Crystallographic orientation relationships and interfacial structures between reinforcement and matrix phases in an in situ (Ti, Nb)B/Ti2AlNb composite

Abstract High-performance (Ti, Nb)B/Ti2AlNb composites are promising high-temperature structural materials for the new generation of aerospace engines. The interfaces between the (Ti, Nb)B reinforcement and matrix phases (i.e. O-Ti2AlNb, α2-Ti3Al and B2 phases) affect the mechanical properties of the composites largely. In this study, the properties of the interfaces were systematically revealed after fabricating a (Ti, Nb)B/Ti2AlNb composite by low-energy ball-milling and spark plasma sintering (SPS). A high-resolution transmission electron microscopy (HRTEM) was adopted to evaluate the crystallographic orientation relationships (ORs) and interfacial structures. (Ti, Nb)B maintains three coherent interfaces with the matrix, and the preferred ORs between them can be expressed as [11 2 ¯ 0]α2//[010](Ti, Nb)B and ( 1 ¯ 100)α2//(100)(Ti, Nb)B; [10] 1 ¯ O//[010](Ti, Nb)B and (110)O//(100)(Ti, Nb)B; [11] 1 ¯ B2//[010](Ti, Nb)B and ( 1 ¯ 12)B2//(100)(Ti, Nb)B. The results of first-principles calculations indicated that the ( 1 ¯ 100)α2/(100)(Ti, Nb)B interface possesses a higher bonding strength compared with the (110)O/(100)(Ti, Nb)B and ( 1 ¯ 12)B2/(100)(Ti, Nb)B interfaces, and the (Ti, Nb)B reinforcement and the matrix are bonded through strong ionic bonds and weak covalent bonds. Moreover, based on Bramffit’s lattice mismatch theory, it was found that the (Ti, Nb)B reinforcement acts as an effective substrate in promoting the heterogeneous nucleation and preferred precipitation of the α2 phase. Suppressing the brittle α2 precipitate around the reinforcement improves the ductility of the composite obviously.