Structure and thermal expansion of coordination shells in solid and liquid Invar alloys by molecular dynamics study

Abstract

Classical molecular dynamics simulations have been performed to study the atomic structures and thermal expansion of coordination shells in solid and liquid Invar alloys. Analysis of atomic structures reveals that there is an attraction between Fe-Ni nearest pairs, and that structural order still exists in the liquid Invar alloy. Fe—Ni bonds are found to have the smallest thermal expansion in the solid Invar alloy among three types of bonds, which plays an important role in the Invar effect. We also discover that the thermal expansion coefficient will gradually get close to the macroscopic level as the coordination shell number increases in Invar alloys. It is until the 5th coordination shell in the solid state and the 4th coordination shell in the liquid state that the thermal expansions of the coordination shells can reach the macroscale value. This study further promotes the understanding of the thermal expansions from the atomic scale.