Production of WC-15Co ultrafine-grained hard alloy from powder obtained by VK15 alloy waste spark erosion in water

Abstract

The study covers the possibility of WC-15Co ultrafine cemented carbide production from powder obtained by spark erosion (SE) of VK15 cemented carbide waste in water. As a result of SE in an oxygen-containing liquid (H2O), the carbon content in the resulting powder decreases from 5.3 to 2.3 %. When the powder is heated to 900 °C in vacuum, the carbon content decreases to 0.2 % due to the presence of oxygen. The powder obtained consists of WC, W2C and Co phases. Particles have a dendritic structure consisting of newly formed tungsten-containing grains and cobalt interlayers. The controlled removal of oxygen and carbon replenishment in the resulting powder were carried out by heating in the CO atmosphere to t = = 900 °C. The processed powder has a required phase composition (WC + Co) and carbon content (5.3 %). Particles retain their spherical shape after carbon replenishment. WC grains in particles become plate-shaped with the space between them filled with cobalt. The average grain diameter is smaller than in the initial alloy. The vacuum sintering of the resulting powder at 1390 °C made it possible to obtain WC–15Co ultrafine-grained cemented carbide with an average WC grain diameter of 0.44 μm. It is several times smaller than the average grain diameter in the initial alloy (1.8 μm). Most grains retain their plate shape. The resulting alloy combines high hardness (1620 HV), increased fracture toughness (13.2 MPa·m1/2) and strength (1920 MPa) due to its fine-grain structure and 15 % cobalt content. In terms of the set of its properties, this alloy is not inferior to analogues obtained by other methods.