The decomposition of alpha phase during continuous cooling and isothermal transformation in gamma titanium aluminide

McQuay, P.; Dimiduk, Dennis M.; Semiatin, S. L.

doi:10.1016/0956-716x(91)90476-h

Cited by 55 publications

(11 citation statements)

References 5 publications

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“…The ␣-phase lamellae that remain during cooling subsequently transform to an ordered ␣ 2 phase at temperatures below the eutectoid temperature. [22,23,24] Nearly identical reaction paths exist in the presence of ␤ phase upon cooling from the ␣ ϩ ␤ field (provided that the ␤-phase volume fraction is small), and these are more common in quaternary and higher-order gamma alloys. [23,25,26] Consequently, as a general method, microstructures were controlled in the present study through the heat-treatment method schematically depicted in Figure 1, which was applied to sections of the recrystallized forged plate.…”

Section: B Microstructuresmentioning

confidence: 97%

“…[22,23,24] Nearly identical reaction paths exist in the presence of ␤ phase upon cooling from the ␣ ϩ ␤ field (provided that the ␤-phase volume fraction is small), and these are more common in quaternary and higher-order gamma alloys. [23,25,26] Consequently, as a general method, microstructures were controlled in the present study through the heat-treatment method schematically depicted in Figure 1, which was applied to sections of the recrystallized forged plate. The figure suggests that there are several important control parameters that influence the grain size and lamellar attributes; these are labeled R 1 through R 4 , H 1 , H 2 , T 1 , T 2 , and T C in Figure 1.…”

Section: B Microstructuresmentioning

confidence: 97%

See 1 more Smart Citation

The role of grain size and selected microstructural parameters in strengthening fully lamellar TiAl alloys

Dimiduk

Hazzledine

Parthasarathy

et al. 1998

Metall Mater Trans A

144

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More than 5 years ago, wrought processing was first used to produce fully lamellar (FL) microstructures in TiAl alloys having grain sizes less than Ϸ400 m. These alloys exhibit an improvement in overall balance of properties, especially at high temperatures. More recently, such microstructural forms led to exceptional yield strengths (500 to 1000 MPa at low temperatures) while maintaining attractive high-temperature properties. The improvements appeared to be related to an unusually high apparent sensitivity of strength to grain size. Studies reported an apparent value for the slope of the Hall-Petch (HP) plot approaching 5 for FL gamma alloys, while that for single-phase or ͌ MPa m duplex microstructures is near unity. The present investigations examine the slope of the HP plot for FL microstructures, paying particular attention to the lamellar microstructural variables. Results show that the ␣ 2 lamellar thickness and spacing and the ␥ lamellar thickness can vary over more than two orders of magnitude with typical process methods. These spacings influence the value of k y in the HP (grain size) relationship. Since they often change concomitantly with grain size in processing, they can give rise to a large scatter in the HP plot. The investigations also examine the flow behavior, glide barriers, and slip multiplicity for polysynthetically twinned (PST) crystals (the single-grain analogue of FL material), and then map this behavior into an explanation of the yield behavior of high-strength FL gamma alloys.

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Section: B Microstructuresmentioning

confidence: 97%

Section: B Microstructuresmentioning

confidence: 97%

The role of grain size and selected microstructural parameters in strengthening fully lamellar TiAl alloys

Dimiduk

Hazzledine

Parthasarathy

et al. 1998

Metall Mater Trans A

144

View full text Add to dashboard Cite

show abstract

“…The occurrence of the latter in a quenched Ti-48 Al alloy has also been confirmed very recently (12). In the second, where a Ti-48AI-2Mn-2Nb alloy was studied (14), very similar effects of cooling rate on the microstructure were reported, and the occurrence of the massive reaction at high cooling rates was confirmed (15). The purpose of this paper is to report on the composition dependence of transformations in Ti-(43-50) Al alloys water quenched from the fully ax region.…”

Section: Introductionmentioning

confidence: 72%

Air Force Engineering Research Initiation Grants (1990-1991)

Freiman¹

1992

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“…This effectively shifts the CCT domains for the lamellar, Widmanstätten-like, and massive gamma microstructures to longer times or slower cooling rates. [31] For the cast alloy, SEM/EDS analysis for current levels of 45, 55, and 65 A shown in Table II revealed that the dendrites, which solidified first, were enriched in chromium or contained chromium contents near that of the overall chromium composition of the alloy. The interdendritic gamma, which solidified last, was depleted in chromium relative to the overall chromium composition.…”

Section: E Sem Analysismentioning

confidence: 98%

Autogenous gas tungsten arc weldability of cast alloy Ti−48Al−2Cr−2Nb (Atomic percent) versus extruded alloy Ti−46Al−2Cr−2Nb−0.9Mo (Atomic percent)

Bharani

Acoff

1998

Metall Mater Trans A

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This study examines procedures for consistently producing sound (crack and void free) welds using the autogenous (without filler metal) gas tungsten arc (GTA) welding process. Cast alloy Ti-48Al-2Cr-2Nb (at. pct) and extruded alloy Ti-46Al-2Cr-2Nb-0.9Mo (at. pct) have been examined to determine if sound welds can be produced using autogenous GTA welding without any preheat. Experimentation consisted of GTA spot welding samples of gamma titanium aluminide at weld current levels of 45, 55, 65, and 75 A for a duration of 3 seconds. For the cast alloy, current levels of 45, 55, and 65 A for 3 seconds produced similar fusion zone microstructures, which consisted of a dendritic solidification structure. The fusion zone microstructure of the 75 A for 3 seconds current level differed significantly from the lower current levels. It also consisted of a dendritic solidification structure; however, the morphology was quite different. For the extruded alloy, current levels of 45 and 55 A for 3 seconds produced fusion zone microstructures similar to the lower current level samples of the cast ␥-TiAl, which consisted of a dendritic solidification structure. The fusion zone microstructures of the 65 and 75 A samples were similar to each other, but they had a dendritic solidification structure of a different morphology than that of the 45 and 55 A samples. For both alloys at all current levels, microhardness profiles showed an increase in hardness from the base metal to the fusion zone. There were no significant differences in the average fusion zone hardness as a function of increasing current level. However, nanoindentation testing did show that certain phases and microconstituents in the fusion zone did have significant variations in hardness in relation to the enrichment and depletion of chromium.

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The decomposition of alpha phase during continuous cooling and isothermal transformation in gamma titanium aluminide

Cited by 55 publications

References 5 publications

The role of grain size and selected microstructural parameters in strengthening fully lamellar TiAl alloys

The role of grain size and selected microstructural parameters in strengthening fully lamellar TiAl alloys

Air Force Engineering Research Initiation Grants (1990-1991)

Autogenous gas tungsten arc weldability of cast alloy Ti−48Al−2Cr−2Nb (Atomic percent) versus extruded alloy Ti−46Al−2Cr−2Nb−0.9Mo (Atomic percent)

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