The Simulation And Experimental Investigation On Pure Tungsten By Severe Plastic Deformation

As a kind of important strategic metals, tungsten owns the highest melting point and boiling point of all the metals, meanwhile it has many other kinds of excellent properties, such as the lowest thermal expansion coefficient, good heat resistance, high compression modulus and elasticity modulus, and so on. Industrial tungsten can only be obtained by powder metallurgy method, and the application of tungsten is seriously limited because it have many problems, for instance, coarse grain, a lot of pore and impurity, low density, and the poor strength toughness. Ultrafine grain structure could be obtained through severe plastic deformation (SPD) at lower temperature, so equal channel angular pressing (ECAP) and multi-directional forging (MDF) get a lot of attention due to its remarkable effect.In this paper, the pure tungsten powder's ECAP model was built through discrete element method (DEM), numerical simulation work was done using the PFC software, and particle deformation, velocity distribution, chains of contact force were studied. After one pass ECAP, particle cluster's tensile direction have an angel Of 26.5° to the horizontal direction. The mould fillet has very big inhibition on the particles, velocity and contact force will decrease through this area. Heat generated by plastic deformation is the main cause of temperature increase. The density is improved during the process. The incompressible rigid-plastic material model of pure tungsten was established in the Deform software, the finite element simulation of deformation process was done, through the comparison and analysis, the optimum parameters of the experiment was determined.ECAP and MDF experiment of pure tungsten powder were carried out at relatively low temperature, and the optical microscope, scanning electron microscope, measurement of relative density and microhardness testing methods were used to study the density behavior and consolidation mechanism during the deformation process. The results showed that reunion phenomenon of the pure tungsten powder disappears after one pass ECAP, and porosity decreased significantly. After two passes MDF deformation, the consolidation was generated between powder particles. The high pressure provided by SPD can significantly increase the sintering stress, decrease the densification temperature, and in this way can limit grain growth.