Preparation And Creep Mechanism Of Ti₅Si₃/TiAl Composite

TiAl alloy has high elastic modulus,low density and good creep resistance,so it has a wide application prospect in aerospace field.With the increase of service temperature,the creep resistance of TiAl alloy is insufficient,and the relationship between strength and creep resistance is opposite,which seriously impeded its application development.Based on the above questions.In this paper,the whole lamellar Ti₅Si₃/TiAl composites with reinforced phase content of3.5vol.%were successfully prepared by pressure impregnation combined with hot pressing sintering and lamellar heat treatment.First,scanning electron microscopy(SEM)was used to investigate the microstructure changes during the preparation and heat treatment of Ti₅Si₃/TiAl composites.Then,the tensile properties of Ti₅Si₃/TiAl composites were evaluated at room temperature and high temperature.The creep behavior and deformation mechanism of Ti₅Si₃/TiAl composites were investigated.At 800?and 20MPa,a reaction layer of about 6?m is formed on the surface of the Ti sphere.At 1250?,?₂+?lamellar structure and Ti₅Si₃ particles precipitate in the sintered material.After sintering at 1350?,the material is basically compact,the matrix structure is near lamellar,and the Ti₅Si₃ particles are distributed around the lamellar cluster and inside the lamellar structure.The tensile test data and fracture morphology at 730?830?show that the fracture is mainly brittle fracture.The yield strength and tensile strength of the material at780?are the highest,which are 703MPa and 591MPa,respectively.The results of creep tests at 250MPa and 700?show that the steady-state creep rate at 780?is 30 times that at 700?.With the increase of temperature,the steady-state creep rate increases significantly,and the creep resistance near lamellar microstructure is poor at high temperature.The whole lamellar Ti₅Si₃/TiAl composite was obtained by heat treatment at1400?for 20min.The whole lamellar Ti₅Si₃/TiAl composite was composed of?₂/?.The grain boundaries of the lamellar Ti₅Si₃/TiAl composite were serrated.The tensile test data and fracture morphology at 730?800?show that the material is mainly brittle fracture.The tensile strength and yield strength at 780?are the highest,reaching 597MPa and 533MPa,respectively.Compared with the lamellar composite,the strength decreases slightly.The creep test results at 700?800?and 250MPa show that the steady-state creep rate at 780?is 4 times that at 700?.The creep test results at 750?and 150?250MPa show that the steady-state creep rate of 250MPa is 1.8 times that of 150MPa.With the increase of creep temperature and stress,the steady creep rate increases slowly,and the high temperature creep resistance of the whole lamellar structure is good.During the creep process at 250MPa and 700?800?,the lamellar microstructure spheroidizes,?₂??.At 750?,a large number of dislocations appear in?lath,resulting in twins.The creep deformation mechanism is dislocation slip and twinning.At 800?and 250MPa,dislocation appears in?₂strip,and the creep deformation mechanism is mainly dislocation slip.