Production of WC–15Co Ultrafine-Grained Hard Alloy from Powder Obtained by the Electroerosive Dispersion of VK15 Alloy Wastes in Water

Abstract

In this paper we study the possibility of producing a WC–15Co ultrafine-grained hard alloy (HA) from a powder obtained by the electroerosive dispersion (EED) of wastes of a VK15 HA in water. As a result of the EED of the alloy in the oxygen-containing liquid, the carbon concentration in the resulting powder decreases from 5.3 to 2.3%. When the powder is heated to 900°C in a vacuum, the carbon content drops to 0.2% due to the presence of oxygen. The resulting powder includes WC, W2C, and Co phases. The particles have a dendritic structure consisting of newly formed tungsten-containing grains and cobalt interlayers. In this study, the controlled removal of oxygen and the replacement of carbon in the powder were performed under heating in a CO atmosphere to t = 900°C. The processed powder has the required phase composition (WC + Co) and contains 5.3% carbon. The particles retain their spherical shape after carbon replenishment. The WC grains in the particles acquire a lamellar configuration, the space between which is filled with cobalt. The average grain diameter was found to be smaller than that in the initial alloy. As a result of sintering the powder in vacuum at 1390°C, a WC–15Co ultrafine-grained HA is obtained, the average diameter of WC grains in which is 0.44 μm, which is several times smaller than that in the initial alloy (1.8 μm). In this case, most of the grains retain their lamellar shape. Due to the fineness and 15% cobalt content, the resulting alloy has high hardness (1620 HV), fracture toughness (13.2 MPa m1/2), and strength (1920 MPa). In terms of the set of characteristics, this material is not inferior to analogs obtained by other methods.