Abstract
Based on the pair distribution function g(r), molecular dynamics simulations on NiAl and Ni3Al melts were carried out to investigate the relationships between self-diffusion coefficient and viscosity. The self-diffusion coefficients of Ni in melts and the viscosity of melts were calculated using the Einstein relation and Green-Kubo equation, respectively. Our result shows that there is a crossover in the self-diffusion coefficient and viscosity from high-temperature Arrhenius behavior to low-temperature non-Arrhenius behavior, and the crossover is accompanied by the breakdown of Stokes-Einstein relation (SER) and the onset of fractional Stokes-Einstein relation. The breakdown temperature of SER is nearly twice the glass-transition temperature and much higher than the mode-coupling critical temperature for both NiAl and Ni3Al melts. Further analyses based on g(r) suggest that temperature dependences of the pair correlation entropy and the partial pair correlation entropy of components may be used as probes for testing the validity of Stokes-Einstein relation and predicting its breakdown temperature.
Highlights
In order to study the diffusive motion of a mesoscopic sphere in a viscous medium, the well-known Stokes-Einstein relation (SER) was derived as Dη 1⁄4 kBT 6πr (1)where D and η refer to the self-diffusion coefficient and viscosity, respectively
Based on the pair distribution function g(r), molecular dynamics simulations on NiAl and Ni3Al melts were carried out to investigate the relationships between self-diffusion coefficient and viscosity
The equiplibffiffirffiiffiffiuffiffimffiffiffiffiffiffimffiffi elting temperatures are calculated by Tm 1⁄4 TÀ þ Tþ À (TþTÀ), and the data are listed in Table I together with experimental results for comparison
Summary
In order to study the diffusive motion of a mesoscopic sphere in a viscous medium, the well-known Stokes-Einstein relation (SER) was derived as. Studies show that the rapid increase of dynamical heterogeneity will lead to a marked change of the ratio of the self-diffusion coefficients of components, and the ratio can be used to predict TSE of the SER.. The coordinates of all the atoms in the system are required to get the structural parameters mentioned above.12–16 Because it is directly measurable by experiment, but probably more so due to the fact that various properties of materials can be estimated from it, the pair distribution function g(r) plays a central role in the physics of liquids. NiAl and Ni3Al, as typical representatives of Ni-based superalloys, are selected to assess the relationships between the self-diffusion coefficient and viscosity for liquid alloys based on the pair distribution function
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