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High temperature oxidation protection of Ti3Al-based alloys with different Nb-content by a combined Al-/F-treatment

Published online by Cambridge University Press:  19 December 2014

A. Donchev ,
M. Galetz  and
M. Schütze
A. Donchev
Affiliation:
DECHEMA-Forschungsinstitut, D-60486 Frankfurt am Main/Germany
M. Galetz
Affiliation:
DECHEMA-Forschungsinstitut, D-60486 Frankfurt am Main/Germany
M. Schütze
Affiliation:
DECHEMA-Forschungsinstitut, D-60486 Frankfurt am Main/Germany
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Abstract

Orthorhombic titanium-based Ti2AlNb alloys cannot be used above a temperature limit of about 800°C due to accelerated oxidation and environmental embrittlement. This embrittlement is caused by the high oxygen solubility which deteriorates the mechanical properties. Even if these materials possess an Al content up to ca. 25at.% no protective alumina layer is formed. Instead a non-protective fast growing mixed scale is found. Several attempts have been made to increase their operation temperature e.g. by coatings but none has proven sufficiently protective so far. One new way presented in this paper is to enrich Al in a narrow surface zone by using a powder pack process (aluminization) followed by a fluorination step. Exposure tests at elevated temperature have shown that the aluminized specimens form an alumina layer during exposure in oxidizing environments. Due to the gradient in the Al-concentration interdiffusion with the substrate and the Al-rich diffusion zone occurs which lowers the Al concentration in the diffusion zone. If the Al content drops below a critical value, Ti oxides will also form, which deteriorates the protection provided by the alumina scale. The subsequent fluorination triggers the fluorine effect which stabilizes the protective alumina layer. Untreated specimens are covered with a thick non protective scale and exhibit oxygen ingress in the subsurface zone while treated specimens reveal a thin protective alumina layer and no inward diffusion of oxygen. In this paper results of exposure tests of untreated and treated orthorhombic Ti2AlNb alloys will be presented and compared with the Nb-free α2-phase Ti3Al and Nb-containing Ti3Al-based alloys.

Keywords

coatingoxidationthermogravimetric analysis (TGA)
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1760: Symposium YY – Advanced Structural and Functional Intermetallic-Based Alloys , 2015 , mrsf14-1760-yy07-05
Copyright
Copyright © Materials Research Society 2014 

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References

REFERENCES

Kumpfert, J., Leyens, C., Titanium and Titanium alloys, ed. Leyens, C., Peters, M. (WILEY-VCH, 2003) pp. 59–88.Google Scholar
Ralison, A.. Dettenwanger, F., Schütze, M., Materials and Corrosion 51, 317–328 (2000).3.0.CO;2-W>CrossRefGoogle Scholar
Leyens, C., Titanium and Titanium alloys, ed. Leyens, C., Peters, M. (WILEY-VCH, 2003) pp. 187–230.Google Scholar
Donchev, A., Gleeson, B., Schütze, M., Intermetallics 11, 387–398 (2003).CrossRefGoogle Scholar
Schumacher, G., Thesis (RWTH Aachen, 2001) pp. 43–44.Google Scholar
Bianco, R., Rapp, R.A., Jacobson, N.S., Oxid. Metals. 38, 33–43 (1992).CrossRefGoogle Scholar
Donchev, A., Schütze, M., Mat. Sci. Forum 638-642, 1294–1299 (2010).CrossRefGoogle Scholar
Smialek, J.L., Nesbitt, J.A., Brindley, W.J., Brady, M.P., Doychak, J., Mater. Res. Soc. Proc. 364, Pittsburgh, PA (1995) pp. 1273–1284.Google Scholar
Zhang, M.-X., Hsieh, K.C., DeKock, J., Chang, Y.A., Scripta Metall. Mater. 27, 1361–1366 (1992).CrossRefGoogle Scholar
Lee, E.U., Waldmann, H., Scripta Metall. 22, 1389–1394 (1988)CrossRefGoogle Scholar
Donchev, A., Schütze, M., Möller, W., Yankov, R., Structural aluminides for elevated temperatures, ed. Kim, Y.W., Morris, D., Yang, R., Leyens, C. (TMS, 2008) pp. 323–332.Google Scholar