Research On Microstructure And Mechanical Properties Of Ti₂AlNb-Based Alloy Fabricated By Multiple Isothermal Forging

Ti₂AlNb-based alloys were competitive high-temperature engineering materialsdue to their attractive mechanical properties at elevated temperature. It has thepotential for replaceing nickel-base materials to fabricate the future jet enginecomponents. However, the poor elevated workability and low room temperaturedutility of as-cast and HIPed Ti₂AlNb-based alloys due to the coarse microstructurelimited its development.In the present work, Ti₂AlNb-based alloy ingots were prepared by inductionskull melting and vacuum self-consuming arc melting, the as-cast ingots undergo hotisostatic pressing （HIP） subsequently. To refine the coarse microstructure andimprove hot workability of HIPed alloys, multiple isothermal forging and multi-stephot pack rolling were performed. The main research contents of this study includedthe high-temperature deformation mechanisms of HIPed Ti₂AlNb-based alloys,microstructural evolution and mechanical properties during hot-working process.The average size of the HIPed orthorhombic titanium alloys is about2-4μm, alarge amount of α2and O laths have precipitated in coarse B2matrix, and the hotworkabilitiy of HIPed alloys was very poor, its elogation was merely53.74%whendeformed at950°C、1×10-3s-1. After three-step isothermal forging, the equiaxedmicrostructure with a finer grain size was observed. And, the elogation of the as-forged alloy reached651.6%when deformed at850°C、8×10-4s-1, so the hot-workability was increased notably. Superplastic behavior of the as-forged alloy intemperature range750-900°C was studied, and activation energy was295kJ/mol,suggesting that the low-temperature superplasticity mechanisms of this alloys wasgrain boundary sliding （GBS） with dislocation creep. The mechanical properties atroom temperature was also desirable, the yield and ultimate strength can reach to1233MPa and1234MPa respectively, and elongations up to3.8%was also obtained.In this paper, strong β stablizing elements such as Mo、Fe、V were used toreplace a part of Nb in Ti-Al-Nb alloys, and a intermetallic compound with nominalcompositions Ti-22Al-14（Nb,Mo,Fe,V,Si） was also prduced by induction skullmelting, subsequent hot isostatic pressing, multiple isothermal forging and multi-stephot pack rolling. A plate with dimensions about1410×677×2.7mm3was prepared.Due to formation of a fine equiaxed microstructure, the hot-workability of hot-rolled plate is increaed notably, its elogation could reach to908%when deformed at950°C、1×10-3s-1. The yield stress of the hot-rolled alloys at650°C increased from536MPa to768MPa after heat-treatment, and its elogation is13.5%.