Effect of Carbon Sources and Carbonaceous Atmospheres on the Effective Synthesis of Nanostructured Tungsten Carbide Powders

Abstract

Owing to its ultra-fine microstructure, nanostructured tungsten carbide (WC) powders characterized by advanced mechanical properties are of highest in terest for the metal cutting industry where they are used for the production of cemented carbide cutting tools. In this work, WC synthesis from precursor mixes containing tungsten powder (in form of W or WO3 powder) and carbon sources (as graphite orcarbon black) is achieved by a two-step process. Mechanical activation by ball milling of the precursor powders is followed by thermal activation at 1100°C for 30 min in Ar or Ar-10%CO atmospheres. Depending on the tungsten source (W or WO3 powder) solid carbon provides either solely carburization, or both reduction and carburization, which can be assisted by the presence of CO in the synthesis atmosphere. The results show that homogeneous, fine mixes of the base powders after milling offer large contact area and improve reactivity between the precursors. Synthesis of pure WC powders is achieved at 1100 ⁰C in inert Ar atmosphere when using metallic tungsten as precursor. Using oxide precursors (WO3), synthesis is not completed at 1100 ⁰C in Ar atmosphere, however, a significant improvement in the efficiency of the synthesis is achieved when using Ar-10%CO atmospheres. Although the reducing activity of CO seems to be low in the conditions studied in this work, improved carburization of metallic tungsten by CO might be the key for improving efficiency of the synthesis process.