Morphological Evolution of Fe-Rich Precipitates in a Cu-2.0Fe Alloy During Isothermal Treatment
The morphology of precipitates changes during coarsening regimes,thereby resulting in the modification of mechanical properties of metallic materials.Hence,understanding the morphological evolution in precipitates is critical to tailor the macroscopic properties of industrial alloys.In particular,the morphology of Fe-rich precipitates in Cu alloys is complex,and it evolves from sphere to cube to petal and finally splits,which has been observed during casting and furnace cooling.However,morphological changes in Fe-rich precipitates during isothermal treatment remain unclear;thus,revealing the mecha-nism of morphological evolution is necessary.In this study,the relationship among the morphological evo-lution behavior of Fe-rich precipitates in Cu-2.0Fe(mass fraction,%)alloy,temperature,and time under different isothermal-treated processes was analyzed using SEM and TEM coupled with phase-field mod-eling.Results show morphology changes from a sphere in nanoscale to a cube in submicron scale to a four-branched petal in the submicron scale,and to a multi-branched petal in micron scale during coarsen-ing of Fe-rich precipitates in Cu-2.0Fe alloy isothermally treated at 924,964,and 984℃(i.e.,the temper-ature range of the fcc Fe phase).The size of multi-branched petal-like Fe-rich precipitates and the num-ber of branches increase with the increase of isothermal temperature and holding time.During coarsen-ing of multi-branched petal-like precipitates,the surrounding small Fe-rich precipitates are engulfed,and thence the number density of the smaller ones in nano and submicron scales decreases when the tem-perature increases.The modeling result elucidates the multiple morphological evolution of Fe-rich precipi-tates,which is identical to the experiments,under the effects of interfacial energy,elastic energy,and chemical driving force.In particular,the combined effect of the latter two energies induces the initiation and growth of secondary branches out of primary branches in the four-branched petals,thereby produc-ing multi-branched petal-like precipitates.
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