Effects of lamellar spacing, volume fraction and grain size on creep strength of fully lamellar TiAl alloys

Maruyama, Kouichi; R.Yamamoto, R.Yamamoto; Nakakuki, Hideo; Fujitsuna, Nobuyuki

doi:10.1016/s0921-5093(97)00612-6

Cited by 154 publications

(72 citation statements)

References 26 publications

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“…From previous studies, it is known that equiaxed grains at the grain boundaries and wide lamellar spacing are detrimental to the creep resistance. 4,5) Therefore, it is postulated that much better creep resistance for the stabilized FL microstructure benefits from its good grain boundary stability. The well-interlocked grain boundaries inhibit GBS effectively by lamellar incursions and reduce microstructural degradation at the grain boundaries greatly.…”

Section: Discussionmentioning

confidence: 99%

“…4) Many works have been carried out to study the effect of microstructural parameters of the fully lamellar alloys, such as lamellar spacing, volume fraction of constituent phases and lamellar grain size, on creep properties. [5][6][7][8][9][10] It has been found that the creep rate of TiAl alloys is independent of grain size when it is greater than 100 mm, and grain size can be reduced to 100 mm without loosing creep resistance. 5) Also, the creep rate of TiAl alloys is insensitive to the volume fraction of constituent phases.…”

Section: Introductionmentioning

confidence: 99%

“…[5][6][7][8][9][10] It has been found that the creep rate of TiAl alloys is independent of grain size when it is greater than 100 mm, and grain size can be reduced to 100 mm without loosing creep resistance. 5) Also, the creep rate of TiAl alloys is insensitive to the volume fraction of constituent phases. 5) However, decreasing lamellar spacing greatly improves the creep resistance, suggesting lamellar refinement as an important way to improve the creep resistance.…”

Section: Introductionmentioning

confidence: 99%

“…5) Also, the creep rate of TiAl alloys is insensitive to the volume fraction of constituent phases. 5) However, decreasing lamellar spacing greatly improves the creep resistance, suggesting lamellar refinement as an important way to improve the creep resistance. [6][7][8] The stability of lamellar structure of TiAl alloys is greatly important to improve the creep resistance, 11) and the microstructural instability can cause a reduction in strength and creep resistance by as much as 20%.…”

Section: Introductionmentioning

confidence: 99%

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Grain Boundary Morphology and Its Effect on Creep of TiAl Alloys

et al. 2004

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Three kinds of microstructures with different grain boundary morphologies and their creep properties of a Ti-47Al-2Nb-2Mn+0.8 vol%TiB 2 alloy are investigated. Tensile creep tests and microstructural examinations indicate that a stabilized fine-grained fully lamellar (FGFL) microstructure with relatively smooth grain boundaries shows inferior creep resistance. A stabilized fully lamellar (FL) microstructure with well-interlocked grain boundaries and wider lamellar spacing yields reduced minimum strain rate and extended creep rupture life. Furthermore, a nearly lamellar microstructure (NL) with well-interlocked grain boundaries exhibits better creep resistance than the stabilized FGFL microstructure though it has four times wider lamellar spacing and 15 vol% equiaxed grains at the grain boundaries, but worse creep resistance than the stabilized FL microstructure. Examinations to the deformed microstructures show that grain boundary instability involving spheroidization of the lamellae is a major microstructural degradation process, resulting in fine globular regions at the grain boundaries. Voids develop along the grain boundaries, particularly in the fine globular regions, leading to intergranual fracture. It is suggested that grain boundary sliding (GBS) is operating in the stabilized FGFL microstructure, and promotes mutually with the grain boundary instability during subsequent creep deformation, resulting in increased minimum strain rate and shortened tertiary stage. The well-interlocked grain boundary inhibits the onset of GBS and enhances the grain boundary stability effectively. These results demonstrated that the grain boundary stability has a great effect on creep behavior of TiAl Alloys.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Grain Boundary Morphology and Its Effect on Creep of TiAl Alloys

et al. 2004

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“…[6][7][8][9][10][11][12][13][14][15][16][17] Systematically increasing the volume fraction of the lamellar constituent in a microstructure composed of equiaxed c grains and colonies of c + a 2 lamellar leads to lower creep rates and extended creep lives. [8] In addition, significantly reduced creep rates have been observed with finer lamellar spacings in FL polycrystalline microstructures containing 140 < k < 660 nm for Ti-47Al, [7] 120 < k < 450 nm for Ti-48Al, [8] 55 < k < 400 nm for Ti-45-2Nb-2Mn + 0.8 vol pct TiB 2, [15] where the characteristic lamellar spacing (k) represents the average spacing of both the a 2 and c lamellae.…”

Section: Introductionmentioning

confidence: 99%

In Situ Observations of the Deformation Behavior and Fracture Mechanisms of Ti-45Al-2Nb-2Mn + 0.8 vol pct TiB2

Muñoz‐Moreno

Boehlert

Pérez‐Prado

et al. 2011

Metall Mater Trans A

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The deformation and fracture mechanisms of a nearly lamellar Ti-45Al-2Nb-2Mn (at. pct) + 0.8 vol pct TiB 2 intermetallic, processed into an actual low-pressure turbine blade, were examined by means of in situ tensile and tensile-creep experiments performed inside a scanning electron microscope (SEM). Low elongation-to-failure and brittle fracture were observed at room temperature, while the larger elongations-to-failure at high temperature facilitated the observation of the onset and propagation of damage. It was found that the dominant damage mechanisms at high temperature depended on the applied stress level. Interlamellar cracking was observed only above 390 MPa, which suggests that there is a threshold below which this mechanism is inhibited. Failure during creep tests at 250 MPa was controlled by intercolony cracking. The in situ observations demonstrated that the colony boundaries are damage nucleation and propagation sites during tensile creep, and they seem to be the weakest link in the microstructure for the tertiary creep stage. Therefore, it is proposed that interlamellar areas are critical zones for fracture at higher stresses, whereas lower stress, high-temperature creep conditions lead to intercolony cracking and fracture.

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Effects of Microstructure, Alloying and C and Si Additions on Creep of Gamma TiAl Alloys

Kim¹,

Kim

2014

Gamma Titanium Aluminide Alloys 2014

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Effects of lamellar spacing, volume fraction and grain size on creep strength of fully lamellar TiAl alloys

Cited by 154 publications

References 26 publications

Grain Boundary Morphology and Its Effect on Creep of TiAl Alloys

Grain Boundary Morphology and Its Effect on Creep of TiAl Alloys

In Situ Observations of the Deformation Behavior and Fracture Mechanisms of Ti-45Al-2Nb-2Mn + 0.8 vol pct TiB2

Effects of Microstructure, Alloying and C and Si Additions on Creep of Gamma TiAl Alloys

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