Fabrication of nanocrystalline WC powders by mechanical alloying of elemental powders

Abstract

Tungsten carbides have been widely used for wear resistant materials in forms of cemented carbides with binder and binderless cemented carbides. Nanocrystalline WC powders were fabricated from elemental powders of W and carbon black by mechanical alloying process. The transition of microstructure and phases in powders during the mechanical alloying process were analyzed by XRD, XPS and TEM. The grain size of W was continuously decreased with increasing the milling time and reached to a constant value of about 20nm after 2hours of mechanical alloying. WC phase was start to be formed after 10 hours of mechanical alloying. The XRD analysis showed that the full conversion into WC phase was obtained after about 24 hours of mechanical alloying. The mechanical alloying process could be divided into 4 steps - cell formation, nanocrystalline W grain formation, WC formation initiation and fully reacted to WC - based on the analysis of microstructure and constituent phases. The grain size of WC synthesized by mechanical alloying was was much finer than that fabricated by spray conversion process.