Material
Tungsten W
The highest melting point of any metal and roughly the density of gold. Bought for mass in a small volume, for radiation shielding, and for kinetic energy penetrators, where nothing else performs comparably.
Overview
Tungsten is not a structural material in the usual sense. It is specified when a design needs extreme density in limited space, survivability at temperatures that destroy everything else, or shielding against radiation. Its melting point of 3422 degrees Celsius is too high for conventional casting, so mill product is made by pressing and sintering powder and then working it down, which is why the producer list is short and vertically distinct from ordinary metals. In defense it carries two roles no substitute matches well: kinetic energy penetrators, where depleted uranium is the only competitor and carries political cost, and counterweights where density buys balance in a tight envelope.
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Defense applications
Kinetic energy penetrators
Tungsten heavy alloy penetrators convert density and hardness into armor penetration. This is the application that drives most defense tungsten demand and the reason the material is treated as strategically sensitive.
APFSDS long rod penetrators, Armor piercing projectile cores, Fragmentation preforms
Counterweights and ballast
Where mass must sit in a volume too small for lead or steel: rotorcraft blade balance weights, control surface balance, and aircraft trim ballast.
Helicopter rotor balance weights, Control surface counterweights, Aircraft trim ballast, Gyroscope rotors
Radiation shielding and collimation
Tungsten shields at roughly the same effectiveness as lead in substantially less thickness, and without lead's toxicity handling requirements.
Radiation shielding, Collimators, Isotope containers, X-ray targets
High temperature hardware
Rocket nozzle throats, electrodes and furnace hot zones that operate above where any other metal retains useful strength.
Rocket nozzle throat inserts, Furnace hot zones and heat shields, Welding electrodes, Ion thruster grids
Alloys and grades
| Designation | Grade | Class | Notes | Typical forms |
|---|---|---|---|---|
| Pure Tungsten | Unalloyed refractory metal | Sintered and worked unalloyed tungsten. Maximum density, melting point and modulus, at the cost of room temperature brittleness. | Bar and Rod, Plate, Sheet, Wire, Powder | |
| Tungsten Heavy Alloy (WHA) | Liquid phase sintered tungsten-nickel-iron or tungsten-nickel-copper | Tungsten particles bound in a ductile nickel-iron or nickel-copper matrix. Trades a little density for genuine machinability and toughness, which is what makes it usable for real parts. | Bar and Rod, Plate, Castings, Forgings | |
| Thoriated and Lanthanated Tungsten | Dispersion strengthened tungsten | Oxide dispersion raises recrystallization temperature and improves creep resistance and arc starting. Lanthanated grades are increasingly preferred because thoria is mildly radioactive. | Wire, Bar and Rod | |
| Tungsten Carbide | Cemented carbide, cobalt bound | Not a tungsten metal product but the largest use of tungsten by volume. Tungsten carbide particles cemented in cobalt, giving hardness second only to diamond among production materials. | Powder, Bar and Rod |
Properties
| Property | Value | Unit | Note |
|---|---|---|---|
| Density | 19.25 | g/cm3 | 0.697 lb/in3; roughly 2.5 times steel and comparable to gold |
| Melting point | 3422 | degrees C | 6192 degrees F; the highest melting point of any metal |
| Elastic modulus | 400 to 410 | GPa | Roughly double steel; the highest of any commonly used metal |
| Tensile strength, sintered and worked | 550 to 1400 | MPa | Highly dependent on the amount of cold work retained |
| Coefficient of thermal expansion | 4.5 | micrometre/m-K | Very low, and close to some ceramics and silicon, which drives its use in electronic packaging |
| Thermal conductivity | 170 | W/m-K | High for a refractory metal |
| Ductile to brittle transition | Above room temperature | Pure tungsten is brittle at room temperature in the recrystallized condition, which governs how it can be fabricated | |
| Vapor pressure | Lowest of all metals | Why it is used for filaments and vacuum furnace elements |
Advantages
- Highest melting point of any metal, at 3422 degrees Celsius
- Density roughly 2.5 times steel, in a form that is neither toxic nor radioactive
- Highest elastic modulus of any commonly used metal
- Very low thermal expansion, close to silicon and some ceramics
- Excellent radiation shielding at a fraction of lead's thickness, without lead's toxicity
- Retains strength at temperatures where every other metal has failed
Limitations
- Brittle at room temperature in the recrystallized condition, which limits forming and machining approaches
- Melting point too high for conventional casting, so all mill product goes through press and sinter
- Oxidizes rapidly above roughly 500 degrees Celsius in air, requiring vacuum or inert atmosphere at temperature
- Very difficult and expensive to machine, with heavy tool wear
- Cannot be conventionally welded with predictable results; joining generally requires brazing or mechanical methods
- Concentrated global supply with China dominant, and DoD sourcing restrictions on covered countries
- Expensive, and priced on a market with limited transparency
Governing specifications
| Designation | Body | Scope |
|---|---|---|
| ASTM B760 | ASTM International | Tungsten plate, sheet and foil |
| ASTM B777 | ASTM International | Tungsten base high density metal, covering the heavy alloy classes |
| MIL-T-21014 | U.S. Department of Defense | Tungsten base, high density metal |
| AWS A5.12 | American Welding Society | Tungsten and tungsten alloy electrodes for arc welding and cutting |
| 10 U.S.C. 4872 | United States Code | Prohibition on acquiring tungsten and tungsten alloys melted or produced in covered countries |