Bulk Amorphous Alloy Nanoindentation Behavior And Its Numerical Simulation

Because of their superior physical properties such as ultra-high strength,high elastic limit and a high hardness,amorphous alloys have attracted researchers' attention.Amorphous alloys' unique atomic structure results in their special properties,for example,their structures are long range disordered in a liquid-like manner.The structure of amorphous alloys has been a long-standing mystery,and investigation on the relation between the atomic-level structure of these alloys and its mechanical behavior has aroused much interest in the materials science and condensed matter physics.In this paper,main research content includes the following three parts:?1?intermittent plastic flow of an Pd-based bulk amorphous alloy?BAA?under nanoindentation;?2?the microstructure evolution of amorphous alloys during nanoindentation creep;and?3?nanoindentation creep behavior in bulk amorphous alloys and its simulation using finite element analysis.The main results are as follows:1.The speed signal of the serrated flow is separated from the displacement speed signal during loading stage by eliminating the interference.Then the serrated flow of amorphous alloy under different loading rates is systematically analyzed based on the separation signal.It is found out that with the increase of loading rate,the number of serrated flow occurred during indentation,the total displacement and the average duration of serrated flow all show a trend of decrease,except the average speed of serrated flow.2.Based on the collaborative shear model,the STZ volume of Pd₄₀Cu₃₀Ni₁₀P₂₀ amorphous alloy is calculated.Then the relationship between the volume and loading rate and the maximumload is analyzed.Finally,a reasonable explanation is given consulting the experiment curve of serrated flow.3.Combined the microstructure evolution of the amorphous alloy under different loading condition with fractional order differential theory,the relationship between indentation creep displacement and time expessed by fractional order differential is established.Based on the derived formula,the nanoindentation creep displacement-time curve of Pd-based bulk amorphous alloys(Pd₄₀Cu₃₀Ni₁₀P₂₀)under different loading rate and the maximum load of are nonlinearly fitted.It is cocluded that the creep behavior of amorphous alloy has significant loading condition sensitivity.4.The rheological microunit evolution under different loading condition is analyzed systematically according to the fitted parameters.Meanwhile the rheological unit evolution law of amorphous alloy with three kind different plastic deformation ability is compared.It is founded that the plastic deformation ability of amorphous alloy has a close correlation with their internal viscoelastic rheological unit.5.According to the comparison between the indentation creep experiment data and finite element analysis,there is a conclusion that Drucke-Prager?D-P?criterion can describe the plastic behavior of Zr₄₈Cu₃₂Ni₄Al₈Ag₈ amorphous alloy more accurately.The equivalent stress,strain,and the pile-up distribution around the tip can be derived by the simulation of the experiment process via Abaqus software.