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TUNGSTEN TECHNICAL DATA
(This information downloaded
from www.hightempmetals.com) |
Description
Tungsten has the highest melting point
and the best high temperature strength of the four common refractory
metals. Tungsten has been used for many years in the lamp industry
for filaments. It has gained wide acceptance as an essential material
in electrical contacts, glass-to-metal seals, support and electrodes.
The demand for tungsten is increasing because the growing technology
in electronics, nucleonics, and aerospace demands increased materials
performance and reliability at higher and higher temperatures.
Fabricability of tungsten is no longer the critical problem that
it was a few years ago. Engineered reproducible tungsten products
coupled with newly developed tools and techniques have minimized
or eliminated fabrication problems.
Application
Tungsten is used because of its: exceptional
strength and stiffness at high temperatures, good thermal conductivity,
low thermal expansion and emissivity in many electronic applications;
strength, stiffness, thermal expansion, low vapor pressure, electrical
resistivity, emissivity, ductility, and fabricability in high temperature
furnace applications; strength, erosion resistance, corrosion resistance,
resistance to thermal shock, and fabricability for nozzle and other
hardware in aerospace application; resistance to thermal shock and
erosion in die casting applications.
Chemical Behavior of Tungsten
| CORROSIVE |
BEHAVIOUR |
| Hydrochloric
acid, sulphuric
acid or nitric acid ..........
Acqua Regia ..................
Hydrofluoric acid ...........
Hydrofluoric and nitric acid
mixed ........................
Alkalies ....................
Amonia .......................
Sodium nitrite ...............
Carbon (lampblack, graphite)
(charcoal) and hydrocarbons ...
Sulfur .......................
Mercury and mercury vapor ...
Aluminum oxide, magnesium
oxide ........................
Thorium oxide ................
Air and oxygen .................
Water ........................
Water vapour .................
Hydrogen .....................
Nitrogen .....................
Ammonia ......................
Carbon monoxide ..............
Carbon dioxide ...............
Halogens .....................
Hydrogen chloride gas ........
Nitric oxide .................
Hydrogen sulphide ............
Sulfur dioxide ...............
Carbon disulphide ............
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Cold, dilute
or concentrated: practically insoluble
Warm dilute or concentrated: slight attack
Cold: pratically insoluble.
Warm: rapide attack
Cold or warm: insoluble
Rapid attack
Cold aqueousl caustic soda or potash: practically
insoluble. Molten caustic soda or potash or
alkaline carbonates:
a) in air: slow oxidation
b) in the presence of oxiding agents, e.g.
KNO3 KNO2 KCLO3
PBO2: rapid solution.
Pratically insoluble to attack by aqueous solution;
slight attack in the presence of H2O2
Molten: rapid solution above 300°C(570°F)
Formation of carbides from 1400°c(2550°F)complete
carburization to WC at 1400° to 1600° (2550° to
2900°F)
Molten or boiling: slow attack
Pratically insoluble.
Reduction to metal in contact with tungsten above
1900°C(3450°F)
Reduction to metal in contact with tungsten above
2200°C(4000°F)
Insoluble at room temperature; oxidation starts from
400 to 500°C(750 to 930°F); at temperature above
this rapid oxidation to WO3 and vaporization.
Insoluble at all temperatures.
At red heat rapid oxidation to WO3
No reaction up to melting point.
No reaction up to highest temperature.
Slight formation of nitrides with powder from 700°C
(1290°F). Nitrides disassociate above this temperature.
Carburation begins at 800°C(1470°F)
Oxidation above 1200°C(2190°F)
Fluorine: attack at normal temperatures.
Chlorine: attack at 250°C(480°F)
Bromine and iodine: attack at light red heat
Up to 600°C(1110°F) no attack if free of oxygen
oxidation to WO3 at high temperatures
Surface attack at red heat
Oxidation at high temperatures
Attack at red heat.
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Physical Properties
| Property |
Test Condition |
Value |
Units |
| Atomic Number |
-- |
74 |
-- |
| Atomic Weight |
-- |
183.92 |
-- |
| Density |
-- |
19.3
0.70 |
gm/cu cm
lbs/in |
| Melting
Point |
-- |
3410
6170 |
°C
°F |
| Boiling
Point |
-- |
5900
10652 |
°C
°F |
| Vapor Pressure |
2000°C (3630°F)
3000°C (5430°F) |
5 x 10(-9)
1 x 10(-3) |
Torr
Torr |
| Evaporation
Rate |
1530°C (2790°F)
1730°C (3150°F)
1930°C (3500°F)
2130°C (3870°F)
2330°C (4230°F)
2530°C (4590°F) |
1.3 x 10(-10)
5.3 x 10(-8)
7.5 x 10(-6)
4.6 x 10(-4)
1.4 x 10(-2)
2.7 x 10(-1) |
mg/cm² hour |
| Linear Coefficient
of Thermal
Expansion |
20°C (68°F)
1000°C (1830°F)
2000°C (3630°F) |
4.43 x 10(-6)
5.17 x 10(-6)
7.24 x 10(-6) |
°C (-1) |
| Specific
Heat |
20°C (68°F)
1000°C (1830°F)
2000°C (3630°F) |
3.3 x 10(-2)
4.1 x 10(-2)
4.7 x 10(-2) |
Cal/gm-°C |
| Thermal
Conductivity |
20°C (68°F)
1000°C (1830°F)
2000°C (3630°F) |
0.31
0.27
0.25 |
Cal/cm-sec-°C |
| Specific
Electrical
Resistance |
20°C (68°F)
1000°C (1830°F)
2000°C (3630°F)
3000°C (5430°F) |
5.5
33
66
103 |
Microhm-cm |
| Rate of
Electron Emission |
1600°C (2910°F)
1900°C (3450°F)
2200°C (3990°F) |
0.1
10
250 |
ma/cm² |
| Thermal
Neutron cross
section |
-- |
19.2 |
barns |
| Wave length
of
characteristic
X-Rays |
L-series
K-series |
0.21
1.48 |
Å |
| Total Intensity
of radiation |
1000°C (1830°F)
2000°C (3630°F)
3000°C (5430°F) |
2.5
47
240 |
W/cm² |
| Intensity
of
illumination |
2000°C (3630°F)
3000°C (5430°F) |
100
750 |
Candles/cm² |
Mechanical Properties
As the temperature increases, these
mechanical properties drop in value, as is expected. What is unusual
is that at very high temperetures, wrought tungsten still has usuable
design strength. At 3600°F, tungsten sheet still have a strength
of 3000 psi. That is high when one considers that at that temperature
most metals are a liquid.
The biggest problem with tungsten is that it is a difficult metal
to fabricate. For example, take a piece of as-rolled, .060" thick
tungsten sheet, and try to bend it 90° at room temperature. It will
break. Anneal the as-rolled sheet above its recrystallization temperature
(about 2400°F), and try to bend it 90° at room temperature. Again
it will break. However, heat the as-rolled sheet to 1500°F, and
it can be bent 90°. But heat the annealed sheet (recrystallized)
to 1500°F, and it will break when bent 90°.
This means that wrought tungsten should be fabricated somewhere
above its "brittle-to-ductile" transition temperature and below
its recrystallization temperature. This condition can be most easily
understood by an explanation of how wrought tungsten is made.
| Property |
Test Condition |
Value |
Units |
| Modulus
of
Elasticity |
68°F
1830°F |
58
52 |
psi x 10(6)
psi x 10(6) |
| Hardness |
Slightly
worked
wire & sheet over
.040"
Severely worked
wire & sheet under
.040"
Recrystallized |
300-500
500-750
360
|
DPH
DPH
DPH
|
| Tensile
Strength |
Slightly
worked
wire & sheet over
.040"
Severely worked
wire & sheet under
0.40"
Recrystallized |
140-250
200-780
140-170
|
psi x 10(3)
psi x 10(3)
psi x 10(3)
|
| Transition |
Brittle-Ductile |
400-950 |
°F |
Mechanical & Physical Properties of the Densimet Alloys
In those applications where tungsten
because of its specific gravity, is used to generate high inertial
forces, the requirement for high temperature strength is not present.
In these applications, the designer usually wants tungsten in a
form that provides high density along with good machining properties
and sometimes room-temperature ductility. To meet these requirements,
a series of tungsten alloys known as DENSIMET have been developed.
Rather than beigh wrought, these alloys are made of tungsten powder,
pressed & sintered with a nickel-iron or nickel-copper binder
to achieve the desired combination of properties. The strength of
these alloys is dependent upon the binder. Hence, they do not possess
the high temperature properties of wrought tungsten. They are, however,
very useful alloys for the applications for which they were designed,
and should always be considered. The properties of three of these
alloys are shown in the table below.
Alloyed Tungsten In Its Wrought
Form
Tungsten-25% Rhenium: One of the inherent problems with unalloyed
tungsten is its lack of ductility (brittleness) at room temperature.
The addition of 25 % rhenium gives rise to an alloy that has both
desirable high temperature strength and useful room temperature
properties. Furthermore, these properties are present in both the
stress-relieved and recrystallized conditions.
If the application requires tungsten with ductility after operating
above recrystallization temperature, the tungsten-25% rhenium alloy
may be a logical choice. It might also be selected if the fabrication
of the part is unusually difficult and if, for some reason , heating
during fabrication is not possible. Unlike unalloyed tungsten, weldments%
made in tungsten-25% rhenium are ductile (weldments made in unalloyed
tungsten always recrystallized the metal and hence are brittle).
The primary drawback to the use of rhenium is its cost which at
$800 to $1500 per pound makes the tungsten-25% rhenium alloy very
expensive.
Tungsten- Thoria: The tungsten-thoria
composition is used in the wire form in lamp applications where
hot strength and electron emission properties, better than that
available from unalloyed tungsten, are required. Thoriated tungsten
rod is used for TIG welding electrodes because of its better arc
stability. Since thoriated tungsten is easier to machine than unalloyed
tungsten, its 2% composition is sometimes substituded for unalloyed
tungsten as a means of reducing cost.
| Property |
HD 17
90% W
*6% Ni
4% Cu |
HD 17D
90% W
7% Ni
3% Fe |
HD 17.5
92.5% W
5.25% Ni
2.25% Fe |
HD 18
95% W
3.5% Ni
1.55% Cu |
HD 18D
95% W
3.5% Ni
1.5% Fe |
HD 18.5
97% W
2.1% Ni
.9% Fe |
| Mil, Spec.
T-21014D
SAE Aero. Material Spec.
(AMS) 7725B
ASTM-B-777-87 |
Class 1
7725B
Class 1 |
Class 1
7725B
Class 1 |
Class 2
--
Class 2 |
Class 3
--
Class 3 |
Class 3
--
Class 3 |
Class 4
--
Class 4 |
| Density
Gms/cc
Density Lbs/cu.in |
17
.614 |
17
.614 |
17.5
.632 |
18
.650 |
18
.650 |
18.5
.668 |
| Hardness
Rockwell C |
24 |
25 |
26 |
27 |
27 |
28 |
| Ultimate
Tensile
Strength (psi) |
110,000 |
120,000 |
114,000 |
110,000 |
120,000 |
123,000 |
| Yield Strength
.2% offset (psi) |
80,000 |
88,000 |
84,000 |
85,000 |
90,000 |
85,000 |
| Elongation
(% in 1") |
6 |
10 |
7 |
7 |
7 |
5 |
| Proportion
Elastic
Limit (psi) |
45,000 |
52,000 |
46,000 |
45,000 |
44,000 |
45,000 |
| Modulus
of
Elasticity (psi) |
40 x 10(6) |
45 x 10(6) |
47 x 10(6) |
45 x 10(6) |
50 x 10(6) |
53 x 10(6) |
| Coefficient
of Thermal
Expansion
x 10(-6)/°C (20-400°C) |
5.4 |
4.61 |
4.62 |
4.43 |
4.6 |
4.5 |
| Thermal
Conductivity
(CGS Units) |
.23 |
.18 |
.20 |
.33 |
.26 |
.30 |
| Electrical
Conductivity
(% IACS) |
14 |
10 |
13 |
16 |
13 |
17 |
| Magnetic
Properties |
NIL |
Slightly
Magnetic |
Slightly
Magnetic |
NIL |
Slightly
Magnetic |
Slightly
Magnetic |
Properties may vary according
to size and shape of part
*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.
Tungsten's Reaction at Elelevated Temperature
Because of its high temperature strength,
tungsten is used in a number of application where the temperature
is as high as 4500°F. Unfortunately, tungsten is not an inert metal,
and reacts with certain gases and other materials unless adequate
precautions are observed. A familiarity with these high temperature
reactions help the designer avoid some of the more obvious pitfalls.
Air...Above 950°F tungsten reacts with the oxygen in ari
forming a volatile oxide coating on the surface. This is a surface
reaction which, while causing wastage of the tungsten, does it no
internal strutural harm. Above 2200°F, there is a strong evaporation
of the oxide formation. Obviously tungsten should not be used in
air above 950°F except for very short duration.
Hydrogen, Nitrogen, Ammonia and Inert Gases...For all practical
purposes, tungsten is stable with all these gases up to its melting
point. Some surface nitriding has been reported above 2700°F.
Water Vapor...Tungsten can tolerate water vapor at all temperatures
providing the dew point does not exceed -15°F. Between dew points
of -15 and 70°F, tungsten can be used up to approximately 2500°F.
Carbon Dioxide & Monoxide...Above 2500°F, carbon dioxide
oxidizes tungsten. Above 1450°F, carbon monoxide reacts with tungsten
to form its carbide.
Carbon & Hydrocarbons...Tungsten react with graphite
and other carbonaceous forms above 2550°F to form tungsten carbide.
Vacuum...In a vacuum of 10(-2) Torr, tungsten is stable in
that it does not react with the residual gases up to 3650°F Torr.
Strong evaporation occurs above 4350°F.
Ceramic Oxides...Tungsten has excellent resistance to attack
by the metallic oxides.
Molten Metals...Tungsten exhibits good resistance to attack
from many molten metals including mercury, gallium, sodium, potassium,
NAK, magnesium, bismuth and zinc. Tungsten is attacked by molten
aluminum, however, the rate of attack is much less than with other
metals.
Workability
Because of its high hardness and low
ductility the following recommendation for the working of tungsten
should be noted. In comparision with molybdenum it is far more difficult
to work both by machining and by other methods not involving metal
removal. The range of shapes that can be produced is thus correspondingly
restricted.
Forming
Sharp tools are required for cutting tungsten sheet and the sheet
itself must be at a temperature between 750 and 1800°F according
to its thickness. Rods are cut with thin organically bonded silicon
carbide wheels, water cooled (peripheral speed about 13 ft. per
second). Sheet can be bent at 1500 to 1800°F.
Disc can be blanked out of sheet using sharp tools, and since thick
sheet must be preheated to about 1800°F high alloyed high temperature
steel or, better, hard metal must be used for the tools. Thicker
sheet up to .200" with an appreciable circumfernce can be shaped
by stamping at a high temperature. Deep drawing is generally speaking
impossible. Thicker rod can only be bent at a red heat. Electrolytically
polished rod up to .12" diameter can, however, be bent cold to a
certain extent.
Machining
Tungsten machines with short chips. Because of its high hardness
only hard metal tools (grade H2) can be used for turning, milling
and drilling. The top rake should be 20 to 25" and the clearance
5 to 8".
Cutting conditions are as followed:
Speed: 6 to 14 ft/min
Feed: .0004 to .0006"
Depth of Cut: .02 to .04"
Shaped tungsten pieces are mostly produced in quantity of grinding.
Silicon carbide wheels of hardness J to L, grain size 100 to 120
are used with a speed of 11 to 13 ft/sec with continuous water cooling.
Attaching Tunsten to other materials
Tungsten cannot be folded or riveted. It can, however, be upset
to a certain extent at high temperatures. It can be welded, but
brazing is preferable in most cases.
Hope this information will be helpful for you to design the product,
for more information, please be free to contact us.
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