A study of the nanoindentation creep behavior of (La0.5Ce0.5)65Al10Co25 metallic glass based on fractional differential rheological model

A fractional differential rheological model was proposed to describe the nanoindentation creep behavior of metallic glasses (MGs) at room temperature. The model had been proved to not only include the conventional rheological model, but can be used to obtain the empirical formula that has been commonly used to characterize nanoindentation creep behavior of MGs. The reversible and irreversible parts of time-dependent deformations of (La0.5Ce0.5)65Al10Co25 metallic glass were obtained through nanoindentation creep experiments, and the results were used to investigate the effects of the creep load Pmax and the loading rate Ṗ on the creep behavior and the variations of the model parameters. The results indicate that the fractional differential rheological model can describe the creep deformation quite well. Parameters analysis shows that viscoelastic part of creep and β relaxation has many common points. The variation of irreversible viscoplastic part of creep with creep load is the main cause of indentation size effect. The load rate Ṗ has effect on all components of creep deformation, which is reflected by the variations of the rheological model parameters. The viscosity and retardation time are related to the loading history as indicators that characterize the system's instantaneous viscosity at the onset of creep. The fractional order and creep stress exponent varies with loading rate have similar pattern, which could reflect the flowing ability upon the completion of the creep experiment.