The Deformation Of Vit1Bulk Metallic Glass Under High Pressure Torsion

With excellent mechanical, physical and chemical properties, metallic glasses have awide range of applications and are of great scientific interest. The aim of this work is tostudy the microstructure of Zr41Ti14Cu12.5Ni10Be22.5bulk amorphous alloy before and afterhigh pressure torsion by using X-ray diffraction (XRD), differential scanning calorimetryinstrument (DSC), scanning electron microscopy (SEM) and transmission electronmicroscopy (TEM).And considering the characteristics of unconstrained high pressuretorsion, we modeled and simulated the deformation process within finite element methodimplemented in DEFORM-3D software, analyzing the deformation and temperaturedistribution after high pressure torsion, to compensate for the insufficient of experiment.The Vit1metallic glass samples，with a height to diameter ratio1:10, showed a goodplastic deformation in the high pressure torsion test: the deformation of central region canreach80%. It turns out that the pressure, the number of twist turns and friction factor allhave direct effects on the heat generating and deformation of the sample. A thermocouplewas embedded in the sample to measure the temperature changes of the sample in theprocess of high pressure torsion. By measuring the change of hardness and density of thespecimen before and after the high pressure torsion，it was found that the hardnesssignificantly decreased and the density increased slightly. The influence of thedeformation on the structure of the metallic glass samples by high pressure torsion wasanalyzed. Compared with the compression test, the amorphous alloys showed plasticdeformation after high pressure torsion. The XRD analysis results of the samples beforeand after high pressure torsion showed that there is no crystallization occured in thesample, and it excluded the possibility of high pressure torsion induced nanocrystallization.After high pressure torsion, the sample’s supercooled liquid region increased and thermalstability improved indicated by the DSC analysis. SEM analysis found that the fracturesurface becomes rougher and rougher from the outermost layer to the innermost layer, andthat high pressure torsion induced a large number of shear zone, resulting in plasticdeformation of the amorphous alloy. The microstructural characteristics of the sample areanalyzed by TEM and it shows that after the high pressure torsion, the structure remains indisordered state. Wrapping the outside of the metallic glass sample, of which the height todiameter ratio is1:5, the fracture becomes not obvious. Finite element simulation results show that, the deformation of the sample agreeswell with the experimental results, and the temperature changes increase continuouslyduring the process, up to125°C, far below the glass transition point.