Nucleation of stoichiometric compounds from liquid: Role of the kinetic factor

The nucleation rate depends on the free-energy barrier and the kinetic factor. While the role of the free energy barrier is a text-book subject, the importance of the kinetic factor is frequently underestimated. In this study, we applied the mean first-passage time method, to obtain the free-energy landscape and kinetic factor directly from the molecular dynamics (MD) simulations of the nucleation of the face-centered cubic (fcc) phase in the pure Ni and the B2 phases in the N i 50 A l 50 and C u 50 Z r 50 alloys. The obtained data show that while the free-energy barrier for nucleation is higher in pure Ni the nucleation rate is considerably lower in the N i 50 A l 50 alloy. This result can be explained by the slow attachment kinetics in the N i 50 A l 50 alloy, which was related to the ordered nature of the B2 phase. Even smaller fraction of the antisite defects in the C u 50 Z r 50 alloy leads to such a slow attachment kinetics that the nucleation is never observed for this alloy in the course of the MD simulation. This is consistent with the experimental facts that the C u 50 Z r 50 alloy is a good glass forming alloy and the N i 50 A l 50 alloy is not. Thus the present study demonstrates that the atom attachment rate can be the critical factor that controls the nucleation process under certain conditions. Disciplines Condensed Matter Physics | Engineering Physics | Materials Science and Engineering Authors Huajing Song, Yang Sun, Feng Zhang, Cai-Zhuang Wang, Kai-Ming Ho, and Mikhail I. Mendelev This article is available at Iowa State University Digital Repository: https://lib.dr.iastate.edu/ameslab_manuscripts/116 PHYSICAL REVIEW MATERIALS 2, 023401 (2018) Nucleation of stoichiometric compounds from liquid: Role of the kinetic factor H. Song,1 Y. Sun,1 F. Zhang,1 C. Z. Wang,1 K. M. Ho,1,2,3 and M. I. Mendelev1 1Division of Materials Sciences and Engineering, Ames Laboratory (US Department of Energy), Ames, Iowa 50011, USA 2Department of Physics, Iowa State University, Ames, Iowa 50011, USA 3Hefei National Laboratory for Physical Sciences at the Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China (Received 2 November 2017; published 20 February 2018) The nucleation rate depends on the free-energy barrier and the kinetic factor. While the role of the free energy barrier is a text-book subject, the importance of the kinetic factor is frequently underestimated. In this study, we applied the mean first-passage time method, to obtain the free-energy landscape and kinetic factor directly from the molecular dynamics (MD) simulations of the nucleation of the face-centered cubic (fcc) phase in the pure Ni and the B2 phases in the Ni50Al50 and Cu50Zr50 alloys. The obtained data show that while the free-energy barrier for nucleation is higher in pure Ni the nucleation rate is considerably lower in the Ni50Al50 alloy. This result can be explained by the slow attachment kinetics in the Ni50Al50 alloy, which was related to the ordered nature of the B2 phase. Even smaller fraction of the antisite defects in the Cu50Zr50 alloy leads to such a slow attachment kinetics that the nucleation is never observed for this alloy in the course of the MD simulation. This is consistent with the experimental facts that the Cu50Zr50 alloy is a good glass forming alloy and the Ni50Al50 alloy is not. Thus the present study demonstrates that the atom attachment rate can be the critical factor that controls the nucleation process under certain conditions. DOI: 10.1103/PhysRevMaterials.2.023401