Abstract
The decomposition of the transition rhombohedral α′R-phase at the temperatures between 85 and 250 °C was investigated by transmission electron microscopy and by X-ray diffraction on single crystals. Below 161 °C the direct decomposition of α′R-phase into the equilibrium hexagonal β-phase without the formation of the transition cubic α′-phase was found. Both transformation sequences α′R → β and α/′R→α′ → β were observed in the temperature range from 161 to 180 °C whereas only the previously known sequence α′R → α′ → β was detected on ageing the alloy between 180 and 250 °C. The precipitation process at the temperatures from 161 to 180 °C is characterized by the decomposition of α′R-phase into the equilibrium β-phase prior to the formation of the transition α′-phase and by the increased rate of decomposition of α′-precipitate.
The observed transformation processes are related to the variation of strains at the partially coherent interface between α′R-phase and α-matrix with the temperature in correlation with the metastable α′R-phase boundary. These considerations allowed to estimate the relative stabilities of precipitated phases and their activation energies of formation and thus to discuss the decomposition mechanism of α′R-phase at various temperatures.
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In conclusion we would like to express our thanks to Doc. Dr. V.Syneček C.Sc. for his valuable discussion. We are also indebted to Ing. V.Šíma for the preparation of used samples, to Mr. Z.Šikýř for his help in X-ray diffraction measurements and to Mr. P.Vyhlídka for the careful chemical analyses of the investigated alloys.
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Simerská, M., Bartuška, P. On the decomposition of the transition rhombohedral phase in the Al-30 wt.% Zn alloy. Czech J Phys 24, 77–84 (1974). https://doi.org/10.1007/BF01596447
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DOI: https://doi.org/10.1007/BF01596447