Research On Deformation Behavior Of Ti-based Bulk Metallic Glass Composite

Bulk metallic glass composite(BMGC)exhibits better mechanical properties than bulk metallic glass(BMG)due to their double phases microstructure.Ti-based BMGC has been widely concerned for their characteristics of low density,high specific strength and relatively low modulus.Previous investigations on BMGCs are mostly focused on the improvement of preparation method,development of new alloy composition and the adjustment of microstructure worked on the macro mechanical properties.However,the microstructural evolution during deformation,the rheological behavior in the supercooled liquid region and dendrite softening region are still barely investigated.Accordingly,the investigation in this study focus on the self-designed Ti-based BMGC systematically by adopting the research approaches of experiment,theoretical analysis and numerical calculation,including these aspects: the states of the BMGC at different temperatures and the microstructural evolutions during these deformation processes.The main contents and conclusions are listed below:1.The dynamical mechanical properties of the BMGC has been studied by dynamical mechanical analysis.As a result,there are three distinct temperature regions: the elastic state,the viscoelastic state,and the elasticity raising state.The relationship between the correlation parameter and temperature is a conic curve,and the experimental data can be fitted by this relationship well,this behavior can be well described by the QPD model.2.The deformation behavior of Ti50Zr20Nb12Cu5Be13 BMGC at ambient temperature was investigated systematically by uniaxial compressive and tensile tests.The BMGC has very excellent mechanical properties at ambient temperature.In this condition,the shear bands generated in the matrix were impeded and absorbed by the dendrite,so more plasticity shear bands can be generated in the matrix to improve the plasticity of whole composite.The compressive fracture surface contains two regions: vein shape area and step shape area.The tensile fracture is full of dimples.3.The rheological behaviors of two BMGs and Ti50Zr20Nb12Cu5Be13 BMGC in the supercooled liquid region were investigated by uniaxial compressive and tensile tests systematically.By calculating the activation volume and the migration of atomic cluster,indicating that the BMGs have the better rhelogical property than the BMGC.By calculating the strain rate sensitivity exponents,the sensitive to the strain of the BMGC was studied.The dendrite morphology was not changed after tests,the rheological behavior of the composite is governed by the super-plastic matrix,the dendrite can only transfer the applied stress.The tensile fracture surface was also full of dimples,but it's different with the dimples at ambient temperature.4.The deformation behavior in the dendrite softening region of the Ti50Zr20Nb12Cu5Be13 BMGC has been investigated by uniaxial compressive and tensile tests in detail.The result indicates that the crystallization fraction of the glassy matrix has much effect on the mechanical properties under compressive test,but not the tensile test.The strain rate sensitivity exponents in tensile test is much larger than that in compressive test.The dendrite morphology changes a lot after deformation,the rose-like dendrite changes into spherocrystal firstly,and then the spherocrystal undergoes severe plastic deformation.In this condition,the crystallized matrix can only transfer the applied stress,and the softened dendrite absorbed all the applied stress to perform plastic deformation.