Ti Al alloy has a bright future in the field of aerospace.With the addition of a large number of Nb elements with the high melting point,the difficulties in preparation of high Nb containing Ti Al alloy ingot and deformation resistance limits its processing and application.Through?phase solidification,hot isostatic pressing,homogenization annealing and other technological measures,the segregation and internal stress of castings can be reduced,and the defects of castings can be eliminated.Ti-44Al-8Nb-0.2W-0.2B-0.5Y(at.%)alloy ingot were prepared by vacuum consumable arc remelting.In this paper,the microstructure and properties of high Nb containing Ti Al alloy in as-cast,hot working process and heat treatment were studied.As-cast Ti-44Al-8Nb-0.2W-0.2B-0.5Y alloy is composed of a large number of large-sized?₂/?lamellas,?/B2 and a small amount of slip-shaped?phase at the grain boundary.There are a few bright white YAl₂ phases in the lamellae and grain boundaries.YAl₂ phase can refine the distance between grains and lamellae,reduce the activation energy of deformation and improve the hot working performance of as-cast alloy.The tensile strength of as-cast alloy is 538MPa at room temperature,and the elongation at room temperature is only 0.1%.As-cast Ti-44Al-8Nb-0.2W-0.2B-0.5Y alloy is forged in the?single phase region(1340?)and the?+?+?three phase region(1250?)respectively.The pancakes with 75%deformation was prepared,and furnace cooling and air cooling after forging were carried out respectively.The high Nb Ti Al alloy forged at 1340? has a nearly lamellar structure of?₂/?.?₂/?lamellae are transformed from deformed?grains.There are obvious forging streamlines in the air-cooled structure,which are mainly elongated lamellar structure.The cooling structure in the furnace is mainly composed of equiaxed lamellae,and the lamellae spacing becomes larger.In furnace cooling alloy,due to the transformation of parent phase?grain,the orientation of the same laths of alloy is different,and there is a Blackburn orientation relationship between them.The microstructure of as forged alloy at 1250? consists of?₂/?lamellae,?phase and equiaxed?grains.After forging in the three-phase region,the lamellae were bent and a large number of recrystallized?grains with grain size of about 5?m appeared in the grain boundary.The tensile strength of air-cooled and furnace cooled structures forged in?single-phase region(1340?)is lower than that forged in?+?+?three-phase region(1250?).When the forging process is the same,the tensile strength of alloy air-cooled structure is higher than that of furnace cooled structure.The tensile properties of forged Ti-44Al-8Nb-0.2W-0.2B-0.5Y alloy are closely related to temperature.With the increase of tensile temperature,the high temperature strength increases and plasticity of the alloy decreases.The high temperature strength of air-cooled and furnace cooled structures at 1340? is higher than that at 1250?.At 1310?/10min/FC,the full lamellar structure can be obtained,and the lamellar size is about 80?m.The duplex microstructure obtained by heat treatment at 1250?/2h consists of fine equiaxed?grains(8?m)and fine lamellae colony(18?m).At room temperature,the tensile strength of the fully lamellar structure obtained by air cooling at 1310?/10min is the highest,reaching 898mpa.After air cooling at 1250?/2h,the tensile strength of the duplex microstructure is the lowest,only 673MPa.The tensile strength of the fully lamellar and duplex microstructure obtained by furnace cooling at 1310? for 10 minutes and at 1250? for 2 hours were 830MPa and 851MPa,respectively.