Superplastic nanoforming of Zr-based metallic glass at high strain rate under rapid heating

摘要

The glass transition and crystallization phenomena were studied on ZrAlCuNi bulk metallic glass under rapid heating.Cylindrical specimens of 2 mm in diameter were heated by induction heating at a rate of up to 200 Ks-1.During the heating,glass transition temperature Tg and the crystallization temperature Tx increase with increasing heating rate.Furthermore,the temperature range of the supercooled liquid state ΔTx becomes wider.In addition,deformation behavior during heating was studied under a compressive load.The material exhibits a Newtonian viscous flow in the temperature range of the supercooled liquid state,and the normal viscosity decreases with increasing heating rate.The normal viscosity is 5x104 Pas at a heating rate of 100 Ks-1.As an application of this phenomenon,characteristic nanoforming should be performed at very high strain rates during rapid heating and realize a highly effective processing in a short time.In the present study,we developed a new nanoforming system.The system consists of a rapid heating unit by resistance heating,a unit of detecting the glass transition phenomenon by measuring the stress relaxation phenomenon due to glass transition of pre-strained specimen and an electromagnetic linear actuator for driving a micro-forming tool and their control circuit.Characteristic forming behavior depends on specimen and tools temperatures during rapid heating,because the thermal capacity of the specimen is so small.FEM simulation was carried out on heat transfer among specimen and tools during the forming.With these apparatus,specimen was heated at a rate of 103Ks-1 and diffraction grating was successfully formed on the surface of the specimen within 0.5 seconds.The nanoforming system for metallic glasses is effective for mass production of micro parts for MEMS.