On the diffusion of carbon in titanium carbide

Abstract

The chemical diffusion coefficient of carbon in TiC_1-y was determined as a function of stoichiometry and temperature in the range between 1000 and 1600°C using the diffusion couple technique. In marker experiments carbon was found to be virtually the only diffusing component. Accurate carbon analyses were performed using EPMA, both in diffusion couples and in the carbides present in equilibrated alloys. The homogeneity region of TiC_1-y in this temperature range and the concentration profiles were accurately determined. From these profiles it is immediately clear that the diffusivity of carbon is a function of the carbon concentration. The interdifussion coefficient {$\tilde D$} increases with decreasing carbon concentration and can be expressed by; {

$$\tilde D(TiC_{t - y} ) = [0.48{\text{ exp(9}}{\text{.2}}y)] exp --\left( {\frac{{39500}}{T}} \right){\text{ cm}}^{\text{2}} /s$$

} A number of often conflicting results have been published on diffusion in titanium carbide. It is shown that nearly all reported values can be fitted within the range found in the present work, in which the marked variation of {$\tilde D$} with carbon content is taken into account. Comparison between the interdiffusion coefficient {$\tilde D$} and the tracer diffusion coefficientD ^*_c is difficult because of uncertainties in the thermodynamic factor.