Molecular dynamics simulations of the melting curve of NiAl alloy under pressure

Abstract

The melting curve of B2-NiAl alloy under pressure has been investigated using molecular dynamics technique and the embedded atom method (EAM) potential. The melting temperatures were determined with two approaches, the one-phase and the two-phase methods. The first one simulates a homogeneous melting, while the second one involves a heterogeneous melting of materials. Both approaches reduce the superheating effectively and their results are close to each other at the applied pressures. By fitting the well-known Simon equation to our melting data, we yielded the melting curves for NiAl: 1783(1 + P/9.801)0.298 (one-phase approach), 1850(1 + P/12.806)0.357 (two-phase approach). The good agreement of the resulting equation of states and the zero-pressure melting point (calc., 1850 ± 25 K, exp., 1911 K) with experiment proved the correctness of these results. These melting data complemented the absence of experimental high-pressure melting of NiAl. To check the transferability of this EAM potential, we have also predicted the melting curves of pure nickel and pure aluminum. Results show the calculated melting point of Nickel agrees well with experiment at zero pressure, while the melting point of aluminum is slightly higher than experiment.

Molecular Dynamics Studies of B2 NiAl Alloy Melting Point

“…Generally, evaluating the melting point is not a straightforward approach because it requires the calculation of Gibbs free energies, which is a multistage process that needs several different molecular dynamics simulations. In case of B2 NiAl alloy many studies have conducted to find its melting point under various pressure, however the results are significant different between these research groups [1,2,4]. The discrepancies may come from different method and potential applied.…”

“…The discrepancies may come from different method and potential applied. Even in the simplest case when pressure equal zero, there are two different experiment values of B2 NiAl melting point 1911 K and 1995 K were reported from literature [2,4,8]. The authors of this work would like to provide another perspective to this classical problem in thermodynamics.…”

“…This method is empirical, which based on the classical nucleation theory [2]. In this method, there is a sudden change in volume (potential energy) when solid is heating at superheating temperature T sh far beyond the melting temperature T m , and when liquid is cooling at supercooling temperature T sc far below T m .…”

“…The volumetemperature V-T (or potential energy-temperature) curve show the hysteresis effect of heating solid and cooling liquid. The melting point T m can be estimated from T sh and T sc by the following formula [2,7,11] .…”

“…Among these structures, B2 (CsCl-type, Pm3m space group) is the most stable one both at ambient and very high pressure at room temperature [2]. The B2 NiAl compound is of particular interest from a mechanical point of view that motivate its extensive use in industry [3].…”