Precipitation behavior of ωo phase and texture evolution of a forged Ti-45Al-8.5Nb-(W, B, Y) alloy during creep
- State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China)
- State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an, Shaanxi 710072 (China)
- Institute for Advanced Materials and Technology, University of Science and Technology Beijing, Beijing 100083 (China)
Highlights: • The morphology of ω{sub o} and residual β{sub o} phases depends on creep temperature and stress. • Stress can increase the tendency of the α{sub 2} to ω{sub o} phase transformation. • The strength of the texture components depend on temperature and stress. • β{sub o}(ω{sub o}) precipitation retards the growth of recrystallized γ grains. • ω{sub o} precipitation resists and deflects the crack during the crack propagation. - Abstract: Creep rupture tests of the as-forged Ti-45Al-8.5Nb-(W,B,Y) alloy with a duplex microstructure were carried out at 750–850 °C and 130–300 MPa. An investigation was performed to study the effects of temperature and stress on the microstructure and texture evolution, as well as on the creep properties of the forged high Nb-containing TiAl alloy with a duplex microstructure. The results show that the stress exponent n = 2.8–3.3, and the creep activation energy values are in the range of 300–400 kJ/mol. After creep, a regular arrangement of ω{sub o} precipitations was observed in the β{sub o} region. The un-transformed β{sub o} phase, which remained in the ω{sub o} interval, was examined using high resolution transmission electron microscope (HRTEM). It is shown that the growth of ω{sub o} precipitations and the morphology of residual β{sub o} phases are related to the creep temperature and stress. Certain β{sub o} stabilizer elements, such as Nb, segregate into α{sub 2} plates and cause ω{sub o} precipitation during dissolution of α{sub 2} plates at high temperature. The interfacial structure between the ω{sub o} and α{sub 2} phases was studied in detail using HRTEM. Meanwhile, texture evolution and dynamic recrystallization of the γ phase were studied using electron backscatter diffraction (EBSD). Observations on the deformation structure also demonstrate that ω{sub o} precipitation acts as an obstacle inhibiting crack propagation and growth of the γ phase. The corresponding formation mechanism and possible effects on creep are discussed.
- OSTI ID:
- 22804883
- Journal Information:
- Materials Characterization, Vol. 136; Other Information: Copyright (c) 2017 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 1044-5803
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ACTIVATION ENERGY
ALLOY SYSTEMS
ALUMINIUM COMPOUNDS
BACKSCATTERING
BORON ADDITIONS
CREEP
DEFORMATION
ELECTRON DIFFRACTION
MICROSTRUCTURE
NIOBIUM COMPOUNDS
PHASE TRANSFORMATIONS
PRECIPITATION
PRESSURE RANGE MEGA PA 100-1000
RECRYSTALLIZATION
STRESSES
TEXTURE
TITANIUM COMPOUNDS
TRANSMISSION ELECTRON MICROSCOPY
TUNGSTEN ADDITIONS
YTTRIUM ADDITIONS