Abstract
The kinetics of the growth of intermediate phase layers in the aluminum-niobium system has been studied in the temperature range 1000–1500 °C by growing aluminide coatings on niobium by hot-dipping or pack cementation and annealing some of these coatings in an argon atmosphere. The growth of NbAl 3, Nb 2Al and Nb 3Al was observed from 1000 °C to 1400 °C for the first phase and from 1200 °C to 1500 °C for the others. From the kinetics the variation of the diffusion coefficient as a function of temperature was deduced for each phase and shown to obey an Arrhenius type law. The activation energies were found to be 26,57 and 86 kcal mol −1 respectively for the diffusion coefficient in NbAl 3, Nb 2Al and Nb 3Al. By using the concentration profile determined with an electronic micro-beam in Nb 2Al, it was possible to obtain the curve giving the variation of the diffusion coefficient in this compound as a function of the concentration. The diffusion mechanism was elucidated in the case NbAl 3 where it was shown that only the Al atoms diffuse.
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