High-temperature tensile behaviors and microstructural evolutions of a directionally solidified Ti–45Al–5Nb–2Mn alloy

Investigations on the high-temperature tensile performances and deformation behaviors of the directionally solidified Ti–45Al–5Nb–2Mn alloy revealed that an increase in the tensile temperature resulted in the occurrence of brittle-ductile transition (BDT) and the BDT temperature was beyond 1173 K. The mixed mode of inter- and trans-lamellar fracture governed the brittle fracture, and except for dimples, there were split lamellae on the ductile fracture surface. The main cracks propagated along a tortuous path and multiple secondary cracks were formed adjacent to the main cracks. The dislocation mechanism controlled the high-temperature tensile deformation. The lamellar interface remained flat at 1073 K and 1173 K, but there was significant strain existing at the lamellar interface, which made the orientation relation of α₂ lath and γ lath change to be ${\left(200\right)}_{\gamma }//{\left(01\bar{1}0\right)}_{\alpha 2}$and ${\left[001\right]}_{\gamma }//{\left[0001\right]}_{\alpha 2}$. At the tensile deformation of 1273 K, the lamellae coarsened irregularly by the phase degradation reaction of α₂→γ and dynamic recrystallization.