Interdiffusion in the carbides of the Nb-C system |
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Authors: | J Woodford Y A Chang |
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Affiliation: | (1) Materials Science and Engineering Department, University of Wisconsin-Madison, 53706 Madison, WI |
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Abstract: | Interdiffusion coefficients in Nb2C and NbC1−x were measured using bulk diffusion couples in the temperature range from 1400 °C to 1700 °C. Marker experiments were used
to show that carbon is the only component undergoing significant diffusion in both carbides. Carbon concentrations were measured
by difference using electron probe microanalysis, and interdiffusion coefficients were taken from Boltzmann-Matano analyses
of the resulting concentration profiles. This analysis clearly showed that, in NbC1−x, interdiffusion coefficient varies with carbon concentration, and is expressed by where x is the site fraction of vacancies on the carbon sublattice. The interdiffusion coefficient in Nb2C is given by Parabolic layer growth coefficients were estimated from the Nb|C diffusion couples as well. They are given by The value of
in NbC1−x was found to be consistent with literature values for the tracer diffusivity of C in NbC1−x
via the thermodynamic factor, which was determined in two ways. |
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