Study of Size Effect on Ni60Nb40 Amorphous Particles and Thin Films by Molecular Dynamic Simulations

Ni60Nb40 amorphous particles (APs) and amorphous thin films (ATFs) with various sizes were investigated by molecular dynamic simulations. It is revealed that sample size has effects on both Ni60Nb40 APs and ATFs composed of shell or surface and core components. Ni60Nb40 APs have an average bond length of 2.57 & Aring; with major fivefold-symmetry atomic packing and low bond-orientation orders of Q(6) and Q(4) in both core and shell components. Ni atoms in Ni60Nb40 APs and ATFs prefer to segregate to the shell and surface regions, respectively. Atomic packing structure differences between various-sized Ni60Nb40 APs and ATFs affect their glass transition temperatures T-g, i.e., T-g decreases as the particle size or the film thickness decreases in Ni60Nb40 APs and ATFs, respectively. Our obtained results for Ni60Nb40 APs and ATFs clearly reveal a size effect on atomic packing and glass transition temperature in low-dimensional metallic glass systems.