Tungsten is number 74 on the periodic table, in between tantalum and rhenium. Tungsten has the highest melting point (3410°C) of the four common refractory metals. In addition, with a density of 19.3 gm/ cc, it is only surpassed by rhenium and osmium in weight.

Tungsten has a long history of use for filaments in the lamp industry. It offers exceptionally high strength at very high temperatures. In fact, it has the best hightemperature strength of the four common refractory metals. Its high-temperature strength, combined with its good electrical resistivity, have made it a popular choice for other applications in addition to filaments.

It is used for heating elements in vacuum furnaces that exceed the temperatures of molybdenum and tantalum as well as other heater applications. Tungsten has also gained wide acceptance as an essential material in electrical contacts, glass-to-metal seals, supports, and electrodes.

Tungsten's properties lend themselves to other metals when alloyed. Tungsten carbide has long been the choice for durable cutting tools. Tungsten's high density is used in conjunction with copper, nickel, iron, and cobalt to form heavy metal. This is an alloy containing 90%-97% tungsten and the other metals are used as a binder to keep the tungsten together and to give it machinable properties as well as to temper the brittleness of pure tungsten. Heavy metal is widely used for counter balances, radio isotope containers, and armor penetrations. Refer to "Heavy Metals".

Tungsten has the best high-temperature strength of all the refractory metals. For this reason, it is used in very high temperature vacuum furnaces, i.e., those that operate at 2000'C and above. It is also widely used in arc lamps for both the cathode and anode. Its coefficient of expansion makes it a good material to choose in making hermetic glass-to-metal seals. Its stiffness at elevated temperatures makes it excellent for high-temperature support components in lamps.

Tungsten is very difficult to machine and fabricate. With experience, it can be turned. Milling is all but impossible. It is only done with great difficulty and high cost by those most experienced with it. Forming must be done at very high temperatures and with careful stress relieving. Welding is not recommended and riveting is difficult at best. Extreme care must be exercised when designing a component from tungsten. Rembar will readily provide assistance during the design stage upon request. Rembar offers tungsten in powder, sheet, wire, rod, and pressed/ sintered forms. If it is possible to fabricate the part needed from tungsten, Rembar can do it for you.

There is an increasing demand from the electronics, nuclear, and aerospace industries for materials that maintain reliability under ever-increasing temperature conditions. Because its properties meet these requirements, tungsten also is experiencing an increasing demand.

Characteristics that support the demand for tungsten in many electronics applications are its:

• strength and stiffness at high temperatures
• good thermal conductivity
• low thermal expansion
• low emissivity

Tungsten is also relied upon in high temperature furnace applications because of its properties that provide:

• strength and stiffness
• thermal expansion
• low vapor pressure
• electrical resistivity
• emissivity
• productivity and fabricability

Tungsten has a coefficient of expansion approximating that of hard glass. For this reason, it is used extensively in glass-to-metal seals in hard glass lamp and electronic applications. Under special conditions, it may also be used with quartz.

All rod intended for sealing purposes is processed and inspected to produce split-free material with no surface imperfections.

Since tungsten rod has a high degree of strength at elevated temperatures, it is utilized structurally to hold or support high temperature sources such as filaments and heaters for lamp and electronic uses.

Tungsten rod that is specially processed and manufactured for welding rod applications is used extensively in such processes as inert-gas-shielded arc welding and atomic hydrogen arc welding.

Other types of tungsten rod are used for electrodes. These types, both regular and thoriated, are used for electrodes in vacuum melting processes, resistance welding, and electro-discharge machining.

The resistance welding of most refractory metals and their alloys is not normally done for several reasons :

• The resulting cast, coarse grained microstructure has essentially no ductility or toughness.
• The coefficients of thermal expansion are much lower than most common metals, that results in cracking upon cooling if dissimilar metals are joined. 
• The Refractory Metals are also chemically reactive and will oxidize unless heated in inert gas or vacuum. Some Electron Beam Welding is perform to join these metals for low stress applications.

For tube applications, especially flash and xenon tubes, tungsten is used either as pure or thoriated at 1% and 2% for greater emissivity.

Because of Tungsten's high hardness and low ductility, it is a difficult material to fabricate. The best method for machining that involves metal removal is E.D.M. For parts such as tubes, crucibles and other small, thin-walled items, C.VD. is an effective, but costly, method of achieving them. There are times when neither of these methods will suffice and then conventional methods must be used.

A cleaning process is designed to deal with one or more of the following:

• surface scale
• general contamination
• removal of a basis metal

Of all the potential contaminants in wrought products, iron is of primary concern. Others, such as aluminum, carbon, calcium, copper, nickel, etc., may also be present as elements, but they are more frequently present in the form of oxides.

Removal of a controlled amount of basis metal may be desired to insure complete removal of contaminants.

There are four main processes used to clean tungsten:

Molten Salt

This is one of the most common cleaning processes, requiring simple immersion in a molten bath containing oxidizing agents. This process will not attack the basis metal.

Aqueous Alkaline Solutions

This process works well on oxidized (yellow tungsten) surfaces. Reduced or intermediate oxides (brown, purple, etc.) will react more slowly to this process, if at all.

A tightly adherent black scale, with or without carbon, is commonly found on tungsten that has been worked at high temperature. Despite the fact that it is predominantly W03, normally yellow in bulk, it is only slowly attacked even by a hot, concentrated solution. This is probably due more to its dense, fused, physical state than because of its chemical nature.

This process is similar to the use of molten salts in that it will not attack the basis metal and it requires an oxidizing agent to work.

Add Solutions

Tungsten is much less reactive to individual acids than most common metals. HCI, HF, and H₂SO₄ have essentially no effect. When tungsten is treated with acid solutions, it frequently is stained by residual oxides even if rapid and thorough rinsing is used.

Electrolytic Methods

Electrolytic etching is the removal of basis metal by an applied voltage in a medium capable of dissolving the products of the electrolytic reaction. This may be done in molten salts or aqueous solutions. Electrical current and time determine the amount of metal removal.

There are five primary cleaning methods for cleaning tungsten:

• Immerse the material in a 20% solution of potassium hydroxide that has been brought to a boil.
• Etch the material in a 20% solution of potassium hydroxide.
• Etch the material in a 50 vol. % HN0₃ - 50 vol. % HF solution.
• Immerse in molten sodium hydroxide.
• Immerse in molten sodium hydride.

For rapid attack of heavy scale, molten salt is far superior to the other methods. In addition, if no oxidizer is present, it can be performed with no fear of basis metal loss.

If appreciable sizes or volumes of material are to be processed, particularly with significant basis metal removal, acid solutions present a disposal, as well as an operational, problem.

The utility of electro-etching is more dependent on geometry than the other methods. It will work well for treating continuous lengths of wire, however there is a contact problem if the cleaning is to be performed on many small parts.

For all systems involving basis metal attack, rate control must be achieved by definition of concentration, temperature, and time of exposure.

Porous Tungsten

Porous Tungsten is a new product that can replace wrought tungsten for many applications. It has similar characteristics but yields less strength because it has a sintered structure rather than a worked structure. The starting powder is compacted, then sintered in a hydrogen atmosphere at high temperatures. Because of the high sintering temperature, this material can be used for applications requiring the material to see temperatures as high as 2000°C without ill effect. For applications requiring higher temperatures the material can be processed to accommodate. The starting powders are 99.9% pure tungsten and because of the strict processing controls we have in place the billets are also of high purity. The density of these billets can vary from 80 –90 % dense depending on the requirements of the application. For further details or to discuss your application please contact Rembar.

Our manufacturing process also lends itself to the compaction and sintering of large billets. Billets can also be made close to finish size reducing costs by reducing waste material and cutting times. Often times a billet can be made large enough to make parts that would normally have to be made from two or more pieces and somehow held together. This can reduce assembly times and costs. With the sizes available, parts can now be manufactured where tungsten has been restricted to available sizes.

Heavy Metal is made possible by P/M techniques. This is a technique where tungsten powder is mixed with nickel, iron or copper powder. It is then compacted and liquid phase sintered. The result is a very high-density machinable material having a homogeneous structure with no grain direction. This provides a material with unique physical properties and applications.

Because of the physical properties of heavy metal, it is often used as both a weight and structural member. Weights and counterbalances for aircraft control surfaces and rotor blades, guidance platforms, balancing of flywheels and crankshafts, vibration damping governors, and fuse masses and weights for self-winding watches are typical applications. Other specific applications include:

Because of the absorption characteristics of heavy metals, approximately one-third less material is required as compared to lead.

Heavy metal is used for source shielding on oil wells and industrial instrumentation as well as for collimators and shielding in medical therapy and detection equipment.

Due to the material's unique combination of physical properties and high density, it can be rotated at extremely high speeds.

This aspect makes it ideal for use in gyroscope rotors, flywheels, and rotating members for governors.

Properties such as elongation and hardness make heavy metal advantageous for use in kinetic energy penetrators. These properties can also be varied by manufacturing technique and additives.

Heavy metal is used in squares, spheres, and projectile shapes for hypervelocity armor penetrating applications.

Heavy metal is used for "chatter-free" boring and grinding. It is used where rigidity and minimum vibration are desirable. Heavier cuts and a better finish can be achieved with tools made of heavy metal. Longer tool extensions, with ratios up to 9:1 are also possible depending on the diameter of the tool.

Other benefits include:

• Longer tool life due to the lower amount of heat generated as a result of the minimum chatter and high thermal conductivity that heavy metal provides.
• Heavy metals do not anneal during brazing, therefore carbide can be brazed directly with no effect on the shank. This allows continued use.
• Higher accuracy and trouble-free grinding are achieved when used as grinding quills. This is due to the vibration damping effect and rotating inertia characteristics of heavy metals.

  Heavy metal is often used in place of Tungsten Carbide boring bars because:

• they have a higher density
• they are readily machinable
• they are less prone to chipping and breakage
• lower cost is achieved both with material and finishing

Material *	17 gm/cc 90% W 6% Ni 4% Cu	17 gm/cc 90% W 6% Ni 4% Cu/Fe	17 gm/cc 90% W 7% Ni 3% Fe	17.5 gm/cc 92.5% W 5.25% Ni 2.25% Fe	18 gm/cc 95% W 3.5% Ni 1.5% Cu	18 gm/cc 95% W 3.5% Ni 1.5 Fe	18.5 gm/cc 97% W 2.1% Ni 0.9% Fe
Density; lbs/in3	0.614		0.614	0.632	0.65	0.65	0.668
Mil. Spec. T-21014 D	Class 1		Class 1	Class 2	Class 3	Class 3	Class 4
ASTM-B-459-67	Grade 1 Type II & III		Grade 1 Type II & III	Grade 2 Type II & III	Grade 3 Type II & III	Grade 3 Type II & III	Grade 4 Type II & III
Hardness; Rockwell C	24		25	26	27	27	28
Ultimate Tensile Strength; PSI	110,000		125,000	114,000	115,000	125,000	128,000
Yield Strength, .2% Offset; PSI	90,000		88,000	90,000	85,000	90,000	85,000
Elongation, % in 1"	8		14	12	7	12	10
Proportional Elastic Limit; PSI	45,000		52,000	46,000	45,000	44,000	45,000
Modulus of Elasticity; PSI	40 x 106		45 x 106	47 x 106	45 x 106	50 x 106	53 x 106
Coefficient of Thermal Expansion (x 10-6 1°C 20°-400°C)	5.4		4.8	4.6	4.4	4.6	4.5
Thermal Conductivity; CGS Units	0.23		0.18	0.20	0.33	0.26	0.30
Electrical Conductivity; %IACS	14		10	13	16	13	17
Magnetic Properties	NIL	Slightly Magnetic	Slightly Magnetic	Slightly Magnetic	NIL	Slightly Magnetic	Slightly Magnetic

* Composition shown is typical and may change for manufacturing purposes or to meet physical and/or application requirements. If non-magnetic material is required, it should be specified.

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