Microstructures and fracture toughness of Ti–(43–48)Al–2Cr–2Nb prepared by electromagnetic cold crucible directional solidification

•B2 phase is mainly induced by lower Al content and β stabilizing elements, Cr and Nb.•The fracture toughness is influenced by both lamellar spacing and B2 phase.•B2 phase has different effects on KQ with respect to different lamellar orientations.

In the present paper, the microstructures of directionally solidified Ti–(43–48)Al–2Cr–2Nb alloys prepared by electromagnetic cold crucible directional solidification technique were studied in detail. The results show that with the decrease of Al content, the interlamellar spacing of α2/γ decreases, but the volume fraction of B2 phase increases. In addition, the fracture toughness of these alloys with different lamellar orientation was investigated by single edge notched beam three-point bending test (SENB). It is revealed that B2 phase has greatly impacted on the fracture toughness. When the laminates are perpendicular to the loading stress, the increasing of B2 phase leads to a lower fracture toughness value. On the contrary, B2 phase becomes barriers for crack propagations and increases fracture toughness value when the laminates are parallel to the loading stress.