Thermal stability of a fully lamellar Ti-48Al-2Cr-2Nb-1B alloy

Hu, Dawei; Godfrey, A.; Loretto, M. H.

doi:10.1016/s0966-9795(98)80019-8

Cited by 56 publications

(25 citation statements)

References 4 publications

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“…[10] Consequently, many recent studies have been concentrated on the thermal stability of the lamellar structure. [10][11][12][13][14][15][16] It was concluded that lamellar instability was mainly due to decomposition of the ␣ 2 phase because the volume fraction and the composition of constituent phases did not reach equilibrium. [10,14] It was also reported that the decomposition of ␣ 2 phase at elevated temperatures occurred in different phase transformation modes: intrapacket termination migration coarsening, [11] diffusion coarsening, [17] and discontinuous coarsening.…”

Section: Introductionmentioning

confidence: 99%

“…[10][11][12][13][14][15][16] It was concluded that lamellar instability was mainly due to decomposition of the ␣ 2 phase because the volume fraction and the composition of constituent phases did not reach equilibrium. [10,14] It was also reported that the decomposition of ␣ 2 phase at elevated temperatures occurred in different phase transformation modes: intrapacket termination migration coarsening, [11] diffusion coarsening, [17] and discontinuous coarsening. [11,[18][19][20][21] In a detailed study on the decomposition of ␣ 2 phase, [16] three Ti-47Al alloys were annealed at 1400°C for 1 hour, followed by furnace cooling, and aged at 800°C, 1000 °C, and 1200 °C.…”

Section: Introductionmentioning

confidence: 99%

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Microstructural stability of fine-grained fully lamellar XD TiAl alloys by step aging

Zhu

Maruyama

Seo

et al. 2005

Metall Mater Trans A

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XD TiAl alloys (Ti-45 and 47Al-2Nb-2Mn ϩ 0.8 vol pct TiB 2 ) (at. pct) were oil quenched to produce fine-grained fully lamellar (FGFL) structures, and aging treatments at different temperatures for different durations were carried out to stabilize the FGFL structures. Microstructural examinations show that the aging treatments cause phase transformation of ␣ 2 to ␥, resulting in stabilization of the lamellar structure, as indicated by a significant decrease in ␣ 2 volume fraction. However, several degradation processes are also introduced. After aging, within lamellar colonies, the ␣ 2 lamellae become finer due to dissolution, whereas most of the ␥ lamellae coarsen. The dissolution of ␣ 2 involves longitudinal dissolution and lateral dissolution. In addition, at lamellar colony boundaries, lamellar termination migration, nucleation and growth of ␥ grains, and discontinuous coarsening occur. With the exception of longitudinal dissolution, all the other transformation modes are considered as degradation processes as they result in a reduction in ␣ 2 /␥ interfaces. Different phase transformation modes are present to varying degrees in the aged FGFL structures, depending on aging conditions and Al content. A multiple step aging reduces the drive force for phase transformation at high temperature by promoting phase transformation via longitudinal dissolution at low temperatures. As a result, this aging procedure effectively stabilizes the lamellar structure and suppresses other degradation processes. Therefore, the multiple step aging is suggested to be an optimal aging condition for stabilizing FGFL XD TiAl alloys.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Microstructural stability of fine-grained fully lamellar XD TiAl alloys by step aging

Zhu

Maruyama

Seo

et al. 2005

Metall Mater Trans A

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“…[12][13][14][15][16][17][18] It has been found that the thermal instability is mainly decomposition of 2 phase because the volume fraction as well as the composition of constituting phases does not reach equilibrium prior to creep test. 12,14) Thus, stabilization treatment prior to creep test has been carried out to improve the microstructural stability. 12) Another important microstructure factor to influence the creep resistance is the morphology of the grain (or colony) boundary.…”

Section: Introductionmentioning

confidence: 99%

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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“…• C for 3000 h resulted in the almost complete removal of α 2 [31]. No decomposition of the α 2 lamellae into α 2 +β and no recrystallization of β-phase were observed.…”

Section: Characterization Of Microstructure and Mechanical Propertiesmentioning

confidence: 96%

Thermal stability and precipitation strengthening of fully lamellar Ti-45Al-5Nb-0.2B-0.75C alloy

Čegan¹,

Szurman²

2018

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The alloy with a composition Ti-45Al-5Nb-0.2B-0.75C (at.%) was prepared by induction melting and centrifugal casting. The fully lamellar microstructure of the alloy without carbides was produced by heat treatment consisting of hot isostatic pressing (HIP) and solution annealing followed by cooling to room temperature. The stability of the fully lamellar γ(TiAl) + α2(Ti3Al) microstructure was studied at temperatures of 750, 850 and 950• C up to an ageing time of 3400 h. The microstructure analysis shows that the most dominant change in the microstructure was the α2 lamellae thinning, which was more pronounced at a higher ageing temperature and longer time. The formation of recrystallized γ grains and Ti2AlC carbides was observed during ageing at the temperatures of 850 and 950• C. The microstructural changes affected the microhardness at room temperature (RT) and compression yield strength at temperatures ranging from RT to 950K e y w o r d s : titanium aluminides, thermal stability, microstructure, carbides, yield strength

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Thermal stability of a fully lamellar Ti-48Al-2Cr-2Nb-1B alloy

Cited by 56 publications

References 4 publications

Microstructural stability of fine-grained fully lamellar XD TiAl alloys by step aging

Microstructural stability of fine-grained fully lamellar XD TiAl alloys by step aging

Grain Boundary Morphology and Its Effect on Creep of TiAl Alloys

Thermal stability and precipitation strengthening of fully lamellar Ti-45Al-5Nb-0.2B-0.75C alloy

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