Fabrication of Ultra-fine Grain Tungsten by Combining Spark Plasma Sintering with Resistance Sintering under Ultra High Pressure

Pure tungsten with ultra-fine grains has been fabricated by two novel sintering methods, namely spark plasma sintering (SPS) and resistance sintering under ultra high pressure (RSUHP). The sample fabricated by SPS at 1600 °C has a high density of 97.8% and tightly bound grains. However, during the SPS process the W grains obviously grew. On the contrary, the sample fabricated by RSUHP has a low density and weakly bound fine grains. The disadvantages in both the techniques can be avoided via combining the two methods by fabricating green compacts using SPS at 1400 °C followed by consolidating that by RSUHP. By employing the combined method, the product with a relative density of more than 99% and an average grain size less than 400 nm can be obtained. The consolidating mechanism has been explored and the process has been optimized. In addition, any rare earth metal element additives to prevent grains from growing are not needed during the sintering process.