Environmental effect on mechanical properties of TiAl base alloys

Nakamura, Morihiko; Hashimoto, Keizo; Tsujimoto, Tokuzou

doi:10.1557/jmr.1993.0068

Cited by 44 publications

(19 citation statements)

References 19 publications

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“…Nevertheless, it is hard to say whether or not the environmental embrittlement occurs in those three microstructures, because the ductilities of those in a vacuum are too poor to differentiate further loss of ductility. This is consistent with Nakamura's study [8] that the environmental effect on ductility is scarcely observed in the alloys having low ductility below 1% in a vacuum.…”

Section: Discussionsupporting

confidence: 93%

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Effect of microstructure on environmental embrittlement in a TiAl base alloy

Kim

Lee

1998

Metals and Materials

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The effect of different microstructure on environmental embrittlement in a chromium-containing TiA1 alloy has been analyzed. The alloys having fully lamellar, nearly lamellar and duplex structure exhibited no apparent difference in the fracture strength and the tensile elongation at two test environments, vacuum and air. The near gamma alloy shows more strength higher and ductility in the vacuum than in the air. Tensile ductility increased to 3.5% in the vacuum, compared with 0.3% in the air. It can be argued that the gamma phase itself has relatively high intrinsic ductility, although a relationship with the ductility of alpha-2 is not yet clarified. An important factor to determine the environmental effect is the morphology and the volume fraction of alpha-2 phase in the alloy.

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Section: Discussionsupporting

confidence: 93%

“…Furthermore, Nakamura and his colleagues [8,11] have reported that environmental embfittlement even can be affected by the alloy chemistry. However, the effect of the microstructure on environmental embrittlement is not yet understood.…”

Section: Introductionmentioning

confidence: 99%

Effect of microstructure on environmental embrittlement in a TiAl base alloy

Kim

Lee

1998

Metals and Materials

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“…The environmental embrittlement of these intermetallic compounds is caused by hydrogen which is produced through reaction of the material surface with moisture in air 9) or hydrogen gas. TiAl based alloys also exhibit environmental embrittlement in laboratory air and hydrogen gas at room temperature, 10,11) and the microstructure of the alloys affects the environmental embrittlement at room temperature. 12) Furthermore TiAl based alloys exhibit the reduction of elongation in a hydrogen gas not only at room temperature but also at 573 K. 13) The environmental embrittlement of intermetallic compounds have hardly been investigated at elevated temperatures, although L1 2 type intermetallic alloys such as Ni 3 Si and Ni 3 Al based alloys are reported to exhibit smaller elongation in air than in vacuum at elevated temperatures.…”

Section: Introductionmentioning

confidence: 99%

“…At 973 K, just a few amounts of cleavage facets mixed with grain boundary facets are observed for the specimens tested both in hydrogen gas and in vacuum. These observations probably indicate that the hydrogen embrittlement of the TiAl alloy is caused by lowering of the cleavage fracture strength rather than the grain boundary strength even at higher temperature as well as at room temperature, 10) although the grain boundary strength may also decrease with increasing temperature.…”

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confidence: 97%

Tensile Properties of TiAl Based Alloy in a Gaseous Hydrogen Atmosphere in a Temperature Range from Room Temperature to 973 K

et al. 2003

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Ti-48Al-2Cr-2Nb (at%) with a g phase structure was tensile-tested in a high purity hydrogen gas in a temperature range of room temperature to 973 K. The reduction of elongation was observed in hydrogen gas in the entire temperature range, although the fracture surface changed mainly from cleavage to grain boundary facets both in vacuum and in hydrogen gas as the temperature increases. From transmission electron microscopy, fractography, the content of hydrogen introduced during tensile testing, and consideration of the diffusion rate of hydrogen, the hydrogen environmental embrittlement of the TiAl based alloy is suggested to result not from the formation of hydrides but from local accumulation of solute hydrogen introduced by dislocations from the test environment during testing. The hydrogen introduced during tensile deformation mainly decreases not grain boundary strength but cleavage strength, and then the reduction of elongation in hydrogen gas is caused by the decrease of the transgranular strength in the wide temperature range, although the grain boundary strength may also decrease with increasing temperature. KEY WORDS: TiAl based alloy; hydrogen gas; environmental embrittlement; tensile property; elevated temperature.Al: 33.52 (48.2 at%), Nb: 4.71 (1.97 at%), Cr: 2.71 (2.02 at%), Si: 0.007, Mn: Ͻ0.005, Fe: 0.10, Ni: 0.02, Cu: Ͻ0.005, C: 0.008, O: 0.063, N: 0.0041, H: 0.0009, Ti: bal. The alloy ingot of about 20 kg was prepared by inductionskull-melting in an argon atmosphere, and then the alloy bars of 16 mm in diameter were prepared by hot extrusion at 1 473 K. The extrusion ratio was 7.2.Tensile specimens with a gage length of 15 mm and a gage section of 1.5ϫ4 mm were machined using an electric discharging machine (EDM). The tensile direction of the specimens was parallel to the longitudinal direction of the extruded bar. After mechanical polishing, they were heat treated at 1 313 K for 50 h in an argon atmosphere in order to obtain a g-single phase structure. After mechanical polishing followed by electro-polishing, the specimens were tensile-tested in a temperature range of room temperature to 973 K using a screw-driven testing machine at a constant crosshead speed of 0.2 mm/min (a nominal strain rate of 2ϫ10 Ϫ4 s Ϫ1). The test environments were vacuum (Ͻ4ϫ10 Ϫ4 Pa) and a flowing high purity hydrogen gas (99.99999 %) of 1 atm. The test chamber, which was attached to the testing machine, was evacuated to better vacuum than 4ϫ10 Ϫ4 Pa, and then backfilled with the high purity hydrogen gas. This process was repeated four times, before the specimens were tested in the flowing hydrogen gas. The tensile tests were carried out after the specimens were heated to a given temperature followed by holding for 15 min in each environment. In most cases, three specimens were tested in each condition, and the average values were used for the tensile properties.The fracture surfaces and microstructures of the specimens were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM)....

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“…[8][9][10][11][12] Moisture-induced embrittlement of L1 2 -type intermetallic alloys has been considered to be caused by hydrogen released from moisture in air, 13) and to involve micro-processes such as generation of hydrogen by decomposition of moisture on the alloy surface, absorption of hydrogen into the alloy, migration and condensation of hydrogen at grain boundaries in front of a propagating micro crack introduced from alloy surface during deformation. [14][15][16] Eventually, grain boundary cohesion and associated plastic work are reduced by stress field arising in front of a propagating micro crack due to hydrogen condensation, and consequently intergranular fracture occurs, resulting in low ductility.…”

Section: Introductionmentioning

confidence: 99%

Effect of Microstructure on Moisture-induced Embrittlement of L12 Intermetallic Compounds

Takasugi

2003

ISIJ International

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The effects of grain size and second phase on moisture-induced embrittlement of L1 2 -type Co 3 Ti and Ni 3 (Si, Ti) alloys were investigated by tensile test in air and vacuum as functions of strain rate and temperature, in combination with microstructural and fractographic observation. In both the intermetallic alloys, brittle-ductile transition (BDT) strain rate defined from an elongation vs. strain rate curve decreased with decreasing grain size, meaning that fine-grained microstructure has the effect of reducing the moisture-induced embrittlement. Also, it was found that dispersion of Co solid solution phase and Nb-containing second phase has the effect of reducing moisture-induced embrittlement of the Co 3 Ti and the Ni 3 (Si, Ti)-Nb alloys, respectively, when their second phases are incoherent with the L1 2 matrix. Contrarily, finely precipitated Co solid solution phase that is coherent with the L1 2 matrix has the effect of enhancing moisture-induced embrittlement of the Co 3 Ti alloys. Mechanisms responsible for the microstructural effect on the moisture-induced embrittlement of the L1 2 intermetallic alloys were presented and discussed.

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Environmental effect on mechanical properties of TiAl base alloys

Cited by 44 publications

References 19 publications

Effect of microstructure on environmental embrittlement in a TiAl base alloy

Effect of microstructure on environmental embrittlement in a TiAl base alloy

Tensile Properties of TiAl Based Alloy in a Gaseous Hydrogen Atmosphere in a Temperature Range from Room Temperature to 973 K

Effect of Microstructure on Moisture-induced Embrittlement of L12 Intermetallic Compounds

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