Molecular dynamics study of phonon-mediated thermal transport in a Ni₅₀Al₅₀melt: case analysis of the influence of the process on the kinetics of solidification

Abstract

The phonon-mediated contribution to the thermal transport properties of liquid NiAl alloy is investigated in detail over a wide temperature range. The calculations are performed in the framework of equilibrium molecular dynamics making use of the Green-Kubo formalism and one of the most reliable embedded-atom method potentials for the intermetallic alloy. The phononmediated contribution to the thermal conductivity of the liquid alloy is calculated at equilibrium as well as for the steady state. The relative magnitude of the thermal conductivity decrease induced by the transition to the steady state is estimated to be less than 2% below 2000 K and less than 1% at 3000 and 4000 K. It is also found that the phonon-mediated contribution to the thermal conductivity of the liquid alloy can be accurately estimated (well within 1%) on the basis of an approximation which invokes the straightforwardly accessible microscopic expression for the total heat flux without demanding calculations of the partial enthalpies needed for the precise evolution of the reduced heat flux (pure heat conduction). On the basis of these calculations, the correspondence between the experimentally observed and modelled kinetics of solidification due to a difference in thermal conductivity is discussed.

Thermodiffusion in liquid binary alloys computed from molecular-dynamics simulation and the Green-Kubo formalism

“…Finally, our result for the NiAl potential in Ref. [16] is in fair agreement with previous results for thermal conductivity using the same potential [17].…”

“…[17] (where it was found that, in our units, L cc = 0.035 A −1 ps −1 , L qq = 0.930 eV 2Å−1 ps −1 , and L cq = −0.020 eVÅ −1 ps −1 ) with our values obtained using the same potential, it seems that our values for L cc and L qq are in agreement, while we find a value for L cq significantly larger in magnitude than the value found in Ref. [17]. This seems to account for the difference in values for Q * c between this work and Ref [9].…”

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

“…Another conceptual approach for generation accurate and self-consistent databases of the transport and thermodynamic properties of liquid alloys can be based on molecular dynamics (MD) simulations [13][14][15][16][17][18][19][20][21][22][23]. This approach is completely free of the limitations inherent for experimental studies.…”

“…Recently, we have developed [19][20][21]23] a theoretical framework for calculation of the mass and heat transport coefficients in a binary liquid alloy via equilibrium MD simulation in conjunction with the Green-Kubo formalism using the fluxes independent of reference frame. Furthermore, we have compared our results on mass and heat transport in a Ni 50 Al 50 melt obtained with two state-of-the-art EAM potentials [26,27] developed for the alloy.…”

“…Since the thermodynamic factor is dimensionless quantity, has units of a diffusion coefficient. Meanwhile, the convenience of the use of to characterize * ' the thermotransport process is related to the fact that, in an isothermal (without any temperature gradient) binary melt, represents the reduced heat flow (pure heat * ' conduction) consequent upon unit interdiffusion flux [19][20][21], so that . Since, both ' = * ' and are invariant to change of reference frame, the reduced heat of transport is…”