Superplastic forging of ZrTiCuNiBe-bulk glass for shaping of microparts

Metallic bulk glasses are suitable for near net shaping of machine parts by die-forging under small loads in the low viscous state above the glass transition temperature. However, this application is limited by phase transitions in the metastable glasses, which affect the ability of superplastic moulding by degradation of the viscous properties of the material. The thermal stability and the superplastic behavior of Zr_46.8Ti_8.2Cu_7.5Ni₁₀ Be_27.5 bulk glass was investigated by differential scanning calorimetry, X-ray diffraction, microhardness measurements and by thermal mechanical analysis. From these measurements the temperature-time range was determined in which the glass can be forged without altering the microstructure significantly. At 643 K and 653 K, the glass remains sufficiently stable for 5 h and 3 h, respectively and the deformation is controlled by Newtonian flow. By pressing the glass with 5 MPa at 653 K a deformation of ε≈5 was attained. Microparts of 200 μm in width and up to 500 μm in height were moulded with excellent precision at 653 K and 653 K in a small load, high temperature vacuum press.