Hot Deformation And Creep Behavior Of Network Ti₅Si₃/TiAl Composites

Due to the low density,high specific strength,TiAl alloy can significantly improve thrust-weight ratio.It is expected to be aerospace ideal material of leap-forward development for the future.Applied mostly for high temperature parts,creep property is a key factor for the safe use of the material.The addition of Ti 5Si3 particles is conducive to further enhance the high temperature strength,oxidation resistance and creep resistance.In this paper,network distributed Ti₅Si₃/TiAl composites with different content?1.2%?3.5%?6.9%?of reinforcement and TiAl material without reinforcement respectively were manufactured by pressure infiltration and hot-pressure sintering in order to perform better creep properties.The hot deformation behavior of composites were investigated to overcome the shortcoming of hot working.OM,SEM,TEM and XRD were utilized to observe and analyze the microstructure of the composites.And determination of density,hardness and tensile p roperties was conducted.The thermal simulation test and creep test of composites were conducted for the study of the thermal deformation and creep behaviors.6.9vol.%Ti₅Si₃/TiAl composite and 3.5vol.%Ti₅Si₃/TiAl composite were distributed by double quasi continuous networks,and 1.2vol.%Ti₅Si₃/TiAl reinforced composite material was distributed along the grain boundary,while pure TiAl material was composed of equiaxial ? phase and lamella microstucture.Along with the increase Ti₅Si₃,microhardness increased at room temperature.High temperature tensile test indicated that ductile to brittle transition temperature of the composite was between 800⁸30?.3.5vol.%Ti₅Si₃/TiAl composite performed best yield strength at high temperatures up to 399.2MPa at 800?.And the elongation at 850? was 25.5%.The hot compression deformation results indicated that flow-stress of composites increased as increasing strain rate and as reducing temperature.Compared with 3.5vol.%Ti₅Si₃/ TiAl composite,6.9vol.%Ti₅Si₃/TiAl composite performed higher compressive strength at elevated temperature.But 3.5vol.%Ti₅Si₃/TiAl composite possessed better potential in hot working at lower temperature.Under the condition of 1000¹200? and 0.001¹s-1,Thermal deformation activation of 3.5vol.%Ti₅Si₃/TiAl composite was 564.67 k J/mol,and corresponding thermal deformation constitutive equation was acquired.Hot working diagram of strain of 0.2?0.3?0.4 and 0.5 showed that the following areas above 1125? and the under strain rate of 0.01s-1 were ideal hot working conditions for 3.5%Ti₅Si₃/TiAl composite.In addition,Along with the increase of temperature and the decrease of strain rate,it was advantageous to the dynamic recrystallization and grain growth.The existence of the Ti₅Si₃ particle was helpful to accelerate the rate of dynamic recrystallization,but it would limit grain growth.3.5vol% Ti₅Si₃/TiAl composite performed the highest creep properties under the same creep test condition.Too much Reinforcing Ti₅Si₃ would accelerate the decomposition of lamella microstructure to reduce the creep properties of the material.For 3.5vol% Ti₅Si₃/TiAl material,improving of temperature and load stress would result in increasing of steady creep rate.Stress played a leading role on creep deformation at low temperature,while temperature played a dominant role at high temperature.Under the condition of 700⁷75? and 150²25MPa the test creep constitutive equation could be described as e?5?=0.545???2.60exp?-259122/RT?.TEM observation indicated that microscopic deformation structure of 3.5vol.%Ti₅Si₃/TiAl composite under 750? and 225 MPa was intensive dislocations in ? grain slipping,and creep stress index n value was 2.91.While Under 750? and 250 MPa microscopic deformation structure was {111} deformation twin.It?s main deformation mechanism was accomplishing orientation adjustment by twinning,and creep stress index was 11.17.