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Temporal Evolution of Bimodal Distribution of γ’ Precipitates in Ni-Al-Mo Alloys under the Influence of Coherency Strains

  • A.D. Sequeira (a1), H.A. Calderon (a2) and G. Kostorz (a3)

Abstract

The influence of coherency strains produced by the γ-γ’ lattice mismatch, δ, on the decomposition process of Ni-Al-Mo alloys with a bimodal size distribution is presented. Samples with δ ranging from positive to negative, were investigated in a double-step aging procedure. The evolution of the microstructure and the kinetics of coarsening were studied using transmission electron microscopy (TEM). The lattice mismatch between the matrix and the different classes of precipitates was determined by high-resolution high-temperature x-ray diffraction. It is shown that the strain fields produced by the lattice mismatch can influence dramatically the decomposition of metallic alloys. It is suggested that the reduction of the coarsening rate of the large precipitates, the fast coarsening rate of the small precipitates and the distortions detected in the matrix are all direct consequences of the elastic fields produced by the γ-γ’ lattice mismatch.

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1 Reppich, B., Kühlein, W., Mayer, G., Puppel, D., Schulz, M. and Schumann, G., Mater. Sci. Eng. 83, 45 (1986).
2 Chellman, D. J. and Ardell, A. J., Materials Architecture, edited by Bilde-Sørensen, J.B., Hansen, N., Juul Jensen, D., Leffers, T., Liholt, H., Pedersen, O.B., Proc. Tenth Risø International Symposium on Metallurgy and Materials Science (Risø National Laboratory, Roskilde 1989) p. 295
3 Sequeira, A. D., Calderon, H. A. and Kostorz, G., Scripta Metall. 30, 7 (1994)
4 Sequeira, A. D., Calderon, H. A., Pedersen, J. S. and Kostorz, G., Acta metall. mater. 43, 3427 (1995)
5 Sequeira, A. D., Calderon, H. A., Pedersen, J. S. and Kostorz, G., Acta metall. mater. 43, 3441 (1995)
6 Sequeira, A. D., Effect of Coherency Strains on the Decomposition of Ni-Al- Mo Alloys, Doctoral Dissertation no. 10440, ETH Zurich (1993).

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