Thermal Stability of Microstructures in Low-Density Ti2AlNb-Based Alloy Hot Rolled Plate
Multielement and multiphase intermetallic alloys based on an ordered orthorhombic(O)phase Ti2AlNb,where the presence of a long-range order superlattice structure effectively impedes the movement of dislocations and high-temperature diffusion,are a class of highly promising lightweight high-temperature structural materials for aerospace applications due to their high specific strength and superi-or fracture toughness.Thermal stability of microstructures in the hot rolled sheet of a low-density Ti2AlNb-based alloy has been investigated in a temperature range from 600℃ to 1100℃ for 12 h via OM,SEM,XRD,and TEM/STEM.The results showed that the initial Ti2AlNb-based alloy hot rolled sheet consisted of α2,B2,and O phases.Furthermore,the Ti2AlNb-based alloy hot rolled sheet at 600℃ for 12 h consist-ed of α2,B2,and O phases,where the particle shaped α2 phase was distributed in the B2 matrix,and lath-like O phase lay inbetween the α2 particles.The spheroidization of the α2 phase started to occur along with the coarsening and solutionizing of the lath O phase in the B2 matrix at a temperature between 800℃ and 900℃ for 12 h,while the hot rolled Ti2AlNb-based alloy plate was still composed of α2,B2,and O phases.When the temperature reached 950℃,the O phase disappeared in the B2 matrix.Only α2+B2 two phases were present in the hot rolled Ti2AlNb-based alloy at 950-1000℃ for 12 h,where the α2 phase was spheroidized and tended to distribute surrounding B2 grain boundaries.When the tempera-ture rose to 1100℃,the alloy contained a B2 single phase with only some residual α2 phase.Moreover,the Vickers microhardness contour vs temperature plot revealed that a peak hardness of as high as 509 HV appeared at 600℃ due to the presence of numerous fine O laths.
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