The sintering behavior of quasi-spherical tungsten nanopowders

• Quasi-spherical and well-dispersed tungsten nanopowders exhibited high sintering activity.
• 91.3% of theoretical density was achieved with fine grain size of 1.98 μm.
• Extremely high Vickers microhardness of 606 VHN was obtained.
• Quasi-spherical nanopowders showed the two-step grain growth process.

In this work, the sintering behavior of quasi-spherical tungsten nanoparticles was investigated by analysis the sintered compacts obtained at different sintering temperatures and dwell time, and the influence of microstructures on the density and Vickers microhardness of sintered products was also studied. Experimental results show that particle shape and size distribution are critical to the sintering activity and mechanical properties of obtained compacts. 91.3% of theoretical density (TD) of the compact could be obtained at low sintering temperature of 1500 °C, and the highest hardness of 606 VHN could be achieved when sintered at 1100 °C due to formation of uniform, densely packed sintered compacts with grain size of 235.7 nm. Importantly, unusual linear correlation between grain size and relative density was observed in our experiment, and a cut-off point exists at 85.6% of TD. The kinetic analysis revealed that surface diffusion is responsible for the mass transport during the initial sintering stage.