Study On Microstructure,Properties And High Temperature Tensile Fracture Behavior Of TiAl Composite Sheet With Pore Distribution

With its low density,high strength and good oxidation resistance,TiAl alloy has become a promising high temperature structural material recognized by scholars all over the world.However,the alloy still has many problems,for instance,its high-temperature strength and room temperature toughness are relatively low,it is difficult to prepare and shape the plates,the cost is high and the prepared materials cannot meet the higher requirements of the high temperature structural parts in the service environment.In this paper,Al-2Si alloy foil and pure Ti foil were prepared into two kinds of layered composite sheets with different void sizes by means of vacuum hot pressing,low temperature heat treatment and parameter adjustment of high temperature heat treatment.Room temperature fracture toughness test and high temperature tensile performance test were carried out for the two composite sheets.Through scanning electron microscopy(SEM),X-ray diffraction(XRD),electron backscatter diffraction(EBSD)and other characterization methods,the microstructure evolution law of the composite sheets in the process of hot pressing and heat treatment the room temperature and high temperature fracture behavior were systematically studied,and the strengthening principle of the unique void layered structure on the mechanical properties of composite sheets was explored.Al-2Si alloy foil and pure Ti foil were combined by hot pressing at 525?/10^-2Pa/23 MPa/2.5 h,and then the composite sheet was heat-treated at low temperature under the condition of 660?/3 h-680?/7 h.Finally,the composite plate was subjected to high temperature heat treatment of 1250?/3 h+1320?/15 min/3 MPa(or 5 MPa)and two kinds of void layered TiAl with densities of 3.142 g/cm³ and 3.750 g/cm³ were successfully prepared.The composite plate is alternately arranged with equiaxed crystal structure and lamellar structure,and the voids are located in the middle of the equiaxed crystal layer.Most of the in-situ Ti₅Si₃ is dispersed in the composite sheet in the form of particles.The voids layered TiAl composite sheet prepared by high temperature heat treatment at 1250?/3 h+1320?/15 min/3 MPa had the highest elongation,11%and33.8%at 800?and 850?respectively,and the corresponding tensile strength was462 MPa and 384 MPa respectively.The fracture toughness in AO and DO modes was11.4 MPa?m^1/2 and 9.6 MPa?m^1/2 respectively.The voids layered TiAl composite sheet prepared by high temperature heat treatment at 1250?/3 h+1320?/15 min/5 MPa had the highest fracture toughness,respectively 15.0 MPa?m^1/2 and 13.1 MPa?m^1/2 in AO and DO modes.Besides,it had the highest tensile strength,respectively 565.4 MPa and 468.3 MPa at 800?and 850?,and the corresponding elongation is 6.3%and31.4%respectively,The main reasons for the perfect combination of strength and plasticity of the composite sheets are that the in-situ Ti₅Si₃ particles can limit the growth of the grains to refine the structure and the existence of pores,and layered structures can weaken the local stress and strain.