Fabrication and characterizations of new nanocomposite WC/Al_2O_3 materials by room temperature ball milling and subsequent consolidation

摘要

Reactant material powders of pure WO_3, Al and graphite have been milled at room temperature using a high-energy ball mill. After a few kiloseconds of milling (11 ks), numerous fresh surfaces of the reactant materials are created as a result of the repeated impact and shear forces which are generated by the balls. After 43 ks of milling, a mechanical solid state reduction is successfully achieved between the fresh Al and WO_3 particles to form a product of nanocrystalline mixture of Al_2O_3 and W powders. A typical mechanical solid state reaction takes place between the W particles and graphite powders to obtain fine grains of nanocrystalline WC. Towards the end-stage of ball milling (360 ks the nanocrystalline WC grains (5 nm) are embedded into the fine matrix of Al_2O_3 to form fine nanocomposite powders (less than 1 mu m in diameter) of WC-32 at.percent Al_2O_3 material with spherical-like morphology. This composite powder was then consolidated under vacuum 1963 K, with a pressure ranging from 19.6 to 38.2 MPa for 0.3 ks, using a plasma activated sintering method. The consolidation step does not lead to a dramatic grain growth and the compacted samples that are fully dense still maintain their unique nanocrystalline characteristic The elastic properties and the hardness of both the consolidated samples have been investigated. A model for fabrication of new refractory nanocomposite WC/Al_2O_3 materials at room temperature is proposed.