Simulation Study Of Plastic Deformation And Surface Friction Behavior Of CuZr-based Amorphous Composites

The extremely poor room temperature plasticity of amorphous alloys limits their wide application,mainly due to the formation of a single local shear zone caused by the strain localization in the amorphous matrix when the amorphous alloy is mechanically loaded,which triggers catastrophic failure.To solve this challenge,the plasticity of crystalline/amorphous composites can be improved by preparing them.In this thesis,the amorphous/B2-Cu Zr nanocrystalline composites of Cu-Zr system are designed by molecular dynamics simulations,which include the study of the effects of these factors,such as the size and distribution of nanocrystals and the crystal orientation,on the plastic deformation behavior of the composites,the effect of the introduction of alloying elements in the Cu-Zr system on the structure and its correlation with plasticity,and the effect of alloying elements and nanocrystals on the plastic deformation of the composites In order to explore the amorphous matrix composites with high performance and suitable for complex applications,the surface friction behavior of the composites formed by adding alloying elements or both alloying elements and nanocrystals to the Cu-Zr system is also investigated in this thesis.The main research contents of this thesis are described below.（1）When studying the effect of B2-Cu Zr nanocrystal size on the plasticity of the composites,it was found that the larger the size,the higher the elastic modulus of the nanocrystal/amorphous composites,and the nanocrystal/amorphous composites with a size of 1.9 nm had much higher comprehensive mechanical properties than the other sized samples at strains less than 15%,with yield stresses close to 3 GPa and yield strains as high as 7.5%.Finally,by studying the variation of LS atomic ratio with strain,it was found that changing the nanocrystal size can modulate the plastic deformability of amorphous matrix composites and change the value-added extension behavior of the shear zone.In the study of the effect of nanocrystal distribution and crystal orientation on the plasticity of the composites,it was found that the samples were more likely to obtain multiple shear bands distributed in the amorphous matrix when the samples were distributed in AB,[110] crystal orientation and the nanocrystals were farther apart,resulting in a greater increase in plasticity and strength of the amorphous matrix composites.（2）For the study of the structure of Cu-Zr-Ag system,it is found that the bonding of Zr-Ag atomic pairs is the strongest among all atomic pairs,and the tensile simulation of the amorphous Cu-Zr-Ag system reveals that the plasticity of the samples with Ag content of 20at% is better,and the yield stress is more than 2.5 GPa,and the proportion of <0,0,12,0>polyhedra is not damaged a lot during the tensile process This indicates that the plastic deformation is very uniform.Moreover,the addition of Ag improves the yield strength and elastic modulus of the amorphous Cu-Zr-Ag system,thus the tensile plastic deformation behavior of the amorphous composites containing both Ag and B2-Cu Zr phases is also investigated in this thesis,and it is found that the joint action between Ag and B2-Cu Zr phases enhances the plastic gain effect of the pure amorphous matrix significantly.（3）Starting from the design of high-performance amorphous matrix composites,the surface friction behaviors of amorphous alloy composites in the Cu-Zr-Ag system and B2-Cu Zr nanocrystal/Cu-Zr-Ag system were simulated using molecular dynamics in this paper.The results showed that: the friction force increased with the increase of friction depth,and the friction force could reach 60 e V/（?） at the friction depth of 3.6 nm;the surface friction behavior was not changed by the change of Ag content;the friction coefficient of the Cu-Zr-Ag system amorphous alloy increased with the increase of friction speed,and the friction coefficient was close to 0.9 at the friction speed of 120 m/s;the friction force increased with the increase of temperature decreases with the increase of temperature;the size of both spherical and conical grinding heads is 2 nm,and the wear mechanism of both changes from abrasive wear to adhesive wear,and the corresponding wear amount of spherical grinding head is much larger than the wear amount produced by conical grinding head on the composite material,and there is a great difference in the surface friction behavior between the two.The study of plastic deformation behavior and surface friction behavior of amorphous matrix composites can analyze and grasp the plastic deformation behavior and shear band extension mechanism of amorphous alloys under tensile stress from the atomic scale,thus providing important theoretical support for the development of new amorphous matrix composites.