Abstract
Discontinuous precipitation (DP) occurs in many alloy systems under certain conditions. It is called discontinuous precipitation because precipitation occurs on prior matrix grain boundaries followed by grain boundary movement. The DP nodule consists of alternate lamellae of the precipitate and the matrix respectively. The chemical driving force for DP is one of solute supersaturation. Although solute supersaturation is responsible for precipitation, it has to be coupled with another driving force to explain grain boundary migration. This coupling driving force has been identified to be diffusional coherency strain which has been verified to be active in diffusion induced grain boundary migration and liquid film migration.
To test diffusional coherency strain theory for discontinuous precipitation Mg-7Al and Mg-7Al-1Pb alloys were studied. While the fraction transformed was high at 6% in Mg-7Al alloy, dit was significantly low at 2% in Mg-7Al-1Pb alloy. The velocity of DP nodules decreased by half in alloy with Pb as compared to the alloy without Pb. Theoretical calculations also predict that the misfit parameter δth decreases with the addition of Pb. These observations are an evidence to the fact that diffusional coherency strain is the most active driving force for the movement of the grain boundaries of the DP nodules during discontinuous precipitation in Mg-Al alloy.
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References
Baik Y J and Yoon D N 1986Acta Metall. 34 2039
Baluffi R W and Cahn J W 1981Acta Metall. 29 493
Chung Y H, Shin M C and Yoon D W 1992Acta Metall. 40 2177
Fournelle R A and Clark J B 1972Metall. Trans. 3 2757
Hillert M and Purdy G R 1978Acta Metall. 26 333
Hillert M 1983Scr. Metall. 17 237
Meyrick G 1976Scr. Metall. 10 649
Pearson W B 1958A handbook of lattice spacings and structures of metals and alloys (New York: Pergamon Press) {vd2} p. 1967
Rhee W H, Song Y D and Yoon D W 1987Acta Metall. 35 57
Smithels Metals Reference Book 1983 (UK: Butterworths) 6th ed. pp 11–333
Sulonen M S 1960Acta Metall. 8 669
Sulonen M S 1964Acta Metall. 12 748
Yoon D N and Hupman W S 1981Acta Metall. 27 973
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Kashyap, K.T., Ramachandra, C., Sujatha, M. et al. Role of diffusional coherency strain theory in the discontinuous precipitation in Mg-Al alloy. Bull Mater Sci 23, 39–45 (2000). https://doi.org/10.1007/BF02708610
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DOI: https://doi.org/10.1007/BF02708610