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The High-Temperature Oxidation of Nb-40Ti-15Al and the Effect of Cr Alloying and Silicide Diffusion Coatings

Published online by Cambridge University Press:  22 February 2011

B. V. Cockeram ,
H. J. Schmutzler ,
J. Shyue ,
K. Hoshino ,
S. Meng ,
R. Wheeler  and
H. L. Fraser
B. V. Cockeram
Affiliation:
Dept. of Materials Science and Engineering, The Ohio State University, Columbus, OH, 43210
H. J. Schmutzler
Affiliation:
Dept. of Materials Science and Engineering, The Ohio State University, Columbus, OH, 43210
J. Shyue
Affiliation:
Dept. of Materials Science and Engineering, The Ohio State University, Columbus, OH, 43210
K. Hoshino
Affiliation:
Dept. of Materials Science and Engineering, The Ohio State University, Columbus, OH, 43210
S. Meng
Affiliation:
Dept. of Materials Science and Engineering, The Ohio State University, Columbus, OH, 43210
R. Wheeler
Affiliation:
Dept. of Materials Science and Engineering, The Ohio State University, Columbus, OH, 43210
H. L. Fraser
Affiliation:
Dept. of Materials Science and Engineering, The Ohio State University, Columbus, OH, 43210
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Abstract

The high-temperature oxidation resistance of Nb-40Ti-15Al-(0 or 5)Cr alloys has been studied. The kinetics and activation energy for the isothermal oxidation of Nb-40Ti-15Al are similar to pure titanium. Detailed TEM analysis of the oxidized Nb-40Ti-15Al alloy reveals that oxygen dissolution has produced a case layer by the decomposition of the matrix B2 phase into oxygen saturated alpha-Ti and an A15 phase. Internal oxidation of the A15 phase to form AlNbO4 occurred in the case layer near the scale/metal interface. The phase separated case layer evolved into a segregated oxide layer containing a co-continuous TiO2 phase. These morphologies of the oxide scale and case layer correlate well with the kinetic data, and suggest that oxygen dissolution in α-Ti and diffusion through TiO2 control the high-temperature oxidation rates. The Cr additions reduced the thickness of the case layer and slowed the oxidation kinetics, but did not change the mechanism. In addition, excellent cyclic oxidation resistant was provided by the silicide diffusion coatings.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 364: Symposium L – High-Temperature Ordered Intermetallic Alloys–VI , 1994 , 1327
Copyright
Copyright © Materials Research Society 1995

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