Coherency stresses and interface-related deformation phenomena in two-phase titanium aluminides

Appel, F.; Christoph, U.

doi:10.1016/s0966-9795(99)00030-8

Cited by 56 publications

(29 citation statements)

References 19 publications

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“…The process was found to be closely related to mismatch structures and coherency stresses present at the semicoherent interfaces. [3,8,18,23,24] The coherency stresses are comparable with the yield stress of the material and give rise to the formation of loop structures adjacent to the interfaces (Fig. 1c).…”

Section: Generation Of Perfect Dislocationsmentioning

confidence: 93%

Recent Progress in the Development of Gamma Titanium Aluminide Alloys

Appel¹,

Brossmann²,

Christoph³

et al. 2000

Adv. Eng. Mater.

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369

103

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Intermetallic titanium aluminides offer an attractive combination of low density and good oxidation and ignition resistance with unique mechanical properties. These involve high strength and elastic stiffness with excellent high temperature retention. Thus, they are one of the few classes of emerging materials that have the potential to be used in demanding high‐temperature structural applications whenever specific strength and stiffness are of major concern. However, in order to effectively replace the heavier nickel‐base superalloys currently in use, titanium aluminides must combine a wide range of mechanical property capabilities. Advanced alloy designs are tailored for strength, toughness, creep resistance, and environmental stability. These concerns are addressed in the present paper through global commentary on the physical metallurgy and associated processing technologies of γ‐TiAl‐base alloys. Particular emphasis is paid on recent developments of TiAl alloys with enhanced high‐temperature capability.

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Section: Generation Of Perfect Dislocationsmentioning

confidence: 93%

Recent Progress in the Development of Gamma Titanium Aluminide Alloys

Appel¹,

Brossmann²,

Christoph³

et al. 2000

Adv. Eng. Mater.

Self Cite

369

103

View full text Add to dashboard Cite

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“…Accommodation of lattice misfit between adjacent lamellae leads to dense arrangements of interfacial dislocations with different Burgers vectors and high residual coherency stresses. [16,30] Transmission electron microscopy (TEM) analysis has shown that the coherency stresses are comparable with the yield stress of the material and give rise to a long-range internal stress field varying in amplitude and direction. Under ͭ111ͮ ␥ ' (0001) ␣ 2 and ͗11 0] ␥ ' ͗112 0͘ ␣ 2 creep conditions, relaxation of these stresses occurs due to the emission of interfacial dislocations, which probably give rise to the high primary creep rate of the otherwise creepresistant lamellar alloys.…”

Section: A Interface Related Creep Mechanismsmentioning

confidence: 99%

Creep behavior of TiAl alloys with enhanced high-temperature capability

Appel

Paul

Oehring

et al. 2003

Metall Mater Trans A

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For high-temperature applications, creep strength is of major concern, in addition to oxidation and corrosion resistance, and determines the application range of titanium aluminide alloys in competition with other structural materials. Thus, this work was aimed at identifying mechanisms of creep deformation and microstructural degradation and at developing alloying concepts with respect to an enhanced high-temperature capability. The analysis shows that dislocation climb controls deformation in the range of the intended operation temperatures. Further, complex processes of phase transformations, recrystallization, and microstructural coarsening were observed, which contribute to microstructural degradation and limit component life in long-term service. By alloying with high contents of Nb, both room-and high-temperature strength properties can be improved as Nb increases the activation energy of diffusion and increases the propensity for twinning at ambient temperature. For alloys with enhanced hightemperature capability, microalloying with carbon is also of particular use, because carbide precipitates effectively hinder dislocation motion and are thought to increase microstructural stability.

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“…Accommodation of the misfit, which occurs because of differences in lattice parameters and crystal structure, leads to dense structures of interfacial dislocations and coherency stresses. [13,14] These structural features result in a significant Fig. 2-Eutectoid temperatures T eut and a-transus temperatures T a of alloy 1 (Ti-46.5Al) and alloy 2 (Ti-46.5Al-5Nb).…”

Section: Methodsmentioning

confidence: 99%

Hot-Workability of Gamma-Based TiAl Alloys during Severe Torsional Deformation

Fröbel¹,

Appel²

2007

Metall Mater Trans A

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Wrought TiAl products manufactured by conventional hot-working procedures, such as forging and extrusion, suffer from structural and chemical inhomogeneities, which are major concerns for the reliability of components. In an attempt to overcome these problems, TiAl alloys were hot worked by torsional deformation. Using this method, a much higher strain and mechanical work can be imparted, which triggers dynamic recrystallization. The metallurgical potential of this technique will be assessed. Particular emphasis is placed on shear localization processes, which often lead to premature failure of the workpiece.

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Coherency stresses and interface-related deformation phenomena in two-phase titanium aluminides

Cited by 56 publications

References 19 publications

Recent Progress in the Development of Gamma Titanium Aluminide Alloys

Recent Progress in the Development of Gamma Titanium Aluminide Alloys

Creep behavior of TiAl alloys with enhanced high-temperature capability

Hot-Workability of Gamma-Based TiAl Alloys during Severe Torsional Deformation

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