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L. Qin, A. Redermeier, E. Kozeschnik:
"Analysis of composition and shape of critical copper nuclei in dilute Fe-Cu alloys from atomistic simulations";
Talk: EUROMAT 2017, THESSALONIKI; 2017-09-17 - 2017-09-22.

The aim of this work is to identify the critical size of early-stage bcc Cu precipitates in Fe-Cu alloys and provide information about shape and composition of the clusters at the critical size from atomistic simulations. The nucleation process is reproduced by Monte Carlo simulations with an interatomic potential depending on the Local Chemical Environment approach. Combined with an Umbrella Sampling technique, the nucleation free energy is evaluated for each supersaturated condition and the critical size is recognized as the size corresponding to the highest point on free energy curve. The concentration profiles of Cu nuclei in critical size indicate that a certain amount of Fe atoms (~20a.t.%) are present in first-formed precipitates at low temperature, whereas at higher temperature, Cu nuclei are almost pure Cu. Moreover, the shape analysis of pre-critical clusters shows that clusters with less than 30 Cu atoms adopt a very irregular shape, and this irregularity can cause a severe underestimation of the nucleation energy barrier with the spherical cluster assumption.