Cast supealoyCobalt based alloyPrecision alloySUPER ALLOY
Refractory metal
Titanium & Zirconium alloy
Sputtering taget
Niobium (Nb)-Rare Refractory Metal
1. Product Overview
Niobium is a lustrous grayish-white transition metal that is extremely stable in air at room temperature, does not react with air, and is not completely oxidized even when red-hot in oxygen. High-purity niobium has excellent ductility and can be cold worked into plate, strip, foil, bar, wire, tube, and many other forms, with cold-rolling reductions of more than 80% without intermediate annealing; however, it becomes markedly harder and more brittle as the content of impurities (especially oxygen, nitrogen, hydrogen, and carbon) increases.
Niobium (element symbol Nb, atomic number 41) is a silver-gray, soft, and highly ductile rare refractory metal with a melting point of 2468 °C and a density of only 8.57 g/cm³ — the lowest density among refractory metals. It combines three key advantages: excellent resistance to acid and alkali corrosion (a cost-effective substitute for tantalum), the highest superconducting critical temperature among the elements (9.2 K), and a very low thermal neutron absorption cross section (1.15 barns).
Niobium is extremely stable in air at room temperature, does not react with air, and is not completely oxidized even when red-hot in oxygen. High-purity niobium has excellent ductility and can be cold worked into plate, strip, foil, bar, wire, tube, and many other forms, with cold-rolling reductions of more than 80% without intermediate annealing; however, it becomes markedly harder and more brittle as the content of impurities (especially oxygen, nitrogen, hydrogen, and carbon) increases.
Three key decision points in selection are: purity grade and RRR value (the core indicator for superconducting applications), alloy system (pure niobium, Nb-1Zr, C-103, Nb521, and NbTi have completely different uses), and supply form and tolerance class. Chemical corrosion protection and coating applications focus on purity and surface quality, while superconducting applications must specify the RRR value and upper limits for gas elements.
Our niobium and niobium alloy products cover plate, strip and foil, bar, wire, tube, sputtering targets, crucibles, and parts machined to drawing. They can be produced and accepted in accordance with GB/T 3630, GB/T 14842, ASTM B392 / B393 / B394, or a technical agreement between both parties, and are supplied together with chemical composition analysis reports and material certificates.
2. Chemical Composition
Typical chemical composition requirements for pure niobium (wt%, balance Nb)
Element | Nb1 (GB) | Nb2 (GB) | Superconducting grade (high-purity RRR) |
Nb content | ≥99.95% | ≥99.9% | ≥99.99% (4N or higher) |
Ta | ≤0.1% | ≤0.15% | ≤0.05% (tightened per agreement) |
O | ≤0.03% | ≤0.05% | ≤0.005%–0.01% |
N | ≤0.01% | ≤0.02% | ≤0.005% |
C | ≤0.02% | ≤0.03% | ≤0.003%–0.01% |
H | ≤0.002% | ≤0.005% | ≤0.0005%–0.002% |
Fe, Si, Ni, Ti, W, Mo, etc. | each ≤0.005%–0.02% | each ≤0.01%–0.05% | Strictly controlled per agreement |
Note: The table above summarizes values from common commercial specifications; specific limits are subject to the edition of the applicable standard and the technical agreement. The upper limits for interstitial elements (O, N, C, H) in superconducting-grade niobium are far stricter than in industrial grade, which is also why it is significantly more expensive. |
3. Key Performance Parameters
The three core data sets for niobium — physical properties, mechanical properties, and chemical composition — correspond respectively to thermal and electrical design, structural strength verification, and the basis for purchasing acceptance. Note in particular that superconducting applications have far stricter requirements on interstitial elements than industrial grade; the relevant data are listed separately for comparison.
(1) Physical properties
Typical physical properties of niobium (room temperature, reference values)
Item | Typical value | Item | Typical value |
Element symbol / atomic number | Nb / 41 | Density (20 °C) | 8.57 g/cm³ |
Atomic weight | 92.906 | Melting point | 2468 °C |
CAS number | 7440-03-1 | Boiling point | 4742 °C |
Crystal structure | Body-centered cubic (bcc) | Thermal conductivity | ≈53.7 W/(m·K) |
Electrical resistivity (20 °C) | ≈12.5 µΩ·cm | Coefficient of thermal expansion | ≈7.3×10⁻⁶ /K |
Specific heat capacity | ≈0.265 J/(g·K) | Elastic modulus | ≈105 GPa |
Poisson's ratio | ≈0.40 | Thermal neutron absorption cross section | ≈1.15 barns |
Superconducting critical temperature Tc | 9.2 K | Appearance | Silver-gray metallic luster |
Note: The table above lists typical values compiled from public sources; these values vary with purity, processing state, and test temperature. Some sources record the melting point of niobium as 2477 °C, which is due to differences in testing and purity. Formal acceptance is subject to the material certificate (MTC) supplied with the goods and the technical agreement between both parties. |
(2) Mechanical properties
Table 3-2 Mechanical properties of niobium and typical niobium alloys (annealed, typical value ranges)
Material | Tensile strength | Yield strength | Elongation | High-temperature behavior |
Pure niobium (Nb1 / Nb2, annealed) | 195–275 MPa | 100–205 MPa | ≥25% | Good ductility; suitable for deep drawing and spinning |
Nb-1Zr (NbZr1) | 275–380 MPa | 170–275 MPa | ≥20% | About 50% higher strength than pure niobium, with better creep resistance |
Nb521 (Nb-5W-2Mo-1Zr) | ≥440 MPa | ≥320 MPa | ≥20% | Retains relatively high strength at 1200 °C |
C-103 (Nb-10Hf-1Ti) | ≥480 MPa | ≥380 MPa | ≥20% | Can serve long-term in environments of about 1200 °C |
Annealed pure niobium has modest strength but excellent ductility and is a typical "easy to form, hard to hold dimensions" material: deep-drawing and spinning performance are excellent, but finished parts have relatively low stiffness, so excessively thin load-bearing structures should be avoided in design. Where high-temperature strength is required, alloy systems such as Nb-1Zr, Nb521, or C-103 should be selected.
4. Grades, Standards, and Alloy Systems
Common standards and grade equivalents for niobium
Standard | Scope | Typical grades | Remarks |
GB/T 3630 | Niobium and niobium alloy plate, strip, and foil | Nb1, Nb2, NbZr1 | The most commonly used Chinese standard for plate; purity ≥99.9%–99.95% |
GB/T 14842 | Niobium and niobium alloy bar | Nb1, Nb2, NbZr1 | Forged, rolled, or drawn condition |
GB/T 8183 | Niobium and niobium alloy seamless tube | Nb1, Nb2 | Tubing for chemical heat exchangers and nuclear applications |
ASTM B392 | Niobium and niobium alloy bar and wire | R04200, R04210, R04251, R04261 | US standard bar and wire system |
ASTM B393 | Niobium and niobium alloy strip, sheet, and plate | R04200, R04210, R04251, R04261, R04220 | R04220 is superconducting-grade high-purity niobium |
ASTM B394 | Niobium and niobium alloy seamless and welded tube | Same pure niobium grades as above | Tubing system |
Main alloy systems and typical applications
Alloy | Composition characteristics | Reason for selection | Typical applications |
Pure niobium | Nb ≥99.9% | Corrosion resistant, easy to form, superconducting | Chemical linings, sputtering targets, superconducting cavities, electronic components |
Nb-1Zr | Nb + 1% Zr | Better strength and creep resistance than pure niobium, while retaining good ductility | Sodium vapor lamps, nuclear industry components, chemical equipment |
Nb-47Ti / Nb-50Ti | Nb + 47%–50% Ti | Mature low-temperature superconducting wire | MRI magnets, NMR, accelerator dipole magnets |
Nb₃Sn | Niobium-tin intermetallic compound | Higher critical field than NbTi | ITER fusion magnets, high-field NMR, accelerator quadrupole magnets |
C-103 | Nb-10Hf-1Ti | 1200 °C-class high-temperature strength and oxidation resistance | Rocket nozzle extensions, thrust chambers, high-temperature structural parts |
Nb521 | Nb-5W-2Mo-1Zr | Mature Chinese aerospace high-temperature niobium alloy | Aerospace high-temperature structural parts, thermal protection components |
Ferroniobium FeNb | 63%–67% Nb, balance Fe | Grain refinement and precipitation strengthening | HSLA steel, pipeline steel (the largest application of niobium) |
Selection note: pure niobium and niobium alloys cannot be compared side by side by "purity level". For superconducting cavities, the RRR value and the upper limits for interstitial elements must be specified; for high-temperature structural parts, C-103 or Nb521 should be selected directly; for chemical corrosion protection, pure niobium or Nb-1Zr is preferred. With different applications, the grade systems are completely different. |
5. Available Forms and Size Ranges
Available forms and size ranges (actual availability subject to order confirmation)
Form | Common size range | Delivery condition | Reference standard |
Niobium plate | Thickness 0.5–20 mm, width 50–600 mm, length ≤2000 mm | Hot rolled, cold rolled, annealed, ground | GB/T 3630, ASTM B393 |
Niobium strip / foil | Thickness 0.01–0.8 mm, width 10–600 mm | Cold rolled, annealed, bright finish | GB/T 3630, ASTM B393 |
Niobium bar | φ3–100 mm, length cut to order | Forged, rolled, ground, annealed | GB/T 14842, ASTM B392 |
Niobium wire | φ0.1–6.0 mm | Cold drawn, annealed | ASTM B392 |
Niobium tube | OD 6–80 mm, wall thickness 0.5–5 mm | Seamless, welded, annealed | GB/T 8183, ASTM B394 |
Niobium sputtering target | Round targets φ50–400 mm; rectangular targets per drawing; backing plate bonding available | Machined, polished, clean-room packaged | Technical agreement |
Niobium crucible / profiled parts | Customized to drawing | Spinning, stamping, welding, machining | Per drawing |
Niobium powder / niobium pentoxide | Particle size per mesh or D50 as agreed, purity 3N–4N | Atomization, reduction, or chemical method | Technical agreement |
Thickness tolerance is typically ±0.01 mm, and can reach ±0.005 mm for high-end coating and superconducting applications. Slight oxidation colors are permitted on the surface of strip and foil and do not affect service performance; however, a severe oxide layer (typically more than 5 µm thick) must be removed by pickling before delivery or further processing.
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