Microwave sintering: A new approach to fine-grain tungsten - II

While grain-growth inhibition in micrograined refractory metals and ceramics is well documented, a reduction in grain size to the nanoscale is relatively new. In the work reported here, nanocrystalline tungsten powders containing small amounts of HfO₂ and Y₂O₃ as dopants were synthesized using a solution-synthesis technique. The assynthesized powders were then consolidated using microwave sintering. The effect of dopant concentration on the crystallite size, particle size, and grain size of the sintered material was monitored. Average grain sizes as low as 0.5 μm were achieved in doped microwave-sintered tungsten; this grain size is substantially smaller than previously reported, namely ∼2 μm in undoped tungsten. It was also observed that an optimum level of dopant exists for effective grain-growth inhibition, since the sintering of tungsten is hindered at higher dopant levels.