Pressure Infiltration And Creep Behavior Of Ti₅Si₃/TiAl Composite

With the development of the aerospace field,it has brought higher requirements for high-temperature structural material.TiAl-based alloys become a potential hightemperature structural material because of its high specific strength,good creep properties and oxidation resistance.It can improve the high temperature strength as well as creep resistance of the TiAl-based alloys with the addition of Ti₅Si₃.In this study,full lamellar Ti₅Si₃/TiAl composites with different volume fractions were prepared by pressure infiltration and hot-pressure sintering in order to get better creep properties.Influence of temperature and the shape of the powder particles have been investigated by both experiment and finite element simulation.The microstructure of the composites have been observed and analyzed.And determination of density,hardness and tensile properties was conducted.The creep test of composites were conducted for the study of the creep behaviors and creep mechanisms.With the increase of infiltration temperature,the fluidity of Al-Si alloy is better,and the density of composite material is higher.So 800? was chosen as the best temperature for pressure infiltration.The phase composition of Ti₅Si₃/TiAl composites prepared by spherical titanium powder are Ti,TiAl and TiAl3,which means the reaction is not complete,while the phase composition of Ti₅Si₃/TiAl composites prepared by irregular titanium powder are TiAl and Ti3 Al.CFD simulations were used to investigate the fluid flow during the infiltration process.The result shows that the liquid Al-Si alloy has the smallest flow velocity in the spherical particles,while the largest in the cube particles.The flow velocity can increase with the increase of temperature.The full lamellar Ti₅Si₃/TiAl composites prepared by pressure infiltration have good density.The Ti₅Si₃ reinforcements distributed along the boundary as a continuous network.Along with the increase of Ti₅Si₃,hardness increased from HRC30.6 to HRC46.5.High temperature tensile test indicated that the temperatures of BDTC are determined to be 800-850?.At 800?,3.5vol.%Ti₅Si₃/TiAl composites performed best tensile strength and yield strength,up to 507.6MPa and 410.2MPa respectively.The fracture mode of the composite is translamella and become toughness fracture at 850? mixing with various fracture characteristics.Creep experiments were conducted on Ti₅Si₃/TiAl composites at temperatures of 700-775? and stresses from 150 to 225 MPa.Results show that the addition of Ti₅Si₃ can increase the creep resistance.For 3.5vol.% Ti₅Si₃/TiAl composites,the creep constitutive equation could be described as ???=0.894?2.14exp?-264375/RT?under the condition of 700-775? and 150-225 MPa.It was found that ?2/? lamellar would transform to single ? during creep process,which means phase transformation of ?2 ?? occurred.At lower temperatures?700??,the stress exponent n is between 1-2 and the creep mechanism is dislocation gliding;At higher temperatures?775??or at a higher applied stresses?225MPa?,the stress exponent n is between 7-10,the creep mechanism is dislocation climbing and deformation twinning.