An Investigation of the System: Wolfram - Colbalt - Carbon

The phases and phase equilibria in the system wolfram-cobalt-carbon have been studied by x-ray diffraction methods, metallographic technique and thermal analysis. An x-ray method is introduced for evaluating compositions and amounts of phases. Diwolfram carbide is shown to possess a defect lattice with 8-21 percent of unoccupied carbon sites. Monowolfram carbide indicates a very narrow range of homogeneity. In addition to the carbide Cosub 3WaC, reported previously the existence of double carbides Cosub 3Wsub 6Csub 2 and Cosub 3Wsub 10Csub 4 is revealed. Isomorphous carbides are shown to form in corresponding iron and nickel systems. The lattices are solved and the constants measured. The carbide Cosub 3Wsub 3C is shown to be stable, whereas monowolfram carbide is found to be metastable in alloys where wolfram-cobalt ratio is less than one. Tentative diagrams of stable and metastable equilibrium in the system wolfram-cobalt-carbon are proposed. The basic reactions in sintering of cobalt cemented wolfram carbides are explained.