Investigation On Super-plastic Micro-forming Process Of Zr-Based Bulk Metallic Glass Based On Silicon Molds

Super-plastic micro-forming process(SPMF) of Zr-based bulk metallic glass(BMG)based on silicon molds was investigated. In the first, the crystallization characteristics andsuper-plasticity in super-cooled liquid region of BMG was studied in order to determinethe main process parameters-temperature and strain rate. Subsequently, formingexperiments was conducted under appropriate process parameters, obtaining micro-gears.Finally, the atom structure, mechanical properties and dimensional accuracy of micro-partswas measured and evaluated. High-precision micro-parts verified the feasibility of SPMF,while analysis and evaluation work of the process lay a foundation for the manufacturingstandards and evaluating system. Following are research methods and results.Firstly, to get the right SPMF parameters-temperature and strain rate, theexperimental study of BMG properties was conducted. With a differential scanningcalorimeter(DSC), the onset (Tgonset) and end temperature (Tgend) of glass transition and theonset temperature of crystallization (Tx) were obtained, which determined the processtemperature region Tprocess=Tx-Tgend; crystallization incubation time under differenttemperatures and heating rates was measured by DSC, and temperature-time-transformation curve under150℃/min was depicted, which provided time constraints ofSPMF. According to the stress-strain curves, the distributions of strain rate sensitivityexponent-m and yield stress were acquired. At last, on the base of two distributions, thestrain rate range of the process was determined.Secondly, the SPMF experiments with BMG were taken out. Silicon micro-moldswere designed and fabricated using inductive coupled plasma process. An outer gear with0.05module,36teeth and a Φ0.8mm-hole was prepared at410℃and0.001s-1withuniversal testing machine. Temperature control and fixture issues of independentlydeveloped forming equipment were solved. With the equipment, the characteristics ofZr41.2was investigated, and0.03modulus66teeth inner gear was obtained.Thirdly, causes of mold breaking was analyzed, and the causes verified the three-stageof SPMF from the view of process. The oxidation behavior impact on SPMF was studiedby scanning electron microscope(SEM). As a result, the oxide layer was evenly distributed,not affecting the quality of components. The crystallization behavior impact on SPMF wasstudied by transmission electron microscopy(TEM) analysis. Nanocrystals with30-300nmdispersed in the amorphous substrate. According to four-stage crystalline phase,micro-components were either in the single multi-phase-crystal stage oricosahedral-phase stage. Using Keyence microscope and image processing software,dimensional accuracy of micro-parts were analyzed and evaluated, indicating that thecomponents had high accuracy.