Analysis of icosahedral structure in rapidly solidified Pd₈₂Si₁₈ amorphous alloy under high pressure

Abstract

Compared with traditional glass, metallic glass (MG) has excellent properties, such as high strength, high hardness, high fracture toughness, good soft magnetic properties and corrosion resistance due to its unique structure. Such properties enable it to be used in optics, electronics, construction and other fields, making it a highly promising new material with great application potential. As the properties of amorphous alloys are closely linked with their local structures, microstructure characteristics have always been a research focus in the amorphous field. Previous studies show that the onset temperature of heredity and hereditary fraction of characteristic clusters can be used to effectively evaluate the ability of an amorphous alloy to form glass. In order to obtain the relationship between the microstructure characteristic and cluster evolution of amorphous alloy, and reveal the formation of glass, the glass transition processes of the Pd₈₂Si₁₈ alloy under different pressure conditions are simulated by using the molecular dynamics method, and the heredity and evolution of the Pd₈₂Si₁₈ amorphous alloy are analyzed by using the cluster-type index method and the reverse tracking method. The simulation results show that the glass transition temperature of the Pd₈₂Si₁₈ alloy can be increased when the pressure is higher, and a large number of icosahedra are formed in the solidified alloy when the pressure is sufficiently high. Icosahedron is a kind of structure that widely exists in amorphous materials and has been studied for quite a long time. In this work, a detailed comparative analysis on two icosahedra is conducted and the heritability of clusters with different chemical compositions under high pressure is studied. The results show that it is easier for icosahedra with central atom Pd and those with central atom Si to form a medium-range order in the Pd₈₂Si₁₈ amorphous alloy. An increase in pressure conduces to the increasing of both onset temperature of heredity and hereditary fraction. Comparing with the results of cluster heredity analysis under 0 GPa, the Si-centered clusters have stronger heritability than Pd-centered clusters, thus the former ones have a greater influence on the ability to form glass. These findings are of significance in understanding the relationship between microstructure evolution and glass formation,and also providing certain guidance for designing amorphous alloys.