Research On Mechanical Properties Of Metallic Glasses And Their Composites At Atomic Scale

Metallic glass is an amorphous alloy formed by cooling the high-temperature alloy melt rapidly.Due to its disordered atomic arrangement,metallic glass does not have some crystal defects,e.g.,dislocations and grain boundaries,resulting in high strength,high hardness and high elastic limit.These excellent mechanical properties make metallic glass bear the potential for applications involving armor protection.The relevant research on shock response is conducive to a better understanding of its dynamic mechanical properties and failure process,and to broaden its application range.In addition,the highly localized shear deformation dominated by a few shear bands often occurs in the metallic glass upon loading,which demonstrates the characteristics of macroscopic brittle failure.In order to deal with this fatal flaw,material scientists introduce a second,crystalline phase to form the metallic glass/crystalline phase composite and thus achieve the toughening of the material.Investigating the strengthening and toughening mechanism of metallic glass composites has important theoretical guidance significance for the design of innovative metallic glass composites.Furthermore,the explanation of the mechanism at the atomic scale is the key to understanding the issues mentioned above.Given the lack of effective in-situ real-time detection techniques,molecular dynamics simulation has become a powerful tool for these studies.The specific research details are as follows:（1）Using molecular dynamics simulations and X-ray diffraction simulations,the high-speed shock compression process of metallic glass is analyzed and the evolutions of short-and medium-range orders characterized by icosahedra and icosahedron networks are traced.In addition,the corresponding X-rays diffraction information is acquired and provides guidance for the interpretation of the experimental diffraction information upon shock loading.At molecular dynamics scales,crystallization is not observed during the shock compression process.Upon a weak shock loading with the strength below 60 GPa,shock compression causes the increase（or the growth）of icosahedra and their networks,which is reversible upon release.On the contrary,the strong shock（above 60 GPa）leads to shock melting and thus the irreversible destruction of the icosahedra and their networks.（2）Molecular dynamics method is utilized to simulate the plastic deformations of Cu₆₄Zr₃₆metallic glass/crystalline Cu bicontinuous phase nanocomposites,Cu₆₄Zr₃₆ nanoglass/nanocrystal Cu composites and amorphous/crystalline nanolaminates under uniaxial tension or nanoindentation.The simulations on Cu₆₄Zr₃₆ metallic glass/crystalline Cu bicontinuous phase nanocomposites demonstrate that the increase in the specific interface area can significantly promote the growth of shear transformation zone and the enhancement of the tensile ductility.Additionally,the introduction of grain boundaries to the crystalline phase can effectively improve the uniform deformation of metallic glass composites and mitigate strain localization.The simulations on Cu₆₄Zr₃₆ nano glass/nanocrystalline Cu composites systematacially compare the effects of grain boundaries,glass-glass interfaces,and glass-crystal interfaces on plastic deformation.By selecting the appropriate proportions of various interfaces,the comprehensive control of hardness,strength and toughness can be realized.At last,the study on amorphous/crystalline nanolaminates has shown that reducing layer thickness and introducing grain boundaries and glass-glass interfaces into nannolaminates are two main methods to improve their ductility,which can facilitate the transition from inhomogeneous deformation to co-deformation.