Effect Of Alloying On The Microstructure And Mechanical Properties Of Ti-48Al-2Cr-2Nb Alloys

TiAl based alloys are perspective to be used in the areonautic and astronautic field as high temperature structure material due to their low-density, high strength, high creep resistance and high oxidation resistance. However, the alloys normally have low plasticity and their microstructures are hard to be controlled. In light of it, in this thesis, the Ti-48Al-2Cr-2Nb alloy(Ti4822) was taken as the research object, and the effects of the alloying elements( Si、Zr、Mn、Mo) on the microstructure and mechanical properties of Ti-48Al-2Cr-2Nb alloy were investigated, and the alloying elements were optimized. Moreover, The effects of Si content on microstructures and mechanical properties on the Ti-48Al-2Cr-2Nb alloy was studied, and the microstructure of the alloy containing Si alloy was optimized by heat treatment. The main results are as follows:1. The alloys of Ti-48Al-2Cr-2Nb-0.6x( x=0、Si、Zr、Mo、Mn) were prepared by vacuum arc melting method, and effects of the additions on the microstructures, including grain size, spacing of the lamella and precipitated phase, and mechanical properties of the alloy were investigated. The results indicate that the addition of Si、Zr、Mo、Mn can refine the microstructure of the alloy, change the lattice parameters of ? phase and the volume fraction of phase constitution. Si addition to the alloy has an significant influence on the microstructure and properties..2. The alloys of Ti-48Al-2Cr-2Nb-x Si( x=0、0.2、0.4、0.6) were by vacuum arc melting method, and the effects of the addition Si on the grain size, spacing the lamella, precipitated phrase and the lattice parameters of γ-TiAl were investigated. It is found that Si addition can refine the microstructure, and decrease the c/a ratio, which are favor to the improvement of the plasticity of the alloy.3. The Ti-48Al-2Cr-2Nb-0.4Si was solution treated at 1310°C, 1350°C and 1370°C, respectively, and the impacts of the heat treatment on the constitution of phases, the morphologies of grain boundary, distribution of the precipitates and the mechanical properties were investigated. The results indicate that the microstructure of Ti-48Al-2Cr-2Nb-0.4Si alloy treated at 1350°C exhibits a fully lamellar structure with fine grains. The alloy exhibits a good comprehensive property with IPF value to 2008.2, which increased by 50% compare with the as-cast Ti-48Al-2Cr-2Nb-0.4Si alloy.