Vibration Plastic Forming Mechanism And Finite Element Analysis Of Zr-based Bulk Metallic Glass

Bulk metallic glasses (BMGs) exhibit superplasticity in the supercooled liquidregion, therefore BMGs can be used to fabricate micro-nanoscle structures/devicesapplied in modern industry, through hot-embossing in a low-cost, high-efficiency andrapid prototyping style. However, the “size effect” brought by the miniaturization is oneof the core issues in the micro-forming field. With decreasing forming size, theinterfacial friction between BMGs and surfaces of mold cavity gradually becomes themain factor that affects the formability. Currently, methods by raising temperature andextending processing time to improve formability of BMGs, but these methods caninduce the possible crystallization, which limit the batch manufaction and industrialapplication. Vibration plastic forming is a commonly method to improve the formingability of traditional metals and polymers, due to its effectiveness in reducing formingstress and interfacial friction. The introduction of vibration loading to the micro/nanoforming of BMGs will improve the micro/nano formability, effectively. However, therelated research is rare and the mechanism is unclear.The vibration loading method was used to systematically study the effect of loadingfrequency on thermoplastic formability of BMGs in the supercooled liquid region.Through theoretical analysis, the changes of flow unit and free volume with temperatureunder different loading frequencies were calculated. The constitutive equations with freevolume parameters were established, and finite element analysis was carried out. Thevariation of free volume with loading frequency for the BMG under vibration loading inthe supercooled liquid region was studied in-depth, which revealed the physicalmechanism of vibration-enhanced thermoplastic formability of BMGs.Firstly, the constitutive equation with free volume parameter was constructed based onfree volume theory. The simulation was carried out through commercial Deform software, the distribution of free volume thermoplastic deformed BMG sample was obtained withthe help of commercial Tecplot software. The validity of the constitutive equation wasverified by comparison of stress-stain curves between simulated and experimental results.Secondly, the Dynamic Mechanical Analyzer (DMA) was used to tense the Zr-basedBMG with vibration loading condition, in order to reveal the effect of vibration loadingfrequency on thermoplastic formability (evaluated by the plastic strain) of BMGs. Thecomplex elastic moduli of the samples under various loading frequencies were measuredby the single cantilever bending method. The variation of flow unit and free volumeunder different loading frequencies with temperature were calculated theoretically. Theconstitutive equations with free volume parameters were applied and the distribution offree volume in thermoplastic deformed sample was obtained. On the basis of aboveresearch, we prposed that the varibation-induced softening and homogeneous flowing arethe main reasons that fascilite the thermoplastic formability of BMGs.Finally, we further studied the influence law of vibration loading on formability ofamorphous alloy in microscale mold. Through hot-pressing experiment, the microstamping columnar array were hot-imprinted under two different frequencies, andcompared with the hold loading condition. The influence rule of the vibration loading onthermoplastic formability of BMGs in microscale mold, which further verify theeffectiveness of the vibration-enhanced formability.