On sinterability of nanostructured W produced by high-energy ball milling

The present investigation reports for the first time a dramatic decrease in the sintering temperature of elemental W from the conventional temperature of >= 2500 degrees C to the modest temperature range of 1700-1790 degrees C by making the W powder nanostructured through high-energy mechanical milling (MM) prior to sintering. The crystallite size of the initial W powder charge with a particle size of 3-4 mu m could be brought down to 8 nm by MM for 5 h in WC grinding media. Further milling resulted in a high level of WC contamination, which apparently was due to work hardening and the grain refinement of W. A sintered density as high as 97.4% was achieved by sintering cold, isostatically pressed nanocrystalline (8 nm) W powder at 1790 degrees C for 900 min. The microstructure of the sintered rods showed the presence of deformation bands, but no cracks, within a large number of W grains. The mechanical properties, when compared with the hardness and elastic modulus, of the sintered nano-W specimen were somewhat superior to those reported for the conventional sintered W.