Tungsten Carbide Metals: Part One

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Introduction to Tungsten Carbide

Tungsten Carbide combines tungsten, the metal with the highest melting temperature among metallic elements, with carbon. This combination forms a refractory carbide with superior properties such as extreme hardness (2000–2700 HV) and excellent chemical resistance. Tungsten Carbide exists in two primary phases, WC and W2C, each with distinct characteristics and uses.

Tungsten Carbide Phases and Properties

Tungsten Carbide powders are typically found as monocristalline WC with a carbon content of approximately 6.1%, or as eutectic WC/W2C with about 4% carbon, as illustrated in the tungsten-carbon phase diagram (Figure 1).

Three main stoichiometries include:

• W2C: Exhibits a wide homogeneity range (25.5–34 at.% C at 2715°C) and forms from a eutectoidal reaction between elemental W and δ-WC at 1250°C. It melts congruently with the W solid solution at 1715°5°C.
• γ-WC1-x: Results from a eutectoidal reaction between β and δ phases at 2535°C and melts at approximately 2785°C. This phase can be produced at room temperature through rapid cooling.
• δ-WC: The only stable binary phase at room temperature, with no solid solubility up to 2384°C, though it becomes carbon deficient at higher temperatures.

Figure 1: W-C Phase Diagram

This diagram illustrates the tungsten-rich section of the binary W-C equilibrium, detailing the various phases and their formation conditions.

Nominal Properties of Tungsten and Tungsten Carbides

Tungsten Carbide's remarkable attributes make it ideal for demanding applications. Key properties are summarized below in Table 1.

Table 1. Tungsten and Tungsten Carbide Properties

Type	Melting Point	Density
W	3410°C	19.3 [g/cm³]
WC	2870°C	17.2 [g/cm³]
W₂C	2730°C	15.8 [g/cm³]

• High Hardness: 2000–2700 HV
• Melting Point: Exceeds 1800°C
• Chemical Resistance: Good

Applications of Tungsten Carbide

Tungsten Carbide's exceptional properties make it invaluable in various industries:

• Tooling and Mechanical Processing: Used in hard metal tools, often sintered with a metallic binder like cobalt or nickel for enhanced performance.
• Mining Industry: Coats drilling and digging parts to increase durability.
• Agriculture: Applied on plough shares, tillage equipment, and cutters.
• Steel Industry: Serves as coatings for guide rollers.
• Oil Industry: Protects components in high-wear applications.

Surface Coatings and Metal Matrix Composites

Tungsten Carbide is commonly used in surface coatings to enhance wear resistance. Cemented Carbides, formed by sintering tungsten carbide with metallic binders, require cutting and grinding tools of even harder materials like Cubic Boron Nitride (CBN) or diamond discs.

Figure 2: Applications of Tungsten Carbide Coatings

This figure depicts various uses, including coated plough shares, digging equipment, and scrapers, showcasing the versatility and durability of Tungsten Carbide.