Densification mechanism and mechanical properties of tungsten powder consolidated by spark plasma sintering

The dominant densification mechanism of a tungsten powder processed by spark plasma sintering (SPS) is revealed by the continuum theory of sintering-based regression of the experimental data on the powder consolidation carried out at the temperatures from 1600 °C to 1800 °C and pressure levels of 60 MPa and 120 MPa. The strain rate sensitivity is determined to be 0.39 and the sintering activation energy is 412-433 kJ/mol. It appears that the main mechanism of tungsten powder densification compaction is grain boundary sliding controlled by dislocation climb with the dislocations moving along grain boundaries. The evidence of the superplastic-like behavior of the tungsten powder during SPS is also supported by electron backscatter diffraction microstructure analysis of the compacted specimens. The relative density of the compacted pellets reaches 81-95%, depending on the SPS conditions. The experimental outcomes indicate that the carbon uptake during SPS results in the formation of tungsten carbide at the surface of compacted specimens. Based on the experimental data, the diffusion coefficient of carbon in tungsten is obtained and is found to be similar to literature values.