Tungsten is a metal known for its unique properties, making it valuable in various industrial applications. It possesses the highest melting point of all metals, reaching approximately 3,422 degrees Celsius (6,192°F), allowing it to maintain strength and stiffness at extremely high temperatures. It is also notably dense, comparable to gold. These characteristics contribute to its outstanding hardness, a property that sets it apart from many other materials.
Understanding Material Hardness
Material hardness describes a material’s ability to resist localized permanent deformation, such as scratching, indentation, or abrasion. It indicates how a material performs under mechanical stress and wear. Various methods are employed to measure hardness, each focusing on slightly different aspects of resistance.
One common method is the Mohs hardness scale, which assesses a material’s relative resistance to scratching. This qualitative scale ranges from 1 (softest, like talc) to 10 (hardest, like diamond), determining if one material can scratch another.
Another widely used measurement is Vickers hardness, which evaluates a material’s resistance to indentation. This test involves pressing a diamond indenter, shaped like a square-based pyramid, into the material’s surface under a specific load. The Vickers Pyramid Number (HV) is then calculated based on the size of the resulting indentation.
The Rockwell hardness test also measures indentation hardness but differs in its approach. It applies a minor load followed by a major load, and the hardness value is determined by the depth of the indenter’s penetration. Rockwell testers often provide a direct reading.
The Exceptional Hardness of Tungsten
Tungsten exhibits remarkable hardness, particularly in its pure form and as an alloy. Pure tungsten has a Mohs hardness of approximately 7.5. This places it significantly above many common metals on the scale.
When alloyed with carbon to form tungsten carbide, its hardness increases even further, often reaching 8 to 9 on the Mohs scale. This is similar to sapphire (9) and approaches diamond (10), the hardest natural material. This makes tungsten carbide exceptionally resistant to scratching.
On the Vickers scale, pure tungsten typically has values ranging from around 350 HV to 430 HV. Tungsten carbide, however, demonstrates even higher Vickers hardness, with values often exceeding 1600 HV and some forms reaching between 2800 HV and 3500 HV. For comparison, mild steel has a Vickers hardness of about 160 HV.
Tungsten’s inherent hardness stems from its strong metallic bonds and compact atomic structure. Its unique electron configuration contributes to its stability and resistance to deformation. When combined with carbon to form tungsten carbide, it creates a very dense crystal structure, further enhancing its properties.
Applications Driven by Hardness
Tungsten’s extreme hardness makes it indispensable in applications requiring exceptional resistance to wear and deformation. Its use in cutting tools is widespread, with tungsten carbide being a primary material for drills, saw blades, and machining inserts. These tools maintain their sharp edges and structural integrity under intense cutting forces, allowing for efficient material removal.
The military also leverages tungsten’s hardness and density in armor-piercing projectiles. Tungsten alloys are used as penetrators in ammunition designed to breach hardened targets like armored vehicles. Their concentrated kinetic energy allows them to punch through protective layers.
Tungsten and its alloys are found in various wear-resistant components within machinery. These include parts subjected to significant abrasion, impact, and pressure, such as industrial liners, plates, and bearings. Its ability to withstand continuous friction and mechanical stress prolongs equipment lifespan. Tungsten is also suitable for electrical contacts, resisting wear from repeated opening and closing.
Working with Tungsten’s Extreme Hardness
Despite its remarkable hardness, tungsten presents specific challenges in manufacturing and application due to its inherent properties. Pure tungsten is brittle at room temperature, meaning it can crack or fracture easily under stress rather than bending or deforming. This brittleness can limit its suitability for applications that require impact resistance or flexibility.
This characteristic makes machining and forming tungsten particularly difficult. Traditional cutting and shaping methods often prove ineffective because tungsten’s hardness causes rapid wear on conventional tools. Specialized techniques such as grinding, electrical discharge machining (EDM), or laser cutting are typically required to process it.
Tungsten’s high melting point, while advantageous for high-temperature applications, also complicates its processing. It is often manufactured through powder metallurgy and sintering, where powder is compacted and heated to fuse particles, rather than being melted and cast. This combination of properties necessitates specialized processing approaches.