Development of ultrafine lamellar structures in two-phase {gamma}-TiAl alloys
- Oak Ridge National Lab., TN (United States)
Processing of two-phase {gamma}-TiAl alloys above the {alpha}-transus temperature (T{sub a}) produced unique refined-colony/ultrafine lamellar structures in both powder- and ingot-metallurgy (PM and IM, respectively) alloys. These ultrafine lamellar structures consist of fine laths of the {gamma} and {alpha}{sub 2} phases, with average interlamellar spacings ({lambda}{sub L}) of 100 to 200 nm and {alpha}{sub 2}-{alpha}{sub 2} spacings ({lambda}{sub {alpha}}) of 200 to 500 nm, and are dominated by {gamma}/{alpha}{sub 2} interfaces. This characteristic microstructure forms by extruding PM Ti-47Al-2Cr-2Nb alloys at 1,400 C and also forms with finer colony size but slightly coarser, fully lamellar structures by hot-extruding similar IM alloys. Alloying additions of B and W refine {lambda}{sub L} and {lambda}{sub {alpha}} in both IM Ti-47A (cast and heat treated at 1,400 C) and IM Ti-47Al-2Cr-2Nb alloys (extruded at 1,400 C). The ultrafine lamellar structure in the PM alloy remains stable during heat treatment at 900 C for 2 hours but becomes unstable after 4 hours at 982 C; the ultrafine lamellar structure remains relatively stable after aging for > 5,000 hours at 800 C. Additions of B + W dramatically improve the coarsening resistance of {lambda}{sub L} and {lambda}{sub {alpha}} in the IM Ti-47Al alloys aged for 168 hours at 1,000 C. In both the PM and IM 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 a} in IM TiAl alloys and stabilize such structures during heat treatment or aging.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC05-96OR22464
- OSTI ID:
- 605814
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Journal Name: Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science Journal Issue: 1 Vol. 29; ISSN MMTAEB; ISSN 1073-5623
- Country of Publication:
- United States
- Language:
- English
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