| Performances of Ti Al-based alloys are characterized by the combination of thegreat plasticity of metal and the high temperature strength of ceramic. Meanwhile, the density of Ti Al-based alloys is less than 4.5kg/cm3. They have higher high temperature strength,excellent oxidation resistance at very high temperatures and good corrosion resistance than traditional high-temperature alloys and are widely used in aerospace, automobile and petraleum fields. Whereas, its room temperature brittleness and poor processing performance seriously limit its development. So it is believed that the successful processing of intermetallic compound and the preparation of high-performance component with uniform structure and high density can not only promote wide applications of Ti Al-based alloys in the aviation field, but also provide a new way and thought for the research and development of advanced materials.In this paper, γ-Ti Al and α2-Ti3 Al double phases structure with equiaxed ultrafine grains in the Ti-45Al-x Nb(x=8、10、12) alloy was prepared by high-energy ball milling and vacuum sintering, and the characteristics of true stress and strain as well as the structure evolution law of the compressed alloy sample was investigated. Furthermore, the mismatch structure, interface binding orientation relationship and optimal orientation of the alloy sample after hot compression were carefully analyzed by HREM. The results showed that:(1) The particle size of powder of Ti-45Al-x Nb(x=8 、 10 、 12) was refined to nanometer by 25 h high-energy ball milling. With the increase of Nb content, the refinement effect is more obvious, which shows that the Nb element can improve the strength of powder refinement. The alloy powder generates Ti3Al、Ti Al3 and Ti3Al5 new phases during the refinement process.(2) The microstructure of the γ-Ti Al and α2-Ti3 Al duplex alloy in the Ti-45Al-x Nb(x=8、10、12) prepared by high-energy ball milling and vacuum hot pressing sintering method is ultrafine, and the grain size is within 100~200nm.The density of Ti-45Al-8Nb was 90.93%.(3) The alloy is sensitive to temperature and strain rate, and the peak flow stress is smaller at higher deformation temperature and with slower strain rate. In comparison to three alloys, the flow stress of Ti-45Al-10 Nb is the maximum and it has stronger work hardening ability than other two kinds of powders including Ti-45Al-12 Nb with the minimun flow stress.(4) Ti-45Al-12 Nb alloy strain sensitive coefficient m is 0.61 and the high temperature deformation activation energy Q is 496 k J·mol-1 at the temperature of1100-1200℃(0.01-0.0001s-1). The constitutive equation for the high temperature thermal deformation of ultrafine grained Ti Al alloy prepared by powder metallurgy(mechanical ball milling and vacuum hot pressing sintering) was established:34.54 1.65ε0.039)[sinh( ?] ex(-(28)496000 RTe)p /.(5) After high-temperature deformation, the grains of Ti-45Al-8Nb alloy are deformed by dislocation slip and twinning, and some dislocations can be found at the grain boundaries. And during high-temperature deformation, ultrafine equiaxed γ/γ, α2/γ andα2/α2 interfaces are different from the interfaces of lamellar γ-Ti Al and α2-Ti3 Al dual phase alloy. The γ/γ interface is easier to form twin structure under compression, whereas the α2/γand α2/α2 interfaces are prone to forming dislocation structure of superlattice. It is found that large-angle grain boundaries exist at(7) 1110(8)α2/(7)111(8)γ and( 1220)α2/( 1220)α2 interfaces. |
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