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The phase equilibria,diffusion growth and diffusivities in the Ni-Al-Pt system at 1 150,1 200 and 1 250℃were studied using Pt/β-NiAl diffusion couples.Based on the measured concentration profiles coupled with the local equilibrium hypothesis,the tie-lines between neighboring phases were determined.Two intermediate phases,Pt_3Al andα-NiPt(Al),are found to develop between the Pt andβ-NiAl couples.The thicknesses of Pt_3Al andα-NiPt(Al) layers varies linearly with the square of annealing time, indicating that the growth of Pt_3Al andα-NiPt(Al) are diffusion-controlled.The calculated Arrhenius equations of the parabolic growth constants,k,for the Pt_3Al andα-NiPt(Al) phases are obtained,respectively.The average ternary inter-diffusivities of the Pt_3Al andβ-NiAl phases at different temperatures are determined from an integration of inter-diffusion fluxes calculated directly from the experimental concentration profiles.
The phase equilibria, diffusion growth and diffusivities in the Ni-Al-Pt system at 1 150,1 200 and 1 250 ° C were studied using Pt / β-NiAl diffusion couples. Based on the measured concentration profiles coupled with the local equilibrium hypothesis, The tie-lines between neighboring phases were determined. Two intermediate phases, Pt_3Al andα-NiPt (Al), are found to develop between the Pt andβ-NiAl couples. The thicknesses of Pt_3Al andα-NiPt (Al) layers vary linearly with the square of annealing time, indicating that the growth of Pt_3Al and α-NiPt (Al) are diffusion-controlled. The calculated Arrhenius equations of the parabolic growth constants, k, for the Pt_3Al andα-NiPt (Al) ternary inter-diffusivities of the Pt_3Al and β-NiAl phases at different temperatures are determined from an integration of inter-diffusion fluxes calculated directly from the experimental concentration profiles.