Study On Microstructure And Mechanical Properties Of Ti-Al-Fe Based Alloys

The ?+? titanium alloys are applicable for the aeronautical structural parts because of its good comprehensive performance and processing performance,of which the Ti-6Al-4V(TC4)is a typical representative.It is the most widely used titanium alloys at present.The Ti-6Al-4Fe alloy developed based on TC4 has excellent comprehensive properties,and this alloy system has the potential to be further excavated.In this dissertation,the Ti-Al-Fe alloys are used as a research object.And in the designed Ti-xAl-yFe(x=4,5,6;x+y=10)series alloys,the Ti-6Al-4Fe alloy shows greater advantages and development potential compared with the other two alloys.The microstructure and mechanical properties of the as-cast and hot-rolled Ti-6Al-4Fe alloys with a small amount of elements(C,B,Si)are studied.The alloys are prepared by vacuum non-consumable melting equipment.And the mechanical properties of the alloys were tested by INSTRON-5982 universal-testing machine.The structure,microstructure,phase composition and fracture morphology of the alloys were analyzed by optical metallographic microscope,scanning electron microscope,transmission electron microscope and X ray diffractometer.The addition of B element into the as-cast Ti-6Al-4Fe-xB(x=0,0.19,0.37,0.74)series alloys will form rod-shaped TiB phase in the matrix.Adding with 0.05 wt.% B can significantly increase the compressive plastic strain,which from 14.20% to 20.90%.The yield strength increased and the compression strain reduced of Ti-6Al-4Fe-xB series alloys with the increase of B element content.The tensile mechanical properties at room temperature of the water quenched Ti-6Al-4Fe-xB series alloys which rolling at 850? were measured.It is found that the tensile strength of the Ti-6Al-4Fe-xB series alloys increased and the plasticity decreased with the increase of B element content.Tensile strength increased from 1106 MPa of Ti-6Al-4Fe alloys to 1350 MPa of Ti-6Al-4Fe-0.74 B alloys,and the plastic strain decreased from 14.78% of Ti-6Al-4Fe alloy to 6% of Ti-6Al-4Fe-0.74 B alloy.The tensile mechanical properties of the Ti-6Al-4Fe-xSi(x=0,0.25,0.5,1)series alloys which were rolled at 850 ? and cooled by water were measured at room temperature.The results show that the yield strength and ultimate strength of Ti-6Al-4Fe alloys with a small amount of Si element increase obviously.However,the ductility of the alloys decreases slowly with the increase of Si content.A series of Ti-6Al-4Fe-0.03C-xSi(x=0,0.25,0.5,1)alloys were obtained by adding a certain amount of C element into the Ti-6Al-4Fe-xSi series alloys.The results show that the plastic strain of the all alloys can be increased by adding C element but not at the cost of decreasing the yield strength and ultimate strength of the alloys.The yield strength and ultimate strength of the Ti-6Al-4Fe-0.03C-1Si are 1272 MPa and 1355 MPa,respectively,and the plastic strain of the alloy is 14.03%,which is equivalent to that of Ti-6Al-4Fe alloy,but the strength was increased by about 250 MPa.