Physical aspects of hot-working gamma-based titanium aluminides

Appel, F.; Oehring, Michael; Paul, Jonathan; Klinkenberg, Ch.; Carneiro, T.

doi:10.1016/j.intermet.2004.02.042

Cited by 89 publications

(51 citation statements)

References 28 publications

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“…In addition, heating into a multi-phase field results in sluggish grain growth, while the augmented fraction of β-phase allows for near-conventional forging [7]. This has been partly achieved by alloying γ-based TiAl alloys with β-stabilizing elements, such as Nb and Mo; however, some residual β/β 0 -phase is still present at the operating temperature [4,[8][9][10].…”

Section: Introductionmentioning

confidence: 99%

“…The α 2 -phase disorders to hcp α at the eutectoid temperature T eu and γ fully transforms into α at the γ-solvus temperature T γ,solv , also referred to as α-transus temperature T α . This high-temperature single-phase field is prone to excessive grain growth and, on deformation, inherits the anisotropic plastic behavior from the hexagonal lattice [8,23,24]. A variety of alloys based on TiAl with additions of niobium has been developed in the so-called TNB alloy series [5,[25][26][27], where Nb substitutes Ti sites and eventually stabilizes the bcc-based β-phases.…”

Section: Introductionmentioning

confidence: 99%

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Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Liss

Funakoshi

Dippenaar

et al. 2016

Metals

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Titanium aluminides find application in modern light-weight, high-temperature turbines, such as aircraft engines, but suffer from poor plasticity during manufacturing and processing. Huge forging presses enable materials processing in the 10-GPa range, and hence, it is necessary to investigate the phase diagrams of candidate materials under these extreme conditions. Here, we report on an in situ synchrotron X-ray diffraction study in a large-volume press of a modern (α 2 + γ) two-phase material, Ti-45Al-7.5Nb-0.25C, under pressures up to 9.6 GPa and temperatures up to 1686 K. At room temperature, the volume response to pressure is accommodated by the transformation γ → α 2 , rather than volumetric strain, expressed by the apparently high bulk moduli of both constituent phases. Crystallographic aspects, specifically lattice strain and atomic order, are discussed in detail. It is interesting to note that this transformation takes place despite an increase in atomic volume, which is due to the high ordering energy of γ. Upon heating under high pressure, both the eutectoid and γ-solvus transition temperatures are elevated, and a third, cubic β-phase is stabilized above 1350 K. Earlier research has shown that this β-phase is very ductile during plastic deformation, essential in near-conventional forging processes. Here, we were able to identify an ideal processing window for near-conventional forging, while the presence of the detrimental β-phase is not present under operating conditions. Novel processing routes can be defined from these findings.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Liss

Funakoshi

Dippenaar

et al. 2016

Metals

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“…Small amounts of different alloying elements (Cr, Nb, Mn, V, Si, B, C) improve the room temperature ductility, formability, tensile strength, creep and oxidation resistance [1]. Most of the previous works on hotworking of TiAl-based alloys have focused on the processing related aspects, however, only a few studies are available on details of the recovery and dynamic recrystallization (DRX) processes [2][3][4][5][6][7][8]. Therefore, it is the aim of the present work to investigate the microstructure evolution and creep behaviour during large strain torsion of Ti-45Al-4(Cr, Nb, Ta, B).…”

Section: Introductionmentioning

confidence: 99%

High strain torsion of a TiAl-based alloy

Cao

Klöden

Rybacki

et al. 2008

Materials Science and Engineering: A

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A two-phase lamellar and globular TiAl-based alloy Nb, Ta, B)) with different textures has been deformed in torsion in a Paterson-type rock deformation machine at a temperature of 1173 K under 400 MPa argon confining pressure. The shear stress -shear strain curves with increasing shear strain show a decrease or increase of shear stress in the lamellar and globular case, respectively, to a common steady state value. Activation analysis at high strains yields stress exponents of about 1.8 and an activation energy of 3.29 eV. With increasing shear strain the lamellar structure breaks down and a two-phase fine-grained globular structure develops by recrystallization with a grain size in the order of 2 microns. The weak initial fibre textures at high strains are randomized. The mechanical, microstructural and textural features indicate a transition from dislocation creep to superplastic flow.

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“…[7][8][9] Some researches have demonstrated the feasibility of the hot-working of TiAl alloys of a high Nb content. 10,11) Nevertheless, the Al content in most TiAl alloys with a high Nb content is above 45 mol%. TiAl alloys with a high Nb content and the Al range between 40 and 45 mol% have been seldom studied.…”

Section: Introductionmentioning

confidence: 99%

Creep Behavior of Ti–40Al–16Nb Intermetallic Alloy and Strengthening Effects of Minor Sc

Zhan

Koo

2006

Mater. Trans.

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The creep behavior of the Ti-40Al-16Nb alloy and the effect of the minor addition of Sc are investigated by creep tests at 1073 K under constant load from 200 to 280 MPa. The creep curve of the alloy with high Nb contents does not exhibit a steady-state region, and the minor addition of Sc added to the alloy has no effect on minimum creep rate. The creep responses of the alloys with high Nb contents are strongly correlated with tertiary creep behavior. The effects of Sc addition are apparent on the properties of tertiary creep rate and rupture life. The tertiary creep rate of the Sc containing alloy is reduced and the creep fracture life is increased. Subgrain structures of dislocations are absent in the alloys with high Nb contents during secondary creep, and the deformation of creep converges mainly at the B2 phase. A stress exponent of 4.5 estimated indicates that the mechanism of controlling creep behavior is dislocation climb. The creep fracture of the alloys is dominated by cleavage fracture over the entire fracture surface. Sc 2 O 3 particles are an effective obstacle to the propagation of cracks and the motion of dislocations.

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Physical aspects of hot-working gamma-based titanium aluminides

Cited by 89 publications

References 28 publications

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

High strain torsion of a TiAl-based alloy

Creep Behavior of Ti–40Al–16Nb Intermetallic Alloy and Strengthening Effects of Minor Sc

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Physical aspects of hot-working gamma-based titanium aluminides

Cited by 89 publications

References 28 publications

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

Hydrostatic Compression Behavior and High-Pressure Stabilized β-Phase in γ-Based Titanium Aluminide Intermetallics

High strain torsion of a TiAl-based alloy

Creep Behavior of Ti&ndash;40Al&ndash;16Nb Intermetallic Alloy and Strengthening Effects of Minor Sc

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Creep Behavior of Ti–40Al–16Nb Intermetallic Alloy and Strengthening Effects of Minor Sc