How is Tungsten Alloys made of?
What's Tungsten Alloys
We are dedicated to the manufacture of tungsten alloy materials satisfying the most stringent requirements of manufacturing industries. Three tungsten alloys are produced commercially: tungsten-ThO2, tungsten-molybdenum, and tungsten-rhenium. The W-ThO2, alloy contains a dispersed second phase of 1 to 2% thorium. The thorium dispersion enhances thermionic electron emission, which in turn improves the starting characteristics of gas tungsten arc welding electrodes. It also increases the efficiency of electron discharge tubes and imparts creep strength to wire at temperatures above one-half the absolute melting point of tungsten.
Tungsten mill products, sheet, bar, and wire are all produced via powder metallurgy. These products are available in either commercially pure (undoped) tungsten or commercially doped (AKS-doped) tungsten. These additives improve the recrystallization and creep properties of tungsten, which are especially important when tungsten is used for incandescent lamp filaments. Wrought P/M stock can be zone refined by EB melting to produce single crystals that are higher in purity than the commercially pure product. Electron beam zone-melted tungsten single crystals are of commercial interest for applications requiring single crystals with very high electrical resistance ratios.
Tungsten Heavy-Metal Alloys (WHAs).
These are a category of tungsten-base materials that typically contain 90 to 98 wt% W. Most commercial WHAs are two-phase structures, the principal phase being nearly pure tungsten in association with a binder phase containing the transition metals plus dissolved tungsten. As a consequence, WHAs derive their fundamental properties from those of the principal tungsten phase, which provides for both high density and high elastic stiffness. It is these two properties that give rise to must applications for this family of materials.
The current uses of WHAs are spanning a wide range of consumer, industrial, and government applications that include:
- Damping weights for computer disk drive heads
- Balancing weights for ailerons in commercial aircraft, helicopter rotors, and for guided missiles
- Kinetic energy penetrators for defeating heavy armor
- Fragmentation warheads
- Radiation shielding, radio isotope containers, and collimalion apertures for cancer therapy devices
- High performance lead-free shot for waterfowl hunting
- Gyroscope components
- Weight distribution adjustment in sailboats and race cars.
Many applications that require high gravimetric density for balance weights, inertial masses, or kinetic energy penetrators or high radiographic density for radiation shielding and collimaiion necessitate rather large bulk shapes. Such a requirement eliminates all but a few candidates on the basis of prohibitive cost, typically reducing the choice of very dense alloys down to either tungsten- or uranium-base materials.
Uranium alloys, like lead, are eliminated from an increasing number of potential applications based on toxicity considerations, with uranium-base materials requiring a license except for very small quantities. While the precious metals listed possess attractive densities and offer essentially no toxicity, their cost is prohibitive for all but a few density applications.
WHAs typically consist of 90 to 98 wt% W in combination with some mix of nickel, iron, copper, and/or cobalt. The bulk of WHA production falls into the 90 to 95% W range.
The choice of alloy composition is driven by several considerations. The primary factor is the density required by the given application. Further considerations include corrosion resistance, magnetic character, mechanical properties, and postsinter heat treatment options.
The first WHA developed was a W-Ni-Cu alloy. Alloys of this ternary system are still occasionally used today, primarily for applications in which ferromagnetic character and electrical properties must be minimized. W-Ni-Cu alloys otherwise offer inferior corrosion resistance and lower mechanical properties than the present industry standard W-Ni-Fe alloys.
The majority of current uses for WHAs are best satisfied with the W-Ni-Fe system. Alloys such as 93W-4.9Ni-2.lFe and 95W-4Ni-lFe represent common compositions. The addition of cobalt to a W-Ni-Fe alloy is a common approach for slight enhancement of both strength and ductility. The presence of cobalt within the alloy provides solid-solution strengthening of the binder and slightly enhanced tungsten-matrix interfacial strength. Cobalt additions of 5 to 15% of the nominal binder weight fraction arc most common.
For extremely demanding applications, even higher mechanical properties are obtainable from the W-Ni-Co system with nickel-to-cobalt ratios ranging from 2 to 9. Such alloys require resolution/quench, however, due to extensive intermetallic (Co3W and others) formation on cool down from sintering.
A number of special WHAs are known as well. An example is the W-Mo-Ni-Fe quaternary alloy, which utilizes molybdenum to restrict tungsten dissolution and spheroid growth, resulting in higher strengths (but reduced ductility) in the as-sintered slate.
There are also a number of alloy systems in various stages of development for kinetic energy penetrators that are intended to provide a WHA that will undergo high deformation rate failure by shear localization in a manner similar to quenched and aged U-0.75Ti for more efficient armor defeat. These alloys to date have not exhibited a property set of interest for industrial applications, however.
How to make Tungsten Heavy Alloys?
Here after is the typical processing method which is working in ChinaTungsten Online's Workshop:
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