Hostname: page-component-586b7cd67f-rdxmf Total loading time: 0 Render date: 2024-11-24T12:11:04.344Z Has data issue: false hasContentIssue false
  • English
  • Français

Analyses of Eutectoid Phase Transformations in Nb–Silicide In Situ Composites

Published online by Cambridge University Press:  01 August 2004

B.P. Bewlay ,
S.D. Sitzman ,
L.N. Brewer  and
M.R. Jackson
B.P. Bewlay
Affiliation:
General Electric Global Research, Schenectady, NY 12301, USA
S.D. Sitzman
Affiliation:
HKL Technology, Inc., Pasedena, CA 91104, USA
L.N. Brewer
Affiliation:
General Electric Global Research, Schenectady, NY 12301, USA
M.R. Jackson
Affiliation:
General Electric Global Research, Schenectady, NY 12301, USA
Get access

Abstract

Nb–silicide in situ composites have great potential for high-temperature turbine applications. Nb–silicide composites consist of a ductile Nb-based solid solution together with high-strength silicides, such as Nb5Si3 and Nb3Si. With the appropriate addition of alloying elements, such as Ti, Hf, Cr, and Al, it is possible to achieve a promising balance of room-temperature fracture toughness, high-temperature creep performance, and oxidation resistance. In Nb–silicide composites generated from metal-rich binary Nb-Si alloys, Nb3Si is unstable and experiences eutectoid decomposition to Nb and Nb5Si3. At high Ti concentrations, Nb3Si is stabilized to room temperature, and the eutectoid decomposition is suppressed. However, the effect of both Ti and Hf additions in quaternary alloys has not been investigated previously. The present article describes the discovery of a low-temperature eutectoid phase transformation during which (Nb)3Si decomposes into (Nb) and (Nb)5Si3, where the (Nb)5Si3 possesses the hP16 crystal structure, as opposed to the tI32 crystal structure observed in binary Nb5Si3. The Ti and Hf concentrations were adjusted over the ranges of 21 to 33 (at.%) and 7.5 to 33 (at.%) to understand the effect of bulk composition on the phases present and the eutectoid phase transformation.

Keywords

niobiumsilicidecompositehigh temperaturecreeptI32tP32hP16
Type
Materials Applications
Information
Microscopy and Microanalysis , Volume 10 , Issue 4 , August 2004 , pp. 470 - 480
Copyright
© 2004 Microscopy Society of America

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

Bewlay, B.P., Bishop, R.R., & Jackson, M.R. (1998). The Nb-Ti-Si ternary phase diagram: Determination of solid state phase equlibria in Nb and Ti rich alloys. J Phase Equil 19, 577–586.Google Scholar
Bewlay, B.P., Bishop, R.R., & Jackson, M.R. (1999a). The Nb-Hf-Si ternary phase diagram: Liquid–solid phase equilibria in Nb and Hf rich alloys. Z Metallkunde 90, 413–422.Google Scholar
Bewlay, B.P., Bishop, R.R., & Sutliff, J.A. (1999b). Evidence for the existence of Hf5Si3. J Phase Equil 20, 109–112.Google Scholar
Bewlay, B.P., Jackson, M.R., & Gigliotti, M.F.X. (2001). Single crystals and directionally solidified in situ composites for high-temperature applications. In Intermetallic Compounds—Principles and Practice, Fleischer, R.L. & Westbrook, J.H. (Eds.), Vol. 3, pp. 541–560. New York: John Wiley.
Bewlay, B.P., Jackson, M.R., & Lipsitt, H.A. (1996). The balance of mechanical and environmental properties of a multi-element niobium–niobium silicide based in situ composite. Metall Mater Trans A 27, 3801–3808.Google Scholar
Bewlay, B.P., Jackson, M.R., & Lipsitt, H.A. (1997). The Nb-Ti-Si ternary phase diagram: Evaluation of liquid-solid phase equilibria in Nb and Ti-rich alloys. J Phase Equil 18, 264–278.Google Scholar
Bewlay, B.P., Jackson, M.R., & Subramanian, P.R. (1999c). Processing of high-temperature refractory metal silicide in situ composites. J Metals 51, 32–36.Google Scholar
Bewlay, B.P., Whiting, P., Davis, A.W., & Briant, C.L. (1999d). Creep mechanisms in niobium–silicide based in situ composites. In MRS Proceedings on High Temperature Ordered Intermetallic Alloys VIII (Vol. 552), pp. KK6.11.1–KK6.11.5. Warrendale, PA: Materials Research Society.
Daams, J.L.C., Villars, P., & Van Vucht, J.H.N. (1991). Atlas of Crystal Structure Types for Intermetallic Phases. Materials Park, OH: ASM International.
Gokhale, A.B. & Abbaschian, G.J. (1989). The Hf-Si system. Bull Alloy Phase Diag 10, 390–393.Google Scholar
Grylls, R.J., Bewlay, B.P., Lipsitt, H.A., & Fraser, H.L. (2001). Characterisation of silicide precipitates in Nb-Si and Nb-Ti-Si alloys. Phil Mag A 81, 1967–1978.Google Scholar
Massalski, T.B. (1991). Binary Alloy Phase Diagrams. Metals Park, OH: ASM.
Mendiratta, M.G. & Dimiduk, D.M. (1991). Phase relations and transformation kinetics in the high Nb region of the Nb-Si system. Scripta Metall Mater 25, 237–242.Google Scholar
Mendiratta, M.G. & Dimiduk, D.M. (1993). Strength and toughness of a Nb-Nb5Si3 composite. Metall Mater Trans A 24, 501–504.Google Scholar
Schlesinger, M.E., Okamoto, H., Gokhale, A.B., & Abbaschian, R. (1993). The Nb-Si (niobium-silicon) system. J Phase Equil 14, 502–509.Google Scholar
Subramanian, P.R., Mendiratta, M.G., Dimiduk, D.M., & Stucke, M.A. (1997). Advanced intermetallic alloys—Beyond gamma titanium aluminides. Mater Sci Eng A 239–240, 1–13.Google Scholar
Zhao, J.-C., Bewlay, B.P., & Jackson, M.R. (2001). Determination of Nb-Hf-Si phase equilibria. Intermetallics 9, 681–689.Google Scholar