Plastic Deformation Behavior Of Zr-based Bulk Metallic Glasses In The Supercooled Liquid Region And Finite Element Simulation

In this dissertation, the structure, thermal stability, plastic deformation behavior, the influence of plastic deformation on structure and properties of Zr55Cu30Al10Ni5 bulk metallic glass have been systematically investigated by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC), Zwick/Roell mechnial testing system and HV-1000 micro-Vickers sclerometer. Uniaxial compressive tests of Zr55Cu30Al10Ni5 BMG in the supercooled liquid region are simulated by finite element method (FEM).Zr55Cu30Al10Ni5 bulk metallic glass (BMG) has been prepared by copper mold casting. The results of DSC indicate that Zr55Cu30Al10Ni5 BMG exhibits a wide supercooled liquid region. Based on the TTT curve of Zr55Cu30Al10Ni5 BMG, a series of forming temperatures and strain rates is selected for uniaxial compressive tests in the supercooled liquid region.Plastic deformation behaviors of Zr55Cu30Al10Ni5 BMG are studied by Zwick/Roell mechnial testing system in the supercooled liquid region (417℃~452℃) under different strain rates ranging from 5×10-4s-1 to 1×10-1s-1. It has been found that both temperature and strain rate significantly affect the plastic deformation behaviors. Zr55Cu30Al10Ni5 BMG exhibits Newtonian behavior at low strain rates, but beomes non-Newtonian behavior at high strain rates. Thus the best deformation region in the supercooled liquid region can be supported(437±5℃,1×10-3s-1 ~1×10-2s-1). The influence of plastic deformation behavior on the structure, thermal stability and micro-vickers hardness has been systematically investigated by XRD, DSC and micro-Vickers sclerometer. It has been found that samples after deformation basically keep the amorphous structure without diffraction peaks detected, but for deformed samplesΔH decreases and micro-Vickers hardness increases.Three different equations have been used for expressing the relation of flow stress, strain rate and temperature. The temperature dependences of viscosity in supercooled liquid region can be fitted well with the Vogel-Fulcher-Tammann (VFT) equation. It has been shown that Zr55Cu30Al10Ni5 BMG is a strong liquid with the nature of high glass forming ability (GFA). Based on superplastic rheological constutive equation which is suitable for Newnoian liquid region, fitting parameters are systematically calculated at 427℃, 437℃and 447℃. Extended exponential function establishes the relation of flow stress, strain rate and temperatures. Such relation describes Newtonian behavior transferring to non-Nowtonian behavior with decreasing temperature and increasing strain rate.The finite element simulations of uniaxial compressive tests were carried out using superplastic rheological constutive equation based on DEFORM-3D software. Simulation results fit well with experimential results in Newtonian liquid region, but the agreement between simulation and experiment is poor in non-Newtonian liquid region. The simulation results for plastic deformation exhibits that both temperature and strain rate significantly affect the plastic deformation behaviors. The trendency agree with experimential results very well.