Evolution Of Atomic Structure During Deformation Of Phase Separated Cu-Zr-Ag Amorphous Alloys

Metallic glasses(MGs)have many excellent properties,but the poor glass-forming ability(GFA)and low room temperature plasticity limit the application of MGs as structural materials.Nano-scale phase-separated glass can effectively improve its room temperature plasticity,but the mechanism of plastic deformation needs to be further explored.Taking the Cu-Zr-Ag alloy as an example,we use molecular dynamics simulation to investigate the structural and dynamic characteristic of the alloy system by adjusting element content.The structural evolution of the alloy system during deformation was investigated by room temperature compression and dynamic mechanical experiments.By comparing the liquid and amorphous structure of(CuZr)100-xAgx(x=0,10,20,33)alloy,it is found that Ag-Ag atom pairs aggregate more obviously in amorphous state,and there is obvious chemical inhomogeneity in MGs.With the increase of Ag content,the dynamics of melt alloy becomes faster.The dynamic heterogeneity decreases,but the stronger chemical inhomogeneity promotes the partition of fast dynamic regions and slow dynamic regions,reduces the cooperation between fast dynamic regions and slow dynamic regions,leading the GFA improvement.Compression experiments on amorphous samples,the amorphous alloys exhibit lower elastic limit.lower yield strength and lower AT with the increase of Ag content,indicating that the samples have a lower strain localization trend.Further study shows that the distribution of local shear strain is more uniform with the increase of Ag.With Ag content increasing,the difference between the number of full icosahedron<0.0,12,0>(FI)before and after deformation increases,and the W value decreases more during deformation,indicating that plastic deformation occurs in more regions of the system.With the increase of Ag content,icosahedral content increases,and the degree of interconnection is enhanced,the Ag-centered FI is more unstable than Cu-centered FI.the network structure formed by Ag-centered FI is unstable during deformation,and is easier to be disrupted.In(CuAg)100-xZrx(x=0,10,20,33.4)series MGs,as Zr contents increasing,the degree of phase separation decreases gradually.The addition of Zr atoms slows down the dynamics and enhances the dynamic heterogeneity.Compression experiments on amorphous samples show that with the increase of Zr content,the samples exhibit higher elastic limit and higher yield limit.The plasticity of the samples decreased slightly,but good comprehensive mechanical properties were obtained.Local strain mainly distributes in Ag-rich region,so the distribution and size of Ag-rich region have great influence on the distribution of local shear strain in deformation process.With the increase of Zr content,the degree of phase separation of samples decreases,the Ag-rich region decreases uniformly and distributes in samplesand the local shear distribution of the samples becomes more homogeneous.Structurally,with Zr content increasing,the difference of FI before and after deformation is smaller and the W value decreases less,incidating the FI become more stable.The network structure formed by Ag-centered FI becomes more stable during deformation and is not easy to be destroyed during deformation.The effect of temperature and mechanical strain on the relaxation dynamics of the system is similar by DMA simulation of Cu45Ag45Zr10.As temperature increasing,the sample happens a relaxation at 600K.The fraction of<0,0,12,0>of fast atoms decreases significantly and the fraction of<0,3,6,4>,<0,4,4>,<0,2,8,3>,<0,2,8,4>increased.Atoms in fast atomic region are more likely to form lower five-flod symmetry structure,which leads to structural instability.By changing the amplitude,the sample begins to relax at the amplitude of 6%.