Tungsten carbide is a composite material celebrated for its extreme durability, which is often considered second only to diamond among commercially used compounds. The material, represented by the chemical formula WC, is primarily formed by combining tungsten and carbon atoms. This combination creates a dense, powder-like ceramic that is then typically sintered with a metal binder, most commonly cobalt, to create a cemented carbide structure. Its durability is complex, depending not only on its inherent strength but also on the specific type of stress it encounters.
Measuring Extreme Hardness
Tungsten carbide’s reputation for durability stems from its extraordinary hardness—the material’s resistance to scratching, abrasion, and surface deformation. On the Mohs scale of mineral hardness, tungsten carbide scores between 8.5 and 9, making it one of the hardest materials available for commercial use. This places it far above common metals like hardened steel, which typically scores around 4.5 to 6.5. The material’s resistance to surface wear is so high that it can last up to 100 times longer than steel under abrasive conditions. This property is a direct result of its rigid atomic structure, which maintains its shape even under extreme compressive forces exceeding 600,000 pounds per square inch.
Understanding its Vulnerability to Impact
While tungsten carbide boasts exceptional hardness, its durability profile has a significant counterpoint: brittleness. Brittleness is the tendency to fracture or shatter when subjected to sudden, sharp impact, unlike toughness, which is the ability to absorb energy before fracturing. Since tungsten carbide is a ceramic-metal composite, it has low fracture toughness compared to ductile metals. If struck with a hammer or dropped, it could chip or shatter completely, especially if the impact is focused on a small area. Although the metallic binder, usually cobalt, helps improve its toughness somewhat, the material still lacks the resilience of traditional metals and is not well-suited for applications involving unpredictable mechanical shock.
Resistance to Wear and Chemical Breakdown
Beyond mechanical stress, tungsten carbide demonstrates remarkable durability against environmental degradation. The compound exhibits excellent chemical stability, resisting reaction with most common acids, bases, and corrosive agents. This stability prevents the material from rusting or suffering the progressive corrosion common in many pure metals.
The material also maintains its structural integrity across a wide temperature range. Tungsten carbide has an extremely high melting point, remaining stable up to approximately 2,870 degrees Celsius (5,198 degrees Fahrenheit). This thermal stability allows it to maintain its hardness and resist oxidation up to about 500 to 600 degrees Celsius in an oxidizing atmosphere. While exposure to certain potent oxidizers, like a mixture of hydrofluoric and nitric acid, can eventually cause breakdown, tungsten carbide is nearly indestructible in standard environmental conditions.