Tungsten carbide is a composite material prized across numerous industries for its extreme durability and strength. Often referred to simply as “carbide” or “hardmetal,” this ceramic-metal compound is dense and gray. It finds extensive application in the production of high-performance cutting tools, industrial wear parts, and durable jewelry.
The Primary Ingredients
Tungsten carbide is formed from two elements: tungsten (W) and carbon (C). Tungsten is a rare metal known for its exceptionally high melting point, making it a heavy and refractory base material that provides the bulk of the material’s inherent strength and density. Carbon is introduced, often as carbon black or graphite, to chemically bond with the tungsten. These powdered elements react together at high temperatures, typically \(1,400^{\circ}\text{C}\) to \(2,000^{\circ}\text{C}\), to form tungsten carbide (WC) powder in a process known as carbiding.
Pure tungsten carbide is extremely hard but inherently brittle. To overcome this limitation, the final product is engineered as a composite material known as cemented carbide. This material requires a metallic binder to act as a tough matrix, typically using cobalt (Co) or, less frequently, nickel (Ni). The binder content usually ranges from 3% to 16% of the final product’s weight, depending on the desired balance between hardness and toughness.
Transforming Powder into Product
The production of cemented tungsten carbide relies on powder metallurgy. This process begins after the initial WC powder has been synthesized through the high-temperature carbiding reaction. The fine, gray WC powder is then blended with the powdered metallic binder, often cobalt, along with small amounts of organic additives.
This blending stage uses specialized mills to ensure a homogeneous mixture of the hard WC grains and the softer binder metal. Achieving a uniform distribution is paramount, as the binder must coat every carbide particle to create a durable composite. After mixing, the powder is pressed into the desired shape, known as a “green compact,” using high-pressure dies or isostatic pressing methods.
The green compact is fragile and must undergo a final, transformative step called sintering. Sintering heats the compact to temperatures between \(1,400^{\circ}\text{C}\) and \(1,600^{\circ}\text{C}\) in a vacuum or inert atmosphere. This temperature is below the melting point of the tungsten carbide but above the melting point of the metallic binder.
The high heat causes the cobalt binder to liquefy, wetting the surfaces of the solid tungsten carbide grains. The liquid binder dissolves a small amount of the WC, which then precipitates out, resulting in the fusion and densification of the entire structure. As the material cools, the metallic binder solidifies, cementing the hard carbide particles into a solid, dense, and tough composite material.
The Resulting Physical Properties
Tungsten carbide possesses a set of exceptional physical characteristics. Its most celebrated property is its extreme hardness, which is second only to diamond and cubic boron nitride. The typical Vickers hardness value for cemented carbide can range up to 2600 HV, making it highly resistant to scratching and deformation.
The presence of the heavy tungsten element results in a remarkably high density, often falling between 13 and \(15\text{ grams per cubic centimeter}\). This high density is a key factor in its use for applications requiring mass, such as kinetic energy penetrators and counterweights. Furthermore, the material exhibits a high modulus of elasticity, meaning it is exceptionally rigid.
Tungsten carbide is approximately three times as stiff as steel, with a Young’s modulus generally between \(530\text{ and }700\text{ GPa}\). This rigidity allows it to maintain its shape under immense pressure without bending or deflecting.