Niobium and Niobium Alloys
Niobium is the light refractory metal: 8.57 g/cm³, barely more than steel, with a 2,477 °C melting point and a modulus of 105 GPa. Annealed pure niobium yields only 100–150 MPa and stretches 30 % or more, so it forms and welds like a soft copper, and it is a superconductor below 9.2 K. C-103 (Nb-10Hf-1Ti) yields about 300 MPa at room temperature and keeps useful strength to 1,370 °C, which is why silicide-coated C-103 is the standard material for radiatively cooled rocket-thruster skirts. Like every refractory metal it oxidizes above about 400 °C in air and picks up hydrogen if pickled carelessly.
Popular niobium grades
Compare in the explorer| Grade | Yield, MPa | Tensile, MPa | Density, g/cm³ | Machinability | Weldability | Best for |
|---|---|---|---|---|---|---|
| Pure Nb | 125 | 220 | 8.57 | Poor | Very good | Superconducting cavities, vacuum parts, implants |
| C-103 | 275 | 415 | 8.85 | Poor | Very good | Thruster nozzles and skirts to 1,370 °C |
| R04261 | 200 | 310 | 8.57 | Poor | Excellent | Nb-1Zr for alkali metals and lamp feedthroughs |
| Cb-752 | 310 | 450 | 9.03 | Poor | Very good | Stronger nozzle and leading-edge alloy |
| C-129Y | 480 | 585 | 9.46 | Poor | Very good | Higher-strength formable thruster alloy |
| FS-85 | 480 | 585 | 10.6 | Poor | Very good | Highest creep strength in the group |
| NbTi | 350 | 620 | 6.05 | Poor | Fair | Superconducting magnet wire |
Choose niobium for
Rocket and satellite thruster nozzles, skirts and combustion chambers that are radiatively cooled (C-103, Cb-752, C-129Y, FS-85); superconducting RF cavities and magnet wire (Pure Nb, NbTi); sodium- and lithium-cooled reactor and heat-pipe components and lamp feedthroughs (Nb-1Zr); vacuum and getter hardware; and hypoallergenic implant and jewelry parts that anodize to color.
Look elsewhere when
The part runs hot in air without a coating (a nickel or cobalt superalloy such as L605 or Inconel 625), the environment is a hot concentrated acid where Pure Ta or Ta-2.5W resist and niobium merely survives, load-bearing strength above 1,400 °C is needed (TZM, Ta-10W or Pure W), or the job is a general vacuum-furnace fixture that Pure Mo does at lower cost with far better creep strength.
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Niobium by application
- Thruster nozzles and hot structure
- C-103 sheet formed, TIG- or electron-beam welded and silicide-coated for nozzle extensions and chambers; Cb-752, C-129Y and FS-85 where the metal temperature or the load is higher than C-103 tolerates.
- Superconducting and vacuum hardware
- Pure Nb of RRR grade for RF cavities, R04210 for vacuum and getter parts and sputter targets, NbTi wire in a copper matrix for MRI and accelerator magnets.
Working with niobium
- Machining
- Soft and gummy like tantalum: very sharp positive tools, high speed, light feeds, flood coolant and chlorinated oil for drilling and tapping to prevent galling. C-103 and FS-85 cut more like a work-hardening stainless. Deburr carefully — the metal smears rather than chips.
- Forming and welding
- Pure Nb and C-103 sheet deep-draw, spin and bend to a tight radius at room temperature and weld by TIG or electron beam with full inert coverage on both sides; any air contact leaves a brittle, discolored joint. Anneal in high vacuum at 1,000–1,200 °C.
- Coatings and finishing
- Silicide coatings (R512E and similar) protect C-103 and its siblings in hot exhaust for the duration of a mission; bare niobium stays in vacuum or inert gas above 400 °C. Anodizing gives durable interference colors on jewelry and implant markers; electropolishing and buffered chemical polishing prepare superconducting cavities.
Other refractory metal series
Niobium and Niobium Alloys — frequently asked
What is niobium?
Niobium is the light refractory metal: 8.57 g/cm³, barely more than steel, with a 2,477 °C melting point and a modulus of 105 GPa. Annealed pure niobium yields only 100–150 MPa and stretches 30 % or more, so it forms and welds like a soft copper, and it is a superconductor below 9.2 K. C-103 (Nb-10Hf-1Ti) yields about 300 MPa at room temperature and keeps useful strength to 1,370 °C, which is why silicide-coated C-103 is the standard material for radiatively cooled rocket-thruster skirts. Like every refractory metal it oxidizes above about 400 °C in air and picks up hydrogen if pickled carelessly.
Which grade of niobium should I use?
Pure Nb for superconducting RF cavities, vacuum and getter hardware, sputter targets, implant components and anodized jewelry — R04210 is the commercial-purity grade for those, and N1 the national-standard equivalent. R04251 and R04261 are Nb-1Zr, reactor and commercial grade: better creep strength than pure niobium and the standard for liquid-alkali-metal systems and high-pressure sodium lamp feedthroughs. C-103 for thruster nozzles, extensions and hot structure that must be formed, welded and then run at 1,200–1,370 °C under a coating. C-129Y and Cb-752 give more strength at temperature than C-103 with somewhat less formability; FS-85 is the strongest and most creep-resistant of the group, at a density of 10.6 g/cm³. NbTi is the superconducting wire alloy in MRI and accelerator magnets.
Which grade of niobium is the strongest?
C-129Y has the highest yield strength in the series at 480 MPa; FS-85 follows at 480 MPa. Values are for each grade's default condition.
Which grade of niobium is easiest to machine?
R04261 (machinability poor, 33/100), then N1 (32/100).
Why is C-103 the rocket-nozzle alloy?
It is the best compromise the industry found: light (8.85 g/cm³), ductile enough to spin and weld into thin-wall bells, strong enough at 1,200–1,370 °C for a radiatively cooled skirt, and coatable with a silicide that survives the oxidizing exhaust. Cb-752 and C-129Y are stronger but harder to form; FS-85 is stronger still but 20 % heavier. C-103 has flown on every generation of satellite and lunar-module thrusters since the 1960s, which counts for a great deal in a qualified design.
Niobium or tantalum?
Chemically cousins, but tantalum is twice the density and resists hot concentrated acids where niobium only resists the milder ones — so tantalum for acid equipment. Niobium for anything where weight, price or superconductivity matters: thruster skirts, RF cavities, magnet wire, jewelry and implant parts. Both anodize to color, both weld only under total inert coverage, and both embrittle from hydrogen if pickled without care.