Al2O3–WC synthesis by high-energy reactive milling

Like most carbide-based composites, the two main characteristics of alumina–tungsten carbide (Al2O3–WC) composites are high hardness and high wear resistance. These features confer the composites important engineering applications, in particular when they are used as cutting tools. The present research involved a study of Al2O3–WC nanometric powders obtained through reactive milling. In this process, high-energy milling promotes the reaction in a mixture of reactive powders. The material was milled in a high-energy SPEX 8000 Mixer/Mill, using WO3, Al and C precursor powders. The highly exothermic self-propagating high-temperature synthesis (SHS) type reaction was self-sustained, producing a temperature peak that was detected by a thermocouple attached to the external surface of the vessel. Using stoichiometric proportions of the reagents to reduce the WO3 and to obtain WC, and adding Al2O3 as diluent, the SHS reaction occurred up to a limit of 0.8 mols of diluent, forming not only alumina but also a W2C mixture with little WC. To obtain only WC it was required the addition of more than 0.8 mols of C, which indicates that the reaction may have occurred through a gaseous phase reaction mechanism.