Impact of three-body interactions in a ReaxFF force field for Ni and Cr transition metals and their alloys on the prediction of thermal and mechanical properties
YK Shin and YW Gao and D Shin and ACT van Duin, COMPUTATIONAL MATERIALS SCIENCE, 197, 110602 (2021).
In this work, we discuss the temperature-dependent elastic constants, thermal expansion and melting temperature of Ni and Cr transition metals using a ReaxFF reactive force field. While the ReaxFF force field has been successfully applied to various chemistries on these transition metals, it cannot replicate the experimentally observed relationship between C12 and C44. In addition, ReaxFF predicts the negative stacking- fault energy for fcc Ni, accelerating the fcc -> hcp phase transformation. We show that by introducing three-body interaction parameters to the metal force field, which have not been included previously for transition metals, ReaxFF can successfully predict experimental elastic constants of fcc Ni and bcc Cr at finite temperatures. We then evaluate the thermal lattice expansion at T = 0 - 1700 K and compare to experimental data available in the literature - the higher thermal expansion coefficient corresponds to Ni, which is known to have a lower melting temperature than Cr. To estimate the melting temperature of Ni and Cr using the ReaxFF force field, we performed molecular dynamics (MD) simulations by adopting the hysteresis method. With a sufficiently large system size and void concentration, the melting temperature is predicted to be 1698 K for Ni (agreeing within 1.7%) and 2410 K for Cr (within 10%). Furthermore, we develop a Ni/Cr alloy force field by combining Ni and Cr force fields and optimizing their cross-interaction parameters. It is shown in both ReaxFF and DFT that fcc-based Ni3Cr is the most stable phase with a negative heat of formation while all bcc alloys have positive heats of formation, indicating a possible phase separation for Ni and Cr. The elastic constants at 0 K calculated by ReaxFF agree with DFT values within 5-10%, except for the large deviation in C33.
Return to Publications page