Tungsten Carbide Structure Properties Preparation and Applications

Tungsten carbide is a chemical compound comprising equal parts of tungsten and carbon atoms. In its most simple form, tungsten carbide is a fine grey powder, but it can be pressed and shaped into shapes through a method called sintering for use in industrial equipment, cutting tools, abrasives, armour-piercing shells and jewellery. We have covered all of the important aspects of tungsten carbide in this article, including its description, tungsten carbide rings, applications, price, and properties. Wedding rings are often made of tungsten carbide. Tungsten carbide rings are much more durable than gold and silver rings. Tungsten rings are rated between 8 and 9 on the Mohs scale of hardness. 

Structure of Tungsten Carbide

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A hexagonal shape of WC exists, as well as a cubic high-temperature form, tungsten carbide, with a rock salt structure. The hexagonal structure is made up of a plain hexagonal lattice of metal atoms of layers lying directly over one another, therefore, not closely packed), with carbon atoms filling half the interstices, giving both tungsten and carbon a normal trigonal prismatic, 6 coordination. The bond lengths between tungsten atoms in a hexagonally packed layer are 291 pm, the shortest distance between tungsten atoms in neighbouring layers is 284 pm, and the tungsten carbon bond length is 220 pm, according to the unit cell dimensions. The length of the tungsten-carbon bond is thus equivalent to the single bond in W(CH3)6 (218 pm), in which tungsten is highly twisted trigonal prismatically coordinated.

Properties of Tungsten Carbide

Physical Properties of Tungsten Carbide

• Tungsten carbide has a high melting point of 2,870°C (5,200°F).

• It has a boiling point of 6,000°C (10,830°F).

• When heated to 1 atmosphere (100 kPa), the thermal conductivity of 110 Wm^-1K^-1.

• It has a coefficient of thermal expansion of 5.5 µm·m^-1·K^-1.

• Tungsten carbide is extremely stiff, with a Mohs hardness of 9 to 9.5 and a Vickers hardness of about 2600. 

• Young's modulus is around 530–700 GPa, the bulk modulus is around 630–655 GPa, and the shear modulus is around 274 GPa. 

• It has a Poisson's ratio of 0.31 and has an ultimate tensile strength of 344 MPa, an ultimate compressive strength of around 2.7 GPa.

• A longitudinal wave (sound) travelling through a thin rod of tungsten carbide travels at 6220 m/s. 

• The low electrical resistivity of tungsten carbide (about 0.2 m) is equivalent to that of other metals (e.g. vanadium 0.2 m).

• Both molten nickel and cobalt readily wet tungsten carbide. The phase diagram of the W-C-Co system reveals that WC and Co have a pseudo-binary eutectic.

• Controlling the carbon content in WC-Co cemented carbides is critical due to the potential for carbides to form and the brittleness of these phases.

• In the presence of a molten phase, such as cobalt, abnormal grain growth has been observed in the sintering of tungsten carbide, with significant implications for the product material's efficiency.

Chemical Properties Tungsten Carbide

• There are two well-known tungsten and carbon compounds: WC and tungsten semicarbazide, W₂C. Coatings may contain both substances, with the proportions varying depending on the coating process.

• By heating the WC phase to high temperatures with plasma and then quenching in inert gas, another meta-stable tungsten and carbon compound can be produced (plasma spheroidization).

• The non-stoichiometric high-temperature phase WC1-x  exists in a meta-stable form at room temperature as a result of this process, which causes macrocrystalline WC particles to spheroidize. As compared to other tungsten carbide compounds, this phase's fine microstructure offers high hardness (2800-3500 HV) and strong toughness. Because of this compound's meta-stability, it has lower high-temperature stability.

• At high temperatures, WC decomposes into tungsten and carbon, which can happen during high-temperature thermal sprays, such as in HVOF and HEP methods.

• At 500–600 °C (932–1,112 °F), WC begins to oxidise. It is acid-tolerant and is only targeted at room temperature by hydrofluoric acid/nitric acid (HF/HNO₃) mixtures. It is unreactive to dry H₂ up to its melting point and reacts with fluorine gas at room temperature and chlorine above 400 °C or 752 °F. In aqueous hydrogen peroxide solutions, finely powdered WC readily oxidised. It reacts with aqueous sodium carbonate at high temperatures and pressures to form sodium tungstate, which is used to recover scrap cemented carbide due to its selectivity.

Synthesis of Tungsten Carbide

Tungsten carbide is made by reacting tungsten metal with carbon at temperatures between 1400 and 2000 degrees Celsius. A proprietary lower temperature fluid bed process that reacts to tungsten metal or blue WO₃ with CO/CO₂ mixture and H2 between 900 and 1200 °C is one of the other methods.

WC can also be made by heating WO₃ with graphite at 900 degrees Celsius directly or in hydrogen at 670 degrees Celsius followed by carburization in argon at 1000 degrees Celsius. The following chemical vapour deposition methods have been investigated:

At 670 °C (1,238 °F), tungsten hexachloride is reacted with hydrogen (as a reducing agent) and methane (as a carbon source).

WCl₆ + H₂ + CH₄ → WC + 6 HCl

At 350 °C (662 °F), tungsten hexafluoride is reacted with hydrogen (as a reducing agent) and methanol (as a carbon source).

WF₆ + 2 H₂ + CH₃OH → WC + 6 HF + H₂O

Uses of Tungsten Carbide

Cutting Tools for Machining

Cutting tools made of sintered tungsten carbide are extremely abrasion-resistant and can withstand higher temperatures than normal high-speed steel (HSS) tools. Carbide cutting surfaces are often used for machining carbon steel and stainless steel, as well as in applications where steel tools will wear out easily, such as high-volume and high-precision manufacturing. Carbide tools provide a better finish on parts than steel tools because they hold a sharp cutting edge longer, and their temperature tolerance allows for faster machining. Cemented carbide, solid carbide, hard metal, and tungsten-carbide cobalt are common names for the element. It's a metal matrix composite in which the aggregate is tungsten carbide particles and the matrix is metallic cobalt. Rotary Carbide Burrs, also known as rotary files or die grinder pieces, are used to cut, shape, and grind as well as remove sharp edges.

Ammunition

Tungsten carbide is commonly used in armour-piercing ammunition, either as a monolithic sintered type or as a tungsten carbide cobalt composite, particularly where depleted uranium is not available or is politically unacceptable. Tungsten carbide was only used in the production of machine tools and a limited number of projectiles. Due to its combination of high hardness and density, it is an efficient penetrator.

The sabot form of tungsten carbide ammunition is now the most popular. One of the most common forms of saboted small arms ammunition is SLAP, or saboted light armour penetrator, in which a plastic sabot is discarded at the barrel muzzle. Non-discarding coats, regardless of material, are viewed as bullets rather than sabots. Both designs, on the other hand, are popular in light armour-piercing small arms ammunition.

Mining and Foundation Drilling

Top hammer rock drill bits, downhole hammers, roller-cutters, longwall plough chisels, longwall shearer picks, raiseboring reamers, and tunnel boring machines are all made of tungsten carbide. It's most commonly used as a button insert, placed in a steel matrix that serves as the bit's substance. The softer steel matrix holding the tungsten carbide button wears away as well, revealing more of the button insert.

Nuclear

Tungsten carbide is also a good neutron reflector, which is why it was used in early nuclear chain reactions research, particularly for weapons. On August 21, 1945, at Los Alamos National Laboratory, Harry Daghlian dropped a tungsten carbide brick onto a plutonium sphere known as the demon heart, causing the subcritical mass to go supercritical with the reflected neutrons, resulting in a criticality accident.

Sports Usage

Many hikers use trekking poles for balance and to relieve pressure on their leg joints. Carbide tips achieve traction when placed on hard surfaces and last much longer than other forms of tips.

Rollerski tips are commonly made of carbide, while ski pole tips aren't so they don't need to be as hard to crack through layers of ice. Many skiers use roller skiing to practise during the summer months because it resembles cross-country skiing.

Snowmobiles' drive tracks can be inserted with sharpened carbide tipped spikes, also known as studs. On ice surfaces, these studs improve traction. Under each snowmobile ski, longer v-shaped segments fit into grooved rods called wear carbide rods. On harder ice surfaces, the relatively sharp carbide edges improve steering. If the snowmobile has to crossroads or other abrasive surfaces, the carbide tips and segments minimise wear.

Tungsten carbide studs in vehicle, motorcycle and bicycle tyres improve traction on ice. Steel studs are commonly favoured because of their superior wear resistance.

Traction Improving Device

Tungsten carbide is often used in farriery or horseshoeing, to increase traction on slick surfaces like roads or ice. To mount the shoes, carbide-tipped hoof nails can be used; in the United States, borium – tungsten carbide chips in a matrix of softer metals like bronze or mild steel – can be welded to small areas of the shoe's underside before mounting. Different types of tungsten metal prices can be easily found on various e-sites.

Surgical Instruments

Surgical devices made of tungsten carbide are used in open surgery (scissors, forceps, hemostats, blade-handles, and so on) and laparoscopic surgery (graspers, scissors/cutter, needle holder, cautery, and so on). They are more expensive than stainless-steel equivalents and need more delicate handling, but they work better.

Jewellery

Tungsten Carbide Ring- Due to its extreme hardness and high scratch resistance, tungsten carbide, usually in the form of cemented carbide (carbide particles brazed together by metal), has become a common material in the bridal jewellery industry. Even though it has high impact resistance, its extreme hardness means it can be broken in some conditions. Some people think this is useful because a tungsten ring will crumble in an impact, allowing it to be easily removed, while precious metals would bend flat and need cutting. The hardness of tungsten carbide is about ten times that of 18k gold. Consumers are drawn to it because of its advanced nature, in addition to its design and high finish. If a ring must be removed quickly, special tools, such as locking pliers, may be needed (e.g. due to a medical emergency following a hand injury accompanied by swelling). Tungsten rings price is not overly costly, but the consistency varies.

Types of Tungsten Ring

• Tungsten rings for men

• Tungsten rings for women

• Black tungsten rings

• Diamond tungsten ring

• Wood tungsten ring

• Exotic tungsten ring

Did you know that?

• The spinning ball in the tips of ballpoint pens that disperses ink during writing is made of tungsten carbide.

• Tungsten carbide is a common material used in the manufacture of gauge blocks, which are used in dimensional metrology to produce precise lengths.