Refractories · Workhorse

Tungsten

Wvalues describe: sintered W

Fusion, privateBig science (accelerators, light sources, public fusion)Vacuum electronics & X-ray sourcesSemiconductor equipment & lithography

Why it wins

Highest melting point of any metal, low sputtering, low tritium retention. Since the 2023 rebaseline it is the ITER first wall armor, about 600 square meters, aligning ITER with every downstream reactor concept.

Why not the alternative

Beryllium, the original baseline, lost on toxicity, erosion dust, tritium co-deposition, and melting in disruptions. Cost of the swap: tungsten getters no oxygen, so boronization returns as an operations discipline, and core plasmas tolerate roughly 1000x less W than Be.

Watch out

Brittle below its ductile-brittle transition; cracks under thermal shock.

Properties

The values below are candidate: compiled from the sources named, not yet individually validated. Provisional provenance: Plansee refractory metal and alloy data; ITER and JET ITER-like wall programme; ASM Handbook: properties, corrosion, heat treatment.

Wet cleaning

Recipe	degrease, DI rinse; alkaline electrolytic clean or hydrogen fire to strip oxide
Forbidden	leaving it oxidised before a vacuum cycle: WO₃ is volatile
Limit	oxide removal, not particulate

Vacuum and outgassing

Outgassing, unbaked (10 h)	1e-9 mbar·L/s/cm²
Outgassing, baked	1e-12 mbar·L/s/cm²
Vapour pressure	negligible below 2500 °C

Temperature

Bake, assembled	450 °C
Vacuum degas	1500 °C
Braze / H2 firing	1800 °C
Metallurgical limit	recrystallises 1300–1400 °C

Thermal

CTE	4.5 ppm/K
Thermal conductivity	174 W/m·K
Specific heat	132 J/kg·K
Emissivity	0.05 polished RT, 0.35 at 2000 K
Melting / softening	3422 °C

Mechanical

Strength	750 ys MPa
Tensile	800–1500 MPa
Elongation	0–5 %
Young's modulus	411 GPa
Hardness	350–450 HV
Density	19.25 g/cm3

Electrical and magnetic

Relative permeability	~1.0
Resistivity	5.6 µΩ·cm

Engineering

Corrosion	inert in vacuum; oxidises above 400 °C in air
Joining	brazed; welding is specialist
Process notes	brittle at room temperature, ground rather than machined
Availability and cost	to order

Brazing

Sourced pairings

With	Filler	Atmosphere	Expansion gap at set
Nickel and nickel plating	Palco	not stated on the datasheet	expansion absent on both sides. Side A, 1219 °C is outside the range of nickel-200 (20 to 1000 °C), never extrapolated. Side B, 1219 °C is outside the range of tungsten (20 to 1000 °C), never extrapolated
CuCrZr (copper-chromium-zirconium)	Cu-TiH2-Ni	vacuum	set temperature absent: no solidus recorded for cu-tih2-ni
Oxygen-free copper C10100 / C10200	named only in prose: eutectic Au-Cu (and, per the review: Cu-Mn, Au-Cu-Fe, NiCuMn-37, Cu-22TiH2, amorphous Ti-Zr)	vacuum	no filler identified, nothing to derive
Oxygen-free copper C10100 / C10200 / CuCrZr (copper-chromium-zirconium)	named only in prose: none: OFE copper cast into the monoblock then HIP or HRP	HIP	no filler identified, nothing to derive

Preparation

copper interlayer
OFE copper interlayer

Compatibility

What documents state about this material faced with a filler metal, without the other member of the joint. A statement that names the exact filler comes first. A statement about a whole AWS class comes after it: a class covers dozens of alloys, so it is the weaker of the two, and the corpus never turns one into the other. Last come statements about a pair of base metals that name no filler at all. They are the weakest of the three, and they do not contradict the two above: a table that cannot generalize about a pair can still list a filler class for each metal of that pair separately. The three levels answer three different questions.

wetsNioro
Kohl states that this filler will wet tungsten and molybdenum as well as copper, Kovar, nickel and stainless steel, with excellent flow.
Conditions and source
Book page 192, table XVI, Brazing filler metals for high-vacuum systems. The table carries its own reserve, printed under it: adapted from the list of a commercial manufacturer, so it relays a manufacturer selection list and not a measurement by the author. The Applications column names base metals and never names the other member of the joint. Row 13 of the table, composition Ni 18 and Au 82, which matches the corpus entry Nioro BAu-4 exactly.
[A]W. H. Kohl, Soldering and brazing, Vacuum, volume 14, number 5, pages 175 to 198, 1964, Pergamon Press, PII 0042-207X(64)90858-9
Peer-reviewed review article on soldering and brazing for vacuum devices, republished later in the Handbook of Vacuum Physics edited by A. H. Beck. Table XVI, Brazing filler metals for high-vacuum systems, book page 192, lists 21 filler metals with liquidus, solidus and an Applications column. The table carries its own reserve, printed under it: adapted from the list of a commercial manufacturer. It is therefore a manufacturer selection list relayed by the author, not a measurement of his own, and the Applications column names base metals without naming a partner. The page of each statement is carried by the entry that uses it, never by this registry line.
wetsPalco
Kohl states that this filler has the lowest vapour pressure in its melting range and that it wets molybdenum and tungsten, for cathode structures.
Conditions and source
Book page 192, table XVI, Brazing filler metals for high-vacuum systems. The table carries its own reserve, printed under it: adapted from the list of a commercial manufacturer, so it relays a manufacturer selection list and not a measurement by the author. The Applications column names base metals and never names the other member of the joint. Row 4 of the table, composition Co 35 and Pd 65, which matches the corpus entry Pd 65 and Co 35 exactly.
[A]W. H. Kohl, Soldering and brazing, Vacuum, volume 14, number 5, pages 175 to 198, 1964, Pergamon Press, PII 0042-207X(64)90858-9
Peer-reviewed review article on soldering and brazing for vacuum devices, republished later in the Handbook of Vacuum Physics edited by A. H. Beck. Table XVI, Brazing filler metals for high-vacuum systems, book page 192, lists 21 filler metals with liquidus, solidus and an Applications column. The table carries its own reserve, printed under it: adapted from the list of a commercial manufacturer. It is therefore a manufacturer selection list relayed by the author, not a measurement of his own, and the Applications column names base metals without naming a partner. The page of each statement is carried by the entry that uses it, never by this registry line.
listedAWS class BAg
The AWS combination table lists the BAg class for brazing this base metal to Cu and Cu alloys, carbon and low-alloy steels, cast iron, stainless steel, Ni and Ni alloys, W, Mo, Ta, Nb and alloys, refractory metals, tool steels.
Conditions and source
Book page 75, chapter 3, table 3.2, Base Metal-Brazing Filler Metal Combinations. The cells that carry this class for this base metal name these partners: Cu and Cu alloys, carbon and low-alloy steels, cast iron, stainless steel, Ni and Ni alloys, W, Mo, Ta, Nb and alloys, refractory metals, tool steels. A partner is what the cell pairs the base metal with, it does not index this entry. The table lists classes, it does not qualify them, and an empty cell is never a prohibition. The class is written as the document writes it, BAl-Si becoming BAlSi here, and it is never mapped to any grade of the corpus. The table groups W, Mo, Ta, Nb and alloys as refractory metals. The document enumerates the four elements itself, so the corpus writes the cell under each of the four it carries.
[A]AWS Brazing Handbook, American Welding Society, chapter 3 Brazing Filler Metals and chapter 33 Electron Tubes and Vacuum Equipment
Handbook of the American Welding Society. Three tables are read by the corpus. Table 3.2 page 75, Base Metal-Brazing Filler Metal Combinations, a two-entry matrix of base metal families whose cells carry AWS filler classes. Table 3.3 page 76, Maximum Service Temperatures Recommended for Various Brazing Filler Metal Compositions, one continuous and one short-term temperature per class. Table 33.1 page 585, Composition of Brazing Filler Metals Specially Produced for the Brazing of Vacuum Devices and Equipment, with liquidus and solidus in Fahrenheit and Celsius. The chapter, the table and the page of each statement are carried by the entry that uses it, never by this registry line.
listedAWS class BAu
The AWS combination table lists the BAu class for brazing this base metal to carbon and low-alloy steels, cast iron, stainless steel, Ni and Ni alloys, W, Mo, Ta, Nb and alloys, refractory metals, tool steels.
Conditions and source
Book page 75, chapter 3, table 3.2, Base Metal-Brazing Filler Metal Combinations. The cells that carry this class for this base metal name these partners: carbon and low-alloy steels, cast iron, stainless steel, Ni and Ni alloys, W, Mo, Ta, Nb and alloys, refractory metals, tool steels. A partner is what the cell pairs the base metal with, it does not index this entry. The table lists classes, it does not qualify them, and an empty cell is never a prohibition. The class is written as the document writes it, BAl-Si becoming BAlSi here, and it is never mapped to any grade of the corpus. The table groups W, Mo, Ta, Nb and alloys as refractory metals. The document enumerates the four elements itself, so the corpus writes the cell under each of the four it carries.
[A]AWS Brazing Handbook, American Welding Society, chapter 3 Brazing Filler Metals and chapter 33 Electron Tubes and Vacuum Equipment
Handbook of the American Welding Society. Three tables are read by the corpus. Table 3.2 page 75, Base Metal-Brazing Filler Metal Combinations, a two-entry matrix of base metal families whose cells carry AWS filler classes. Table 3.3 page 76, Maximum Service Temperatures Recommended for Various Brazing Filler Metal Compositions, one continuous and one short-term temperature per class. Table 33.1 page 585, Composition of Brazing Filler Metals Specially Produced for the Brazing of Vacuum Devices and Equipment, with liquidus and solidus in Fahrenheit and Celsius. The chapter, the table and the page of each statement are carried by the entry that uses it, never by this registry line.
listedAWS class BCu
The AWS combination table lists the BCu class for brazing this base metal to carbon and low-alloy steels, cast iron, stainless steel, Ni and Ni alloys, W, Mo, Ta, Nb and alloys, refractory metals, tool steels.
Conditions and source
Book page 75, chapter 3, table 3.2, Base Metal-Brazing Filler Metal Combinations. The cells that carry this class for this base metal name these partners: carbon and low-alloy steels, cast iron, stainless steel, Ni and Ni alloys, W, Mo, Ta, Nb and alloys, refractory metals, tool steels. A partner is what the cell pairs the base metal with, it does not index this entry. The table lists classes, it does not qualify them, and an empty cell is never a prohibition. The class is written as the document writes it, BAl-Si becoming BAlSi here, and it is never mapped to any grade of the corpus. The table groups W, Mo, Ta, Nb and alloys as refractory metals. The document enumerates the four elements itself, so the corpus writes the cell under each of the four it carries.
[A]AWS Brazing Handbook, American Welding Society, chapter 3 Brazing Filler Metals and chapter 33 Electron Tubes and Vacuum Equipment
Handbook of the American Welding Society. Three tables are read by the corpus. Table 3.2 page 75, Base Metal-Brazing Filler Metal Combinations, a two-entry matrix of base metal families whose cells carry AWS filler classes. Table 3.3 page 76, Maximum Service Temperatures Recommended for Various Brazing Filler Metal Compositions, one continuous and one short-term temperature per class. Table 33.1 page 585, Composition of Brazing Filler Metals Specially Produced for the Brazing of Vacuum Devices and Equipment, with liquidus and solidus in Fahrenheit and Celsius. The chapter, the table and the page of each statement are carried by the entry that uses it, never by this registry line.
listedAWS class BNi
The AWS combination table lists the BNi class for brazing this base metal to carbon and low-alloy steels, cast iron, stainless steel, Ni and Ni alloys, W, Mo, Ta, Nb and alloys, refractory metals, tool steels.
Conditions and source
Book page 75, chapter 3, table 3.2, Base Metal-Brazing Filler Metal Combinations. The cells that carry this class for this base metal name these partners: carbon and low-alloy steels, cast iron, stainless steel, Ni and Ni alloys, W, Mo, Ta, Nb and alloys, refractory metals, tool steels. A partner is what the cell pairs the base metal with, it does not index this entry. The table lists classes, it does not qualify them, and an empty cell is never a prohibition. The class is written as the document writes it, BAl-Si becoming BAlSi here, and it is never mapped to any grade of the corpus. The table groups W, Mo, Ta, Nb and alloys as refractory metals. The document enumerates the four elements itself, so the corpus writes the cell under each of the four it carries.
[A]AWS Brazing Handbook, American Welding Society, chapter 3 Brazing Filler Metals and chapter 33 Electron Tubes and Vacuum Equipment
Handbook of the American Welding Society. Three tables are read by the corpus. Table 3.2 page 75, Base Metal-Brazing Filler Metal Combinations, a two-entry matrix of base metal families whose cells carry AWS filler classes. Table 3.3 page 76, Maximum Service Temperatures Recommended for Various Brazing Filler Metal Compositions, one continuous and one short-term temperature per class. Table 33.1 page 585, Composition of Brazing Filler Metals Specially Produced for the Brazing of Vacuum Devices and Equipment, with liquidus and solidus in Fahrenheit and Celsius. The chapter, the table and the page of each statement are carried by the entry that uses it, never by this registry line.

Against another base metal, no filler named:

not recommendedAl and Al Alloys
The AWS combination table does not recommend brazing this base metal to Al and Al Alloys.
Conditions and source
Book page 75, chapter 3, table 3.2, Base Metal-Brazing Filler Metal Combinations. The cell names no filler metal of any kind, neither a grade nor an AWS class. It states something about the combination of two base metals and nothing else. The document prints this reserve under the table and it is carried here in full: X means not recommended, however special techniques may be viable for certain dissimilar metal combinations. The document names this family W, Mo, Ta, Nb, and alloys refractory metals and enumerates its four metals itself, so the corpus writes the cell under each of the four it carries. The table names the family Al and Al Alloys, and the corpus carries 6061.
[A]AWS Brazing Handbook, American Welding Society, chapter 3 Brazing Filler Metals and chapter 33 Electron Tubes and Vacuum Equipment
Handbook of the American Welding Society. Three tables are read by the corpus. Table 3.2 page 75, Base Metal-Brazing Filler Metal Combinations, a two-entry matrix of base metal families whose cells carry AWS filler classes. Table 3.3 page 76, Maximum Service Temperatures Recommended for Various Brazing Filler Metal Compositions, one continuous and one short-term temperature per class. Table 33.1 page 585, Composition of Brazing Filler Metals Specially Produced for the Brazing of Vacuum Devices and Equipment, with liquidus and solidus in Fahrenheit and Celsius. The chapter, the table and the page of each statement are carried by the entry that uses it, never by this registry line.
no generalizationBe, Zr, V, and Alloys Reactive Metals
The AWS combination table states that no generalization can be made about brazing this base metal to Be, Zr, V, and Alloys Reactive Metals.
Conditions and source
Book page 75, chapter 3, table 3.2, Base Metal-Brazing Filler Metal Combinations. The cell names no filler metal of any kind, neither a grade nor an AWS class. It states something about the combination of two base metals and nothing else. The document prints this reserve under the table and it is carried here in full: Y means generalizations on these combinations cannot be made, refer to appropriate individual chapters for usable filler metals. The document names this family W, Mo, Ta, Nb, and alloys refractory metals and enumerates its four metals itself, so the corpus writes the cell under each of the four it carries. The document names this family Be, Zr, V, and alloys reactive metals and enumerates three metals of which the corpus carries only beryllium, so the entry names one member of a group the document treats together. The row label of the same family is printed without the comma after Zr.
[A]AWS Brazing Handbook, American Welding Society, chapter 3 Brazing Filler Metals and chapter 33 Electron Tubes and Vacuum Equipment
Handbook of the American Welding Society. Three tables are read by the corpus. Table 3.2 page 75, Base Metal-Brazing Filler Metal Combinations, a two-entry matrix of base metal families whose cells carry AWS filler classes. Table 3.3 page 76, Maximum Service Temperatures Recommended for Various Brazing Filler Metal Compositions, one continuous and one short-term temperature per class. Table 33.1 page 585, Composition of Brazing Filler Metals Specially Produced for the Brazing of Vacuum Devices and Equipment, with liquidus and solidus in Fahrenheit and Celsius. The chapter, the table and the page of each statement are carried by the entry that uses it, never by this registry line.
not recommendedMg and Mg Alloys
The AWS combination table does not recommend brazing this base metal to Mg and Mg Alloys.
Conditions and source
Book page 75, chapter 3, table 3.2, Base Metal-Brazing Filler Metal Combinations. The cell names no filler metal of any kind, neither a grade nor an AWS class. It states something about the combination of two base metals and nothing else. The document prints this reserve under the table and it is carried here in full: X means not recommended, however special techniques may be viable for certain dissimilar metal combinations. The document names this family W, Mo, Ta, Nb, and alloys refractory metals and enumerates its four metals itself, so the corpus writes the cell under each of the four it carries.
[A]AWS Brazing Handbook, American Welding Society, chapter 3 Brazing Filler Metals and chapter 33 Electron Tubes and Vacuum Equipment
Handbook of the American Welding Society. Three tables are read by the corpus. Table 3.2 page 75, Base Metal-Brazing Filler Metal Combinations, a two-entry matrix of base metal families whose cells carry AWS filler classes. Table 3.3 page 76, Maximum Service Temperatures Recommended for Various Brazing Filler Metal Compositions, one continuous and one short-term temperature per class. Table 33.1 page 585, Composition of Brazing Filler Metals Specially Produced for the Brazing of Vacuum Devices and Equipment, with liquidus and solidus in Fahrenheit and Celsius. The chapter, the table and the page of each statement are carried by the entry that uses it, never by this registry line.
no generalizationTi and Ti Alloys
The AWS combination table states that no generalization can be made about brazing this base metal to Ti and Ti Alloys.
Conditions and source
Book page 75, chapter 3, table 3.2, Base Metal-Brazing Filler Metal Combinations. The cell names no filler metal of any kind, neither a grade nor an AWS class. It states something about the combination of two base metals and nothing else. The document prints this reserve under the table and it is carried here in full: Y means generalizations on these combinations cannot be made, refer to appropriate individual chapters for usable filler metals. The document names this family W, Mo, Ta, Nb, and alloys refractory metals and enumerates its four metals itself, so the corpus writes the cell under each of the four it carries. The table names the family Ti and Ti Alloys, and the corpus carries CP grade 2.
[A]AWS Brazing Handbook, American Welding Society, chapter 3 Brazing Filler Metals and chapter 33 Electron Tubes and Vacuum Equipment
Handbook of the American Welding Society. Three tables are read by the corpus. Table 3.2 page 75, Base Metal-Brazing Filler Metal Combinations, a two-entry matrix of base metal families whose cells carry AWS filler classes. Table 3.3 page 76, Maximum Service Temperatures Recommended for Various Brazing Filler Metal Compositions, one continuous and one short-term temperature per class. Table 33.1 page 585, Composition of Brazing Filler Metals Specially Produced for the Brazing of Vacuum Devices and Equipment, with liquidus and solidus in Fahrenheit and Celsius. The chapter, the table and the page of each statement are carried by the entry that uses it, never by this registry line.

Open in the brazing abacus →

Outgassing

3 sourced measurements for this card. A rate means nothing without the pumping time it was read at, so each one states it or declares it missing. The whole base, filters included, is at /tools/outgassing/.

Signature: 1e-7 unbaked to 1e-13 baked, a drop of 6.0 decades.

Sourced outgassing measurements for this card
Material as published	Species	State	Pumping time	Rate
Tungsten	total	unbaked	NOT STATED by the source	2.60e-7mbar·L/s/cm²
Tungsten plates	total	baked	NOT STATED by the source	less than2.70e-13mbar·L/s/cm²
Tungsten plates	total	baked	NOT STATED by the source	3.30e-11mbar·L/s/cm²

Sources: S-LIGO-E960050-V13, S-CERN-THESIS-2019-061. Full citations and conditions at the base and in /data/outgassing.json.

Grades

Pure W (99.97 plus)	PFC armor plates and X-ray targets
ITER-grade forged W	controlled texture and grain for monoblocks
WL10 (W-1 La2O3)	machinable, creep resistant: electrodes, furnace parts
K-doped W (AKS wire)	non-sag filaments and heaters
W-5Re / W-26Re	focal track alloys and C-type thermocouples