The thermal stability of the microstructure of {gamma}-based titanium aluminides
- Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.
The thermal stability of the microstructure of {gamma}-based titanium aluminides after aging at elevated temperatures was studied by transmission and analytical electron microscopy (TEM and AEM, respectively) as well as by optical microscopy. Predominantly lamellar microstructures of Ti-47Al (at.%), Ti-47Al+B (140appm) and Ti-47Al+B+W (0.5at.%) alloys were produced by heat-treatment at 1,400 C for 1h followed by furnace cooling. The average lamellar spacing of the as-heat treated was measurably finer in both alloys with solute additions (400 nm in Ti-47Al, 170--190nm in alloys modified with B or W+B). The {alpha}{sub 2} lamellae were especially finely distributed and continuous in the Ti-47Al+W+B alloy. These alloys were then aged at 800, 1,000 or 1,200 C for 168h. The alloys aged at 800 C did no show much change, whereas aging at 1,000 C produced significant lamellar break-up and coarsening in the Ti-47Al and B-modified alloys, but not much change in the alloy modified with W+B. In addition, coarsening by grain boundary migration led to the formation of new coarser, irregular and branched lamellae. Aging for 168h at 1,200 C significantly degraded the originally fine lamellar structure. In addition to the lamellar degradation processes observed at 800--1,000 C, spheroidized precipitates of {alpha}{sub 2} and {gamma} were also observed at 1,200 C. The effect of alloying additions of B and W to the binary alloy is to refine the initial lamellar structure produced by heat-treatment at 1,400 C, and then to stabilize that original lamellar structure (particularly B+W) during subsequent aging at 800--1,000 C.
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 264087
- Journal Information:
- Acta Materialia, Vol. 44, Issue 7; Other Information: PBD: Jul 1996
- Country of Publication:
- United States
- Language:
- English
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