Study On Constitutive Equation Of Zr-based Bulk Metallic Glasses Based On Size Effect

As the bulk metallic glass have excellent mechanical properties, which thesuperplastic in supercooled liquid region is very suitable for microforming, and thespecimen size effect will greatly impact upon microforming, so it is determined to studythe specimen size effect of bulk metallic glass, and to get constitutive relation based onsize effect. So we select Zr₅₅Cu₃₀Al₁₀Ni₅, and study the size effect in its supercooled liquidregion, establishing the constitutive equations and the fitting, finally use finite elementmethod for validation.Copper casting mold was used to prepare the Zr₅₅Cu₃₀Al₁₀Ni₅bulk metallic glass indiameter of3mm，2mm，1mm，0.6mm. And use X-ray diffraction analysis （XRD） anddifferential scanning calorimeter （DSC） of samples obtained for structural analysis andthermal analysis, to obtain their composition and thermal performance parameters （such asglass transition temperature Tg, crystallization temperature Tx, the supercooled region ΔT）.Based on the performance of Zr₅₅Cu₃₀Al₁₀Ni₅bulk metallic glass, a experimentalprogram was developed. Zwick/Roell machinial testing system was used to study the sizeeffect with different strain rate, different temperatures, different sizes of high-temperaturecompression tests, and stress-strain curves obtained for analysis. The experimental resultsshow that in the supercooled liquid region, mechanical properties of bulk metallic glassshow significant size effect, and summarize the regularity.In order to study the size effect of bulk metallic glass in supercooled liquid region, inthis paper, based on the Maxwell-Pulse constitutive model, we add the size factors S_σf,S_σos,S_εosto characterize the size effect. Contrast the data and curves of experimentsand fitting, both of the true stress-strain curves fit very well.Use the finite element simulation software to verify the proposed constitutiveequation based on Deform-3D software. Simulation results show that the improvedMaxwell-Pulse constitutive model can fit the size effect of Zr₅₅Cu₃₀Al₁₀Ni₅bulk metallicglass in the supercooled liquid region very well. Not only fitting the changes ofsteady-state flow stress, but also the changes of stress overshoot phenomenon.