Kinetic Analysis of Densification Behavior of Nano-sized Tungsten Powder

The densification behavior of nano-sized tungsten powder is examined using both nonisothermal and isothermal methods, and the kinetics of densification is evaluated using conventional sintering theories. The results show that nano-sized powder, similar to micrometer-sized powder, experiences three stages of sintering: initial, intermediate, and final. The initial densification of nano-sized powder increased linearly with increasing time. The rate of densification accelerated after the compact reached above 50% relative density. The initial densification (when relative density <50%) was found to be the result of particle coarsening induced particle rearrangement. The apparent linear initial densification behavior is postulated to be due to the linear kinetic behavior of coarsening. Furthermore, surface diffusion can contribute to the initial densification of nano-sized powder indirectly by being the primary mass transport mechanisms of the coarsening at the beginning of the sintering. The intermediate and final stages of nano sintering have similar densification behavior to those of micrometer-sized powders, during which grain-boundary diffusion is the main mechanism of densification.