Development of Ultrafine, Lamellar Structures in Two-Phase {gamma}-TiAl Alloys

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Processing of two-phase gamma-TiAl alloys (Ti-47Al-2Cr-2Nb or minor modifications thereof) above the alpha-transus temperature (T {sub alpha}) produced unique refined-colony/ultrafine lamellar structures in both powder- and ingot-metallurgy (P/M and I/M, respectively) alloys. These ultrafine lamellar structures consist of fine laths of the gamma and alpha {sub 2} phases, with average interlamellar spacings (lambda {sub Lambda}) of 100-200 nm and alpha {sub 2}-alpha {sub 2} spacings (lambda {sub alpha}) of 200-500 nm, and are dominated by gamma/alpha {sub 2} interfaces. This characteristic microstructure forms by extruding P/M Ti-47Al-2Cr-2Nb alloys above T {sub alpha}, and also forms with finer colony size but ... continued below

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42 p.

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Maziasz, P. J. December 1997.

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Processing of two-phase gamma-TiAl alloys (Ti-47Al-2Cr-2Nb or minor modifications thereof) above the alpha-transus temperature (T {sub alpha}) produced unique refined-colony/ultrafine lamellar structures in both powder- and ingot-metallurgy (P/M and I/M, respectively) alloys. These ultrafine lamellar structures consist of fine laths of the gamma and alpha {sub 2} phases, with average interlamellar spacings (lambda {sub Lambda}) of 100-200 nm and alpha {sub 2}-alpha {sub 2} spacings (lambda {sub alpha}) of 200-500 nm, and are dominated by gamma/alpha {sub 2} interfaces. This characteristic microstructure forms by extruding P/M Ti-47Al-2Cr-2Nb alloys above T {sub alpha}, and also forms with finer colony size but slightly coarser fully-lamellar structures by hot-extruding similar I/M alloys. Alloying additions of B and W refine lambda {sub L} and lambda {sub alpha} in both I/M Ti-47Al (cast and heat-treated above T {sub alpha}) or in extruded Ti-47Al-2Cr-2Nb alloys. The ultrafine lamellar structure in the P/M alloy remains stable during heat-treatment at 900 {degrees}C for 2h, but becomes unstable after 4h at 982 {degrees}C; the ultrafine lamellar structure remains relatively stable after aging for {gt}5000 h at 800 {degrees}C. Additions of B+W dramatically improve the coarsening resistance of lambda L and lambda alpha in the I/M Ti-47Al alloys aged for 168 h at 1000{degrees}C. In both the P/M and I/M Ti-47Al-2Cr-2Nb alloys, these refined-colony/ultrafine-lamellar structures correlate with high strength and good ductility at room temperature, and very good strength at high temperatures. While refining the colony size improves the room-temperature ductility, alloys with finer lambda {sub L} are stronger at both room- and high-temperatures. Additions of B+W produce finer as-processed lambda {sub L} and lambda {sub alpha} in I/M TiAl alloys, and stabilize such structures during heat-treatment or aging.

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42 p.

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OSTI as DE97008429

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  • 126. annual meeting of the Minerals, Metals and Materials Society, Orlando, FL (United States), 9-13 Feb 1997; Other Information: DN: Presented at Symposium on Fundamentals of Gamma Titanium Aluminides, 1997TMS Annual Meeting, Orlando, FL.

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  • Other: DE97008429
  • Report No.: CONF-970201--33
  • Grant Number: AC05-96OR22464
  • Office of Scientific & Technical Information Report Number: 621541
  • Archival Resource Key: ark:/67531/metadc690842

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  • December 1997

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  • Aug. 14, 2015, 8:43 a.m.

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  • Jan. 21, 2016, 7:52 p.m.

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Maziasz, P. J. Development of Ultrafine, Lamellar Structures in Two-Phase {gamma}-TiAl Alloys, article, December 1997; Tennessee. (digital.library.unt.edu/ark:/67531/metadc690842/: accessed October 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.