Composition dependence of diffusion and thermotransport in Ni-Al melts: A step towards molecular dynamics assisted databases

Abstract

We present an extensive and self-consistent database of diffusion and thermotransport properties of molecular-dynamics models of Ni-Al melts with an embeddedatom method potential. The database is generated over wide temperature and composition ranges. A careful comparison with available fragmentary experimental data is made to ensure reliability of the employed model description of Ni-Al melts. A comprehensive analysis of the presented data is carried out and the emerging trends are discussed in details. In particular, a phenomenological model for the composition dependence of the enthalpy of mixing is introduced. This model accurately describes our simulation data for Ni-Al melts as well as enables an ease access to the partial enthalpies of species essential for precise characterization of thermotransport. Furthermore, an intriguing similarity between the shapes of the composition dependence of the Manning factor (which characterizes the interrelation between the collective and single-particle diffusion) and the enthalpy of mixing in Ni-Al melts is brought to attention. Meanwhile, our results for the reduced heat of transport (which characterizes the pure heat conduction initiated by collective diffusion in isothermal conditions) allow us to predict that, in Ni-Al melts, Ni and Al tend to migrate, respectively, to the cold and hot ends in the presence of a temperature gradient. Overall, we highlight a great importance of the presented study for developing and testing of theoretical frameworks to enable sophisticated control of the heat and mass transport in binary melts.

Diffusion in Ni–Zr Melts: Insights from Statistical Mechanics and Atomistic Modeling

“…At high temperatures (i.e., in the normal liquid state) the composition dependence of has similar trends to those which were previously observed for Ni-Al melts. [20,26,35,[50][51][52] In particular, as in the case of Ni-Al melts it can be seen in Figure 5 (a) that in the normal liquid state of the models of Ni-Zr melts we have for all compositions as it can be expected for binary liquid alloys with mixing tendency in accordance with our discussion in the previous section. Furthermore, it is generally expected that collective diffusion kinetics in non-demixing binary liquid alloys should slow down upon increasing the concentration of the minority species towards the equi-atomic composition.…”

“…Furthermore, it is generally expected that collective diffusion kinetics in non-demixing binary liquid alloys should slow down upon increasing the concentration of the minority species towards the equi-atomic composition. [20,26,[50][51][52] In accordance with this suggestion, a minimum in the composition dependence of in Figure 5 (a) is located somewhere in the range of . The minimum value of the correction factor for the models of Ni-Zr melts in the normal liquid state is practically independent of temperature and it can be estimated as about 0.67.…”

“…The minimum value of the correction factor for the models of Ni-Zr melts in the normal liquid state is practically independent of temperature and it can be estimated as about 0.67. Again, we should note that the position and depth of the minima in the composition dependencies of for the models of Ni-Zr and Ni-Al melts in the normal liquid state reveal very similar values (see also [20,26] ).…”

“…The methodology of MD simulations, which we advance in this work for Ni-Zr melts, is in general very promising for systematic studies of thermodynamic and transport properties of binary melts. In particular, it is also proved to be successful for the MD models of Ni-Al melts [20] with the EAM potential developed in [21] . Specifically, we consider 9 compositions across the binary Ni-Zr system: pure Ni, Ni 87.…”

“…Therefore, incorporating the driving force for chemical diffusion due to the difference in the chemical potential, the interdiffusion coefficient characterizes collective mass transport in a binary system under a composition gradient. In MD simulations, the Onsager coefficient for mass transport, , can be conveniently evaluated within the framework of the Green-Kubo formalism via the time integral of the autocorrelation function of the interdiffusion flux, ( ), [20,25,26,29,[30][31][32][33][34][35][36][37] as…”