Microstructural evolutions and fractal characteristics in medium range level in AlxNi100-x alloys during rapid solidification process

Abstract

Recent progress of simulations at the atomic level has led to a better understanding of the structural behaviors of metallic glasses. In this work, molecular dynamic simulations were steered to study the atomic scale structures of AlxNi100-x bulk metallic glasses. To investigate the structural evolution of a wide composition range of Al-Ni compound, we have adopted various analytical techniques: radial distribution function (RDF), coordination numbers and Voronoi Tessellation Analysis. Results of the Voronoi tessellation analysis suggested that the icosahedral-like clusters are identified as the basic local structural motifs in most compositions of Ni-Al alloys and their connection leads to the formation of medium-range order. In addition, Al-poor metallic glasses have the best glass forming ability since they are characterized by more fraction of icosahedral-like clusters. A detailed analysis of the specific Al10Ni90 shows the formation of polyicosahedra built by the intercrossed icosahedral clusters. Interestingly, the power-law scaling behavior between the coordination numbers and the coordination shell radius of AlxNi100-x indicates that the short and medium range order exhibit fractal characteristics related to the formation of icosahedral-like clusters that possesses a high atomic packing density and a low free volume.