Effect of quaternary element addition on the oxidation behavior of Ti{sub 3}Al-Nb intermetallics
Alloys based on {alpha}{sub 2}-Ti{sub 3}Al intermetallics are promising materials for many high temperature applications due to their low density and high specific strength. However, low room temperature ductility and inadequate oxidation resistance are of concern for many applications. The addition of Nb is beneficial as it not only improves the room temperature ductility but also helps to improve the oxidation resistance to some extent. But in most cases oxidation resistance is not sufficient even for the alloys with high Nb content. The present work is concerned with the improvement in the oxidation resistance of Ti{sub 3}Al-Nb alloys by the addition of quaternary elements using both the conventional alloying and ion-implantation technique. The oxidation behavior of the three base alloys: Ti-25Al-11Nb, Ti-24Al-20Nb, Ti-22Al-20Nb and their modified versions with Si, Zr and Hf as quaternary addition was investigated at 800 and 900 C in oxygen, oxygen plus water vapor and air. Oxidation behavior differed significantly for these alloys in different environments. It was found that the oxidation rates were higher in oxygen than in air. The oxide scale analysis using optical microscopy, XRD and SEM/EDAX revealed that the scale was a mixture of TiO{sub 2}, Al{sub 2}O{sub 3} and Nb{sub 2}O{sub 5} with the outer layer rich in TiO{sub 2} for the base alloys. However, the low Al containing alloys Ti-24Al-20Nb and Ti-22Al-20Nb with quaternary additions were found to have much lower oxidation rates than the base alloys in all environments. Oxide scale analysis confirmed the formation of an alumina rich scale with some amount of titania and Nb in the case of quaternary alloys. SIMS analysis after two-stage oxidation in {sup 16}O + {sup 18}O mixture was carried out to determine the oxide growth mechanism during oxidation. The beneficial effect of these quaternary additions em be attributed to their ability to enhance alumina formation in the scale, this effect being more pronounced in the case of Si and Zr ion-implanted alloys than for conventional alloying.
- Research Organization:
- Indian Inst. of Technology and Engineering, Bombay (IN)
- OSTI ID:
- 20002622
- Report Number(s):
- CONF-990401-; TRN: IM200002%%622
- Resource Relation:
- Conference: Corrosion NACExpo 99, 54th Annual Conference and Exposition, San Antonio, TX (US), 04/25/1999--04/30/1999; Other Information: 1 CD-ROM. Operating Systems: Windows 3.1, '95, '98 and NT; Macintosh; and UNIX; PBD: 1999; Related Information: In: Corrosion 99: Proceedings, [3500] pages.
- Country of Publication:
- United States
- Language:
- English
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