melted in a laboratory arc furnace from pure components (~99.9 wt.%) are studied by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), differential thermal analysis (DTA), and compression testing. The alloys are found to consist mainly of a superfine lamellar structure of decomposition β → α → α + γ → α 2 + γ and contain tiny islands of the γ phase and also the β phase at 12 at.% Nb or Ta. The CALPHAD approach is used to obtain a thermodynamic description of the Al−Nb−Ta−Ti system, which adequately reproduces the experimental data. The compression tests performed at room temperature show that the ternary alloys with 45 at.% Al are characterized by higher strength but lower plasticity than the alloys with 47 at.% Al. For the Ti 46 Nb 8 Al 46 and Ti 46 Ta 8 Al 46 alloys, high strength in the temperature range 20−800°C and a drop in plasticity to 2−4% at 200−600°C are revealed. Among the quaternary alloys examined, the best combination of strength and plasticity (σ 02 = 1043 MPa, σ ult = 1612 MPa, ε pl = 12.4%) is exhibited by the Ti 47 Nb 4 Ta 4 Al 45 alloy.
The temperature and velocity sensitivity of the mechanical properties of TiAl-based alloys were investigated. The structure was determined by scanning electron microscopy in SEI mode. Mechanical properties were determined by the results of tensile and bending tests. It was found that the temperature and velocity dependence of the mechanical properties in alloys with 47% Al is practically absent. This makes them promising for use as structural materials, due to the stability of their properties.
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