Fig. 1 Schematic diagram of DB and heat treatment including solution and aging treatments in the present work, fast heating (FH) represents that the furnace temperature firstly reaches up to specifical temperature, followed by heating the specimens

Fig. 2 Tensile specimens: a schematic illustration of directionality of sample on as-received sheet and bonded sheets for tensile tests, geometries of tensile test specimen at 650 °C b and room temperature c, unit: mm

Fig. 3 SEM and TEM microstructures of as-received Ti2AlNb alloy, a secondary electron image with a magnified zone, b, b1 bright field (BF) image showing detailed grains, c the selected area electron diffraction (SAED) patterns of the positions at b1 marked by yellow circles and numbers

Fig. 4 SEM micrographs of the DB sample: a the bonded interface, b Ti2AlNb substrate, a1, b1 the corresponding amplified images

Fig. 5 Secondary electron images of samples at the substrates after solution and aging treatments: a the DB-1000/750 sample, b the DB-1000/800 sample, a1, b1 the corresponding magnified zones

Fig. 6 TEM a, b, c, STEM d, and EDS e characterizations showing the microstructures and element distribution in the DB-1000/750 sample: a, b BF images, c SAED patterns at the positions in a, b marked by yellow circles and numbers, d high-angle annular dark-field (HAADF) image, e HAADF image and element (Ti, Al, Nb) distribution

Fig. 7 EBSD characterization of the as-received sample a, f, substrate of the DB sample b, e, and the DB-1000/750 sample c: a, b, c phase map (red, blue, and green: O, B2, and α2 phases, respectively), d area fraction of the three phases, e inverse pole figure (IPF) map upon Y parallel to the normal direction (ND), f pole figure (PF) map showing the crystallographic parallel relationship between O and α2 grains in a, and the relationship between B2 and α2 grains in a

Fig. 8 Mechanical properties of Ti2AlNb alloy at room temperature and 650 °C: a engineering stress-strain curves at room temperature, b engineering stress-strain curves at 650 °C

Fig. 9 TEM observation of the as-received sample after tensile fracture at room temperature: a, b dislocation pile-up and tangle at fine O, α2, and B2 matrix, c distribution and characteristic of dislocations, c1 high density of dislocations within B2 grains. The scanning area is approximately 4 mm away from the fracture surface

Fig. 10 TEM characterization of the DB-1000/750 sample after tensile fracture at room temperature: a, b planar slip of dislocations at fine O, α2, and B2 matrix, c high density of dislocations within B2 grains, d a SAED pattern in c1. The scanning area is approximately 4 mm away from the fracture surface

Fig. 11 EBSD characterization of the as-received sample a, d, the substrate of the DB sample b, e, and the DB-1000/750 sample c, f after tensile fracture: a-c the whole kernel average misorientation (KAM) maps, d-f the local KAM value crossing the B2, O, and α2 grains. White arrows in a-c represent the distance in d-f

Fig. 12 SEM observation on the fracture surfaces of Ti2AlNb alloy after tension at room temperature: a the DB sample, b the DB-1000/800 sample, and the corresponding magnified zones

Fig. 13 Secondary electron images showing fracture section of Ti2AlNb alloy after tension at room temperature: a, b, c micro-cracks near fracture in the DB sample, d, e fracture crack path in the substate of DB-1000/800 sample, e1 the corresponding magnified zone