Refractories · Workhorse

Tantalum

Tavalues describe: pure Ta

Vacuum electronics & X-ray sourcesBig science (accelerators, light sources, public fusion)Quantum hardwareSemiconductor equipment & lithography

Why it wins

The forgiving refractory: ductile, weldable, chemically stubborn. Crucibles and evaporation boats, heaters, noble-diode ion pump cathodes, and since 2021 the qubit film that tripled transmon coherence on sapphire.

Why not the alternative

Tungsten is stiffer but brittle and unweldable in practice; molybdenum embrittles at welds. Ta pays its price tag back in fabricability.

Watch out

Drinks hydrogen above 300 C: embrittles if heated in poor vacuum.

Properties

The values below are candidate: compiled from the sources named, not yet individually validated. Provisional provenance: Plansee refractory metal and alloy data; ASM Handbook: properties, corrosion, heat treatment; Kurt J. Lesker materials notes.

Wet cleaning

Recipedegrease and DI rinse; nitric-HF etch where the surface matters, as in transmon work
Forbiddenhydrogen furnaces: it absorbs H and embrittles
Limitsurface oxide quality, which is what the qubit work is chasing

Vacuum and outgassing

Outgassing, unbaked (10 h)1e-9 mbar·L/s/cm²
Outgassing, baked1e-12 mbar·L/s/cm²
Vapour pressurenegligible below 2200 °C

Temperature

Bake, assembled450 °C
Vacuum degas1600 °C
Braze / H2 firing2000 °C
Metallurgical limitrecrystallises ~1100 °C

Thermal

CTE6.5 ppm/K
Thermal conductivity57 W/m·K
Specific heat140 J/kg·K
Emissivity0.1
Melting / softening3017 °C

Mechanical

Strength165–200 ys MPa
Tensile200–300 MPa
Elongation25–40 %
Young's modulus186 GPa
Hardness90–120 HV
Density16.65 g/cm3

Electrical and magnetic

Relative permeability~1.0
Resistivity13.5 µΩ·cm

Engineering

Corrosionimmune to almost everything below 150 °C
JoiningEB welds beautifully
Process notesthe transmon platform metal since 2021, for its stable oxide
Availability and costexpensive, to order

Brazing

Sourced pairings

WithFillerAtmosphereExpansion gap at set
Nickel and nickel platingPalconot stated on the datasheetexpansion 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 tantalum (20 to 1000 °C), never extrapolated

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.

  • 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.

Chemical affinity

What documents state about a BINARY SYSTEM, one element of a filler metal faced with one element of this material. An affinity is not a verdict on a joint: a joint brings many binaries together at once, some helpful and some harmful, and what follows is the list of those the corpus can name. The count below is not written anywhere. It falls out of the crossing of this material's elements with the composition of every filler the corpus holds, so it grows on its own the day a binary enters the corpus.

Elements of this material: Ta, the material is the element.

brittle intermetallic6 fillersAu against Ta1 source+1 statement

The two elements combine into a compound that is harder and less tolerant of strain than either of them. It sits in the filler, in the base next to the interface, or in both.

Gold between 40 and 90 percent tends to form brittle age-hardening compounds when brazing tantalum. Below 40 percent gold the same copper-gold family is used without that reservation.Au against Ta

6 fillers: 35Au-62Cu-2Ti-1Ni, 35Au/65Cu, BAu-1, Indalloy 182, Nicoro-80, Nioro

Conditions and verbatim

Book page 99, section on tantalum and its alloys. The chapter states that copper-gold alloys having less than 40 percent Au can also be used as filler metals, but that gold in amounts between 40 and 90 percent tends to form brittle, age-hardening compounds. The condition is a WINDOW on the gold content OF THE FILLER, not a temperature, which is why this entry carries no characteristic temperature. Of the four gold-bearing fillers this corpus holds, BAu-1 at 37.5 percent sits below the window and the three others, Nioro at 82, Nicoro-80 at 81.5 and Indalloy 182 at 80, sit inside it. The abacus serves the entry and its window and lets the reader read the filler composition it already displays.

Source[A] M. M. Schwartz, Brazing, 2nd edition, ASM International, 2003, chapter 4, Base Metals and Base-Metal Family Groups, DOI 10.1361/brse2003p063

Source conditionsChapter 4 of the second edition, book pages 63 to 162 in the copy read, which treats base metals family by family and states metallurgical reactions, atmosphere limits and filler selection guides. It is a handbook chapter, not a qualification record. The page of each statement is carried by the entry that uses it, never by this registry line.

Open in the brazing abacus →

Grades

R05200 (pure Ta)crucibles, heaters, liners
R05252 (Ta-2.5W)strength at temperature
Sputtered alpha-Ta filmtransmon qubit electrodes on sapphire
Sources · 2
  1. Place et al., tantalum transmon platform, 2021
  2. Kurt Lesker materials notes

Used by

Tools

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