Study On High Temperature Deformation Characteristics Of TiAl Alloy Sintered By Spark Plasma Sintering

Ti Al alloy is a new type of lightweight and high temperature structural material with high application value due to its advantages such as low density,high specific stiffness,high specific strength,and good creep resistance.As a lightweight material for hot-end parts such as aerospace engine blades,it has broad application prospects.However,its application has been limited in industry due to its intrinsic brittleness,low ductility,and poor formability.In order to overcome these shortcomings,this paper uses the spark plasma sintering process to densify the high-purity and low-oxygen spherical aerosolized Ti Al pre-alloyed powder.The microstructure and properties of the Ti Al alloy sintered body are systematically studied.The hot deformation behavior lays the foundation for the preparation of large-sized Ti Al alloy sheet by powder metallurgy.Using the Ti-43.5Al-5Nb-1V-1Y?at.%?pre-alloy powder prepared by gas atomization process as the raw material,the dense Ti Al alloy was successfully prepared by the spark plasma sintering process with different sintering temperatures.At sintering temperatures of 1200?,1250?,and 1300?,near-gamma microstructure,duplex microstructure,and nearly lamellar microstructure were obtained.The phase compositions were all?-Ti Al,?₂-Ti₃Al,and YAl₂.When the sintering temperature is 1250?,the structure is uniform,the density is high.Its breaking strength is 2118.7 MPa,which is similar to that of the alloy with sintering temperature of 1300?,about 20 MPa higher than that of the alloy with sintering temperature of 1200?,and its plastic deformation is 24.31%.The grain size of the alloy with sintering temperature of 1300?is larger than that of sintering temperature of 1250?.In the room temperature compression experiments,the fracture modes of the alloys with sintering temperatures of 1200?and 1250?are mainly intergranular fracture,while the fracture modes of alloys fabricated at1300?are intergranular fracture and transcrystalline fracture.The isothermal thermal simulation compression experiment was performed on a Ti Al alloy with sintering temperature of 1250?by the Gleeble-1500D thermophysics simulation experiment machine to analyze its thermal deformation behavior.The experimental parameters are deformation temperature of 1050?-1200?,strain rate of 0.001 s^-1-1 s^-1,and deformation of 50%.The experimental results show that the flow stress of Ti Al alloy sintered by spark plasma sintering is sensitive to the deformation temperature and the strain rate,and the peak flow stress decreases with the increase of the deformation temperature and the decrease of the strain rate.The rheological behavior of the Ti Al alloy during hot compression deformation can be described by the Zener-Hollomon parameter including the Arrhenius term.The peak stress constitutive equation of the sintered Ti Al alloy at high temperature is obtained.The activation energy Q value of the hot deformation is calculated as 267.196 k J/mol.The empirical calculation of the equation can better describe the deformation characteristics of the alloy.The main softening mechanism of high temperature plastic deformation of Ti Al alloy is dynamic recrystallization?DRX?.DRX is observed under all deformation conditions.The grain size of dynamic recrystallization decreases with the increase of Zener-Hollomon?Z?parameter value.Based on the dynamic material model,a hot working diagram of Ti Al alloy with a true strain of 0.5 is constructed.The temperature of 1090?-1200?and the strain rate of 0.0067 s^-1-0.08 s^-1 are ideal areas for thermal deformation of Ti Al alloy,which is suitable for hot working.The main instability of Ti Al alloy is cracking.The best hot working process should be selected to avoid the instability area to ensure the quality of the processed parts.