Tungsten carbide can exist in two phases; WC and W2C, and have a hardness of 2000 – 2700 HV. Tungsten carbide powders come as monocristalline WC with a carbon content ≈ 6, 1% or eutectic WC/W2C with a carbon content ≈4% as seen in a carbon – tungsten phase diagram.

Figure 1 shows the tungsten-rich part of the binary W-C equilibrium diagram.

Three W-C stoichiometries have been found, hexagonal W2C crystallizing in three modifications, the PbO2, Fe2N, and CdI2 types, denoted β, β’, and β”, respectively, the cubic sub-carbide WC1-x crystallizing in the NaCl type structure denoted γ, and the hexagonal WC denoted δ. W2C exhibits a comparatively wide homogeneity range of 25.5 to 34 at.% C at 2715°C.

This phase originates from a eutectoidal reaction between elemental W and δ-WC at 1250°C and melts congruently with the W solid solution at 1715 ±5°C and with γ-WC1-x at approximately 2758°C. Phases of W2C stoichiometry are obtained as intermediate products during WC production. The γ-phase results from a eutectoidal reaction between β and δ at 2535°C and melts at approximately 2785°C. It can be obtained at room temperature by extremely rapid cooling, e.g., in plasma sprayed layers. The technically important δ-WC is the only binary phase stable at room temperature and has almost no solid solubility up to 2384°C but may become carbon deficient between this temperature and its incongruent melting point.

What is tungsten carbide in chemistry?

. It is prepared by heating powdered tungsten with carbon black in the presence of hydrogen at 1,400°–1,600° C (2,550°–2,900° F).