Aluminum diffusion in aluminide coatings deposited by the CVD method on pure nickel

The aluminum diffusion in aluminide coatings deposited on nickel by the CVD method was investigated. The microstructure, chemical and phase compositions of coatings were examined by SEM, EDS and XRD techniques. The triple zone structure was revealed. The beta-NiAl phase was on the surface of the coatings, whereas gamma-(Ni) and gamma'-Ni3Al formed deeper parts of the coatings. Diffusion coefficients were calculated from the concentration profiles in coatings deposited for various times (15 min, 1 h, 4 h and 8 h) at 1000 degrees C and 1050 degrees C. The procedure was based on the classic finite difference method (FDM). Diffusion coefficients in three phases were calculated simultaneously and the influence of diffusivity in one phase on the diffusivity in the neighboring phase was taken into account. The results of the calculation agree with the literature data obtained for each of the analyzed phases separately. (C) 2013 Elsevier Ltd. All rights reserved.