Effects of Nb on Microstructure and Mechanical Properties of Ti42Al2.6C Alloys

Ti42Al2.6C–xNb (x = 0, 2, 4, 6, and 8 at%, similarly hereinafter) alloys are synthesized by melting to investigate the effects of Nb on microstructure and mechanical properties, especially the formation of B2 phase and high temperature tensile properties. The results show that lamellar colony size decreases from 33.3 to 13.2 µm and lamellar space decreases from 193.4 to 139.6 nm with increasing Nb from 0 to 8%. Lattice parameters of γ and α₂ phase change and B2 phase forms among lamellar colonies with the addition of Nb. The volume fraction of B2 phases and content of Nb in Ti₂AlC phases increase with increasing Nb. B2 phases form between lamellar colonies because of Nb segregation. As high‐melting‐point element, Nb increases heterogenous nucleation particles and impedes grain growing. Compressive strength increases from 1568 to 1912 MPa with increasing Nb from 0 to 6% and then decreases at 8% Nb. Tensile strength at 750 °C can reach 465 MPa and the strain is only 2.4% when the Nb content is 6%. The increased strength is resulted from refined microstructure and solid solution of Nb. And the decreased strength is because many B2 phases acts as crack source.