Simulation And Experimental Verification Of Heterogeneous Plastic Deformation Of Disks In The Process Of High Pressure Torsion

As one of effective processes in many severe plastic deformation (SPD) processes, high pressure torsion (HPT) can effectively prepare ultra-fine grained (UFG) material.Ultrafine-grained materials have excellent mechanical properties and processing performance due to their special surface structure and grain structure, and have attracted the attention of scholars from all over the world.Although the experiment of the process parameters on the plastic deformation during the high-pressure torsion process is very intuitive and effective, the various field information such as the temperature field, the stress strain field are not easy to obtain. In addition, the inhomogeneous deformation of HPT processed disks has not been paid enough attention. This has become one of the problems on fabricating of ultra-fine grained material and process optimization of high pressure torsion.In this study, properties and affecting factors on inhomogeneous plastic deformation process of different materials were investigated during HPT process by FEM analysis(ANSYS and DEFORM-3D software) and physical experiment.The main results and conclusions are listed as follows:(1) The effects of pressure and revolution on the plastic deformation in the compression stage and torsion stage respectively were investigated. The results indicates that the degree of inhomogeneous distributions of effective strain, hardness and microstructure of HPT disks is increased with the increase of the pressure and the number of torsion respectively. There is a same distribution trend with lower strain and hardness, coarse grains in center and higher strain and hardness, refined grains in edge along the radial direction of HPT processed disks.Moreover, three zones of hardness hill, dead metal zone (DMZ) and soften region are not consistent with the overall deformation trend. In addition, severe deformation, serious lattice distortion and grain refinement are more obvious in torsion stage, comparing compression stage.(2) In the study of effect of the anvil structure parameters (depth and angle of cavity) on the plastic deformation of compressed pure copper disks, it is found that the degree of inhomogeneous deformation is increased with the increase of depth. And the overall deformation of the sample is more and more intense. Moreover, the range of DMZ, the radial width of the soft zone and the radial plastic flow distance are increasing. With the increase of the angle of cavity, the degree of inhomogeneous plastic deformation of compressed disks decrease, and the deformation gradually becomes stable. In addition, the range of DMZ, the radial width of the soft zone and the radial plastic flow distance are reduced.(3) The effect of friction on the plastic deformation and the lagging deformation on the upper and bottom surface of HPT processed disks were investigated. The results indicates that the overall deformation of HPT processed disks and the degree of inhomogeneous deformation are increased as the friction coefficient increasing, whatever in compression stage or torsion stage. Moreover, the hardness hill, DMZ and soften region are changed as the friction changing. In addition, the lagging deformation on the upper and bottom surfaces of HPT processed disks was founded, and the plastic deformation on the upper surface is lagging that on the bottom surface. This lagging deformation is probably due to the contributions of different actions of the two dies and the friction between disk and dies during HPT process.Moreover, the range of lagging deformation zone is close to the edge zone as the number of revolution increasing.