Relationship between tensile and primary creep properties of near γ-TiAl intermetallics

Beddoes, J.; Seo, Dongyi; Chen, W.R.; Zhao, L.

doi:10.1016/s0966-9795(01)00090-5

Cited by 36 publications

(21 citation statements)

References 22 publications

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“…For TiAl ϩ WMoSi with a similar fully lamellar microstructure, it was suggested previously that ␤ 0 interface precipitates may suppress microdeformation of "soft" oriented grains by inhibiting dislocation motion along interfaces, decreasing the instantaneous strain in the aged conditions at a creep stress below the yield stress. [44] Therefore, the current and previously reported results suggest that for creep stresses near or above the yield point, the instantaneous creep strain depends on the interface dislocation mobility, which can be most effectively hindered by a high density of fine lamellar interface ␤ 0 precipitates and continuous ␥/␣ 2 ϩ ␤ 0 /␥ lamellae. These same microstructural features increase the yield strength; hence, there is a direct relationship between yield strength and instantaneous strain.…”

Section: A Effect Of Lamellar Morphology On Tensile Properties and Imentioning

confidence: 64%

“…In contrast, previous studies indicated that the increase in tensile strength caused by decreasing the lamellar interface spacing did not appear to lower the instantaneous strain during creep loading at 276 MPa. [43,44] At the 140 MPa creep stress, the instantaneous strain of the 5-hour-aged condition is lower than that of the unaged condition and the 24-hour-aged conditions (Figure 7(b)). As a result of the shorter aging time, the interface ␤ 0 precipitates are smaller, but more closely spaced, than after longer aging times (Figures 14(a) through (c)).…”

Section: A Effect Of Lamellar Morphology On Tensile Properties and Imentioning

confidence: 92%

“…These results are consistent with previously reported results for fully lamellar Ti-47Al-2Nb-1Mn-0.5W-0.5Mo-0.2Si before and after aging. [44,45] D. The 96-hour-aged condition (Figure 9(a)) exhibits some cross twining in ␥ lamellae, dislocation movement blocked by the twin interfaces, and dislocations emanating from these twin interfaces. As presented in Figure 9(b), dislocations emanate from lamellar interfaces free of ␤ 0 precipitation and glide easily in ␥ lamellae-similar to the unaged condition of Figure 8(a)-but dislocation emission from interfaces with ␤ 0 precipitates is limited (Figure 9(c)).…”

Section: Creep Propertiesmentioning

confidence: 99%

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Primary creep behavior of Ti-48Al-2W as a function of stress and lamellar morphology

Seo

Zhao

Beddoes

2003

Metall Mater Trans A

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The fully lamellar microstructure of powder metallurgy Ti-48Al-2W after cooling from the ␣ region to 1280°C, followed by air cooling and aging at 950°C for up to 96 hours, is presented. Aging times as short as 5 hours result in acicular-shaped precipitates of W-rich ␤ 0 along lamellar interfaces, with the ␤ 0 size increasing with aging time. The ␤ 0 precipitates nucleate and grow in the ␣ 2 lamellae. Concurrently, with the formation of ␤ 0 , the ␣ 2 decomposes into discontinuous lamellae. Aging to precipitate ␤ 0 along lamellar interfaces increases the 760°C tensile strength (with a slight reduction of ductility) and reduces the instantaneous creep strain, since ␤ 0 precipitates at lamellar interfaces hinder interface dislocation mobility. The deformed microstructures from interrupted creep tests at 140 to 276 MPa at 760°C indicate that the precipitation of ␤ 0 along interfaces substantially reduces the primary creep strain, primarily due to the influence of ␤ 0 on interface dislocation emission and motion. These results are discussed in terms of the influence of lamellar morphology on the instantaneous creep strain and primary creep transient, and the possible creep mechanisms are highlighted.

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Section: A Effect Of Lamellar Morphology On Tensile Properties and Imentioning

confidence: 64%

Section: A Effect Of Lamellar Morphology On Tensile Properties and Imentioning

confidence: 92%

Section: Creep Propertiesmentioning

confidence: 99%

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Primary creep behavior of Ti-48Al-2W as a function of stress and lamellar morphology

Seo

Zhao

Beddoes

2003

Metall Mater Trans A

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“…Although these elements heavily segregate within cast material and lead to an increased overall density, the potential advantages of such additions on properties, particularly at high temperatures, has led to their increased use. On the contrary, other work has shown that β /B2 precipitation may increase high -temperature strength and creep resistance [10] . More importantly increased high -temperature strength and creep resistance has also been reported for such additions.…”

Section: Nb W Mo and Tamentioning

confidence: 90%

Alloy Design

2011

Gamma Titanium Aluminide Alloys

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In the TiAl literature, alloy and suitable processing technology development has played a signifi cant role for at least the last 20 years. Advances have been made, so that the strength levels achieved in technical alloys over the last few years are around double those of 20 years ago, while maintaining the same levels of roomtemperature ductility. Improvement of other properties such as creep and oxidation resistance has been achieved through alloying and the use of halogens, although improvement of other properties, such as toughness, through composition rather than microstructure has met with less success. It now seems well acknowledged that there is no universal alloy composition that is suitable for all applications; rather alloy composition must be tailored together with processing to achieve the required properties for specifi c components.Accurate information concerning the phase relationships in both binary Ti -Al and in multicomponent systems is very important in designing alloys and suitable heat treatments. This is because for a given alloy, properties are very dependent on microstructure, and microstructure is highly sensitive to composition. The high microstructure/composition sensitivity is perhaps one of the most challenging aspects in producing components from industrially produced ingot stock; as compositional variation within ingots can lead to fi nished components with a range of microstructures and thus properties. This is obviously unacceptable, especially for safety -relevant aerospace parts. A good overview concerning the infl uence of different alloying elements was published in 1993 [1] . This chapter will briefl y outline how alloys have developed over the last 20 years and discuss the different alloydesign philosophies. Effect of Aluminum ContentIn binary alloys, the aluminum level determines the initial phase to precipitate and the subsequent phase transformations that occur on solidifi cation. According to Huang and Hall [2] who published work in 1991 on binary alloys within the range Ti -(46 -60)Al made via rapid -solidifi cation processing, ductility is highest for duplex microstructures where the heat treatment is roughly in the middle of the 13 Gamma Titanium Aluminide Alloys: Science and Technology, First Edition.

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“…single phase, aCg mixture and a 2 Cg mixture. But the solidification segregation of Nb and W results in existence of the b(B 2 ) phase in the as-forged pancake, even though the HIP and forging are carried out [8]. After HT1 the b(B 2 ) phase disappears.…”

Section: Discussionmentioning

confidence: 99%

Pilot processing and microstructure control of high Nb containing TiAl alloy

Lin

et al. 2005

Intermetallics

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Relationship between tensile and primary creep properties of near γ-TiAl intermetallics

Cited by 36 publications

References 22 publications

Primary creep behavior of Ti-48Al-2W as a function of stress and lamellar morphology

Primary creep behavior of Ti-48Al-2W as a function of stress and lamellar morphology

Alloy Design

Pilot processing and microstructure control of high Nb containing TiAl alloy

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