Effects of niobium and ultrasonic action coupling on microstructure evolution and mechanical properties of Ti46Al 2.6 C alloy

Abstract

To refine microstructure, adjust the ratio of γ/α2 and improve the mechanical properties, Ti46Al 2.6 C-xNb (at. %) alloys were prepared by arc melting under the action of ultrasound. The phase composition, lamellar colony size, elements distribution, the kinds and distribution of carbides and compressive properties were investigated. Results show that as the Nb content increases, the relative content of α2 phase and Ti2AlC phase increases, and the relative content of γ phase decreases. TiC phase completely reacts to form Ti2AlC phase and its shape changes from coarse long rod to short rod. The microstructure was refined with the addition of Nb under ultrasound treatment. Lamellar colony size decreases from 36.9 to 21.5 µm, lamellar spacing decreases from 1.6 to 0.8 µm, and the length-diameter ratio of Ti2AlC decreases from 5.4 to 4.0 when the Nb content increases from 0 to 8.0 at. %. During solidification process, not only the component supercooling and heterogeneous nucleation of Nb are increased, but also the crystal grains are broken and the nucleation barrier is reduced under the action of ultrasound to promote the nucleation. The microstructure is refined and the uniformity of the element distribution is improved. Compressive results show that the strength increases from 2074.1 to 2474.2 MPa and the strain increases from 23.4% to 28.0% when the Nb content increases from 0 to 4 at. %. The refinement of lamellar colony and Ti2AlC, the ratio of γ/α2 and solid-solution of Nb are the main reasons for improving compressive properties.