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

• Successfully adjusted the solid-liquid phase region to increase the effective time of ultrasound in the primary nucleation and growth process. • TiC completely forms Ti 2 AlC phase with the increase of niobium content under the action of ultrasound. • The Ti 2 AlC and lamellar colony are refined because niobium causes component undercooling and further increases heterogeneous nucleation. • The compression performance of TiAl composites is improved, the maximum strength is 2474.2 MPa and the maximum strain is 28.0% with 4 at% Nb. To refine microstructure, adjust the ratio of γ/α 2 and improve the mechanical properties, Ti46Al 2.6 C- x Nb (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 α 2 phase and Ti 2 AlC phase increases, and the relative content of γ phase decreases. TiC phase completely reacts to form Ti 2 AlC 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 Ti 2 AlC 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 Ti 2 AlC, the ratio of γ/α 2 and solid-solution of Nb are the main reasons for improving compressive properties. [ABSTRACT FROM AUTHOR]