Study On The Plastic Deformation Of Mg-based Bulk Metallic Glass

In this paper, Mg₆₅Cu₂₅Y₁₀bulk metallic glasses prepared by copper mould casting were employed to perform compression tests both in the supercooled liquid region and below glass transition temperature(T_g). The effect of holding temperature, loading stress and loading time on deformation behavior of Mg-based bulk metallic glass have been studied and relationships between flow stress, strain-rate, viscosity and temperature have also been analyzed. It is proposed that plastic deformation behavior exists both in the supercooled liquid region and below T_g. The deformation degree depends on holding temperature, loading stress and loading time. In the supercooled liquid region, plastic deformation requires certain holding temperature, loading stress and loading time. Crystallization process undergoes more quickly at higher temperature, under larger stress, or for longer time. At temperatures below and near to T_g, a longer holding time is required to attain considerable deformation degree. Under low loading, the flow-stress has a linear dependence on strain-rate and the plastic deformation exhibits Newtonian viscosity behavior in the supercooled liquid region.Plastic formation of the Mg-based bulk metallic glass was performed in thesupercooled region. The forming properties have been studied by using opticalmicroscope(OM), X-ray diffractometer(XRD), scanning electron microscope(SEM) and atomic forced microscope(AFM). The stress-induced crystallization and the effect of crystallization on plastic deformation have also been discussed. It is shown that Mg-based bulk metallic glass has almost precisely replicated the mould surface in the supercooled liquid region, which provides a potential approach for preparing micro-devices. Based on the microstructure of samples under different conditions, Mg-based bulk metallic glass is believed to be easier to crystallize under loading. Crystallization leads to the deformation incompatibilities between the metallic glass matrix and the crystals due to the "pinning" effect of crystals. With the time evolution, the equilibrium state changes and the glass viscosity increases gradually.This paper also presents the tensile deformation behavior of the Mg-based metallic glass ribbon with the same composition in the supercooled liquid region. As a comparison, we have also performed tensile test at room temperature. The fracture mechanism has been briefly discussed. In the supercooled liquid region, Mg-basedmetallic glass ribbon has a homogeneous rheological deformation under low stress, accompanied by a maximum tensile elongation up to 100%. A partial contraction occurs during fracture because of cavities diffusion and connection due to kinetic instability during tensile deformation. The metallic glass ribbon has high fracture strength and brittle fracture occurs during loading at room temperature. However, local plastic fracture has been found in some shear bands.