spore: profile
id: vanadium-niobium
spore_version: 0.2
family: refractory-metals
name: Vanadium alloys (V-4Cr-4Ti, V-Ti, V-Nb)
abbreviation: V alloys
role: fusion first-wall and blanket structural alloys, and vanadium-based hydrogen-permeation membranes
category: metals
type: refractory-metals
summary: |
  The reference vanadium alloy for fusion is V-4Cr-4Ti, a vanadium base with about 4 percent chromium and 4 percent titanium by weight. Argonne reports high ductility, with about 20 percent uniform elongation. A property compilation gives a room-temperature yield strength of about 402 MPa, calculated here from its published correlation. After neutron irradiation to 28 to 46 dpa at 400 to 600 C, uniform elongation stayed above 8 percent. In air and oxygen at 500 to 700 C the alloy forms a surface oxide, and in Pint and DiStefano's tests the oxide did not prevent embrittlement. Vanadium-titanium-nickel and vanadium-niobium-titanium alloys are being studied as hydrogen-permeation membranes. A Savannah River test found a V-Ti-Ni membrane with a higher hydrogen permeation rate than palladium at 22 C, but the sources read here give no tensile data for the binary V-Ti or V-Nb alloys.
best_for: Fusion first-wall and blanket structures that must carry load at high temperature with low activation (Argonne)
weakest_at: 'Oxygen and hydrogen pickup: the alloy embrittles after exposure to oxygen at 500 to 700 C, and vanadium-based membranes are highly susceptible to hydrogen embrittlement'
identity:
  formula: 'V-4Cr-4Ti: vanadium with nominal 4 wt.% Cr and 4 wt.% Ti (Argonne Table 1 heats: BL-47 4.1Cr-4.3Ti, 832665 3.8Cr-3.9Ti, T87 4.9Cr-5.1Ti, BL-63 4.6Cr-5.1Ti, in wt.%; trace nitrogen 28 to 220 wppm). V-Ti-Ni membrane tested by SRS: 53 wt.% V, 26 wt.% Ti, 21 wt.% Ni. V-Nb-Ti-Co: quaternary, composition not stated in the page used.'
  source: unt-smith-1996
  where: Section 2 and Table 1, Compositions of Vanadium Base Alloys (nominal composition, wt.%)
tags:
  environments: []
  stresses: []
  applications:
    - structures
    - propulsion-and-tanks
properties:
  - benchmark: density
    label: Density, V-4Cr-4Ti at room temperature
    value: 6.05
    unit: g/cm3
    scope: material
    conditions:
      grade: V-4Cr-4Ti
      temperature: room temperature (RT), as printed
      unit_in_source: 6.05x10 3 kg/m3 (the page's unit; entered as 6.05 g/cm3, the same value)
    method: Value printed in the RT Density row of a property compilation for V-4Cr-4Ti (courtesy of Mike Billone), citing the ITER Materials Properties Handbook. Printed as 6.05x10 3 kg/m3; entered in g/cm3 with the same number
    status: ground
    source: qedfusion-v4cr4ti
    where: Property table, RT Density row
  - benchmark: melting_point
    label: Melting point, V-4Cr-4Ti
    value: 1900
    unit: °C
    scope: material
    conditions:
      grade: V-4Cr-4Ti
      tolerance: plus or minus 25 C as printed
    method: Value printed in the property compilation for V-4Cr-4Ti, citing the ITER Materials Properties Handbook
    status: ground
    source: qedfusion-v4cr4ti
    where: Property table, Melting temp. row
  - benchmark: elastic_modulus
    label: Young's modulus, V-4Cr-4Ti at 20 C
    value: 125.6
    unit: GPa
    scope: material
    conditions:
      grade: V-4Cr-4Ti
      temperature: 20 C
      correlation: printed as 125.6 times (1 minus 7.69 x 10-5 times (T minus 20)), valid RT to 1627 C
    method: Calculated by Space Mushroom from the printed correlation at 20 C, where the temperature term is 1.00 and the value equals the prefactor
    status: calculated
    source: qedfusion-v4cr4ti
    where: Property table, Young's modulus row
  - benchmark: yield_strength
    label: Yield strength, V-4Cr-4Ti at 20 C (from correlation)
    value: 402
    unit: MPa
    scope: material
    conditions:
      grade: V-4Cr-4Ti
      temperature: 20 C
      basis: printed correlation Sy = 402 times a temperature polynomial that equals 1.00 at 20 C, valid RT to 700 C
      temper: not stated in the compilation
    method: Calculated by Space Mushroom from the printed correlation evaluated at 20 C; the compilation says the correlation is fitted from several references
    status: calculated
    source: qedfusion-v4cr4ti
    where: Property table, Yield Strength row (see also its Fig. 2)
  - benchmark: design_yield_strength
    label: Design yield strength, V-4Cr-4Ti at 20 C (from correlation)
    value: 322
    unit: MPa
    scope: material
    conditions:
      grade: V-4Cr-4Ti
      temperature: 20 C
      basis: printed design correlation Syd = 322 times the same polynomial, equal to 1.00 at 20 C
    method: Calculated by Space Mushroom from the printed design correlation evaluated at 20 C
    status: calculated
    source: qedfusion-v4cr4ti
    where: Property table, Design Yield Strength row
  - benchmark: ultimate_tensile_strength
    label: Ultimate tensile strength, V-4Cr-4Ti at 20 C (from correlation)
    value: 488
    unit: MPa
    scope: material
    conditions:
      grade: V-4Cr-4Ti
      temperature: 20 C
      basis: printed correlation Su = 488 times a temperature polynomial that equals 1.00 at 20 C, valid RT to 700 C
    method: Calculated by Space Mushroom from the printed correlation evaluated at 20 C
    status: calculated
    source: qedfusion-v4cr4ti
    where: Property table, Ultimate Tensile Strength row (see also its Fig. 1)
  - benchmark: design_ultimate_tensile_strength
    label: Design ultimate tensile strength, V-4Cr-4Ti at 20 C (from correlation)
    value: 424
    unit: MPa
    scope: material
    conditions:
      grade: V-4Cr-4Ti
      temperature: 20 C
      basis: printed design correlation Sud = 424 times the same polynomial, equal to 1.00 at 20 C
    method: Calculated by Space Mushroom from the printed design correlation evaluated at 20 C
    status: calculated
    source: qedfusion-v4cr4ti
    where: Property table, Ultimate Design Tensile Strength row
  - benchmark: elongation
    label: Total elongation, V-4Cr-4Ti at 20 C (from correlation)
    value: 30.8
    unit: '%'
    scope: material
    conditions:
      grade: V-4Cr-4Ti
      temperature: 20 C
      basis: printed correlation et = 30.8 times a temperature polynomial that equals 1.00 at 20 C
    method: Calculated by Space Mushroom from the printed correlation evaluated at 20 C
    status: calculated
    source: qedfusion-v4cr4ti
    where: Property table, Total elongation row (see also its Fig. 4)
  - benchmark: uniform_elongation
    label: Uniform elongation, V-4Cr-4Ti, unirradiated
    value: 20
    unit: '%'
    scope: material
    conditions:
      grade: V-4Cr-4Ti (BL-47 and production heat 832665), unirradiated
      temperature: room temperature to 700 C
      basis: about 20 percent, printed as -20 percent; the text calls this high ductility
    method: Value stated in the tensile section of the Argonne reference-alloy paper
    status: ground
    source: unt-smith-1996
    where: Section 4, Tensile Properties
  - benchmark: uniform_elongation
    label: Uniform elongation, V-4Cr-4Ti after neutron irradiation
    value: 8
    bound: lower
    unit: '%'
    scope: material
    conditions:
      grade: V-4Cr-4Ti
      irradiation: 28 to 46 dpa at 400 to 600 C in fast reactors
      test: at the irradiation temperature and at room temperature after irradiation at 420 to 600 C
    method: Value stated in the irradiation section of the Argonne reference-alloy paper; the paper says greater than 8 percent
    status: ground
    source: unt-smith-1996
    where: Section 6, Irradiation Effects, text on Fig. 10
  - benchmark: reduction_in_area
    label: Reduction in area, V-4Cr-4Ti at 600 C and below
    value: 70
    bound: lower
    unit: '%'
    scope: material
    conditions:
      grade: V-4Cr-4Ti and V-5Cr-5Ti heats in the paper
      temperature: 600 C and below
      basis: greater than 70 percent as printed
    method: Value stated in the tensile section of the Argonne reference-alloy paper
    status: ground
    source: unt-smith-1996
    where: Section 4, Tensile Properties, text on Fig. 7
  - benchmark: ductile_brittle_transition_temperature
    label: Ductile-to-brittle transition temperature, Charpy, unirradiated
    value: -200
    bound: upper
    unit: °C
    scope: material
    conditions:
      grade: two V-4Cr-4Ti heats (BL-47 and production heat 832665) and one V-5Cr-5Ti heat (T87)
      treatment: thermal-mechanical treatments including 1 h anneals at 950 to 1125 C
      method: Charpy one-third-size specimens
    method: Value stated in the impact section; the paper says the DBTT is below -200 C for all three heats
    status: ground
    source: unt-smith-1996
    where: Section 3, Impact Properties, and Figure 1
corrosion:
  - environment: Air and oxygen at 500 to 700 C, uncoated V-4Cr-4Ti
    headline: In air and oxygen at 500 to 700 C, V-4Cr-4Ti forms a surface oxide and then embrittles, even when the oxide is present.
    effect: Pint and DiStefano exposed V-4Cr-4Ti to air, oxygen and low-pressure oxygen at 500 to 700 C. Linear oxidation kinetics were measured up to 2000 hr at low oxygen pressure. At higher pressures, oxygen uptake and an external oxide layer followed linear-parabolic kinetics. Tensile ductility at 25 and 600 C was reduced. Specimens with an external oxide were embrittled severely after a further 2000 hr anneal at 700 C, and the authors conclude that a surface oxide will not prevent degradation.
    rating: severe
    conditions:
      exposure: 500 to 700 C, air or oxygen at 105 Pa and low oxygen pressure, up to 2000 hr
      alloy: V-4Cr-4Ti
      tests: tensile tests at 25 and 600 C after exposure
    source: pint-distefano-2005
    where: Abstract
  - environment: Liquid lithium, as a coolant or breeder in fusion blankets
    headline: The reference-alloy paper calls V-4Cr-4Ti compatible with lithium.
    effect: The Argonne paper lists good compatibility with lithium among the reasons vanadium-base alloys are candidates for fusion first-wall and blanket structures. It gives no corrosion rate, exposure time or temperature for that statement, so treat it as a qualitative finding.
    rating: low
    conditions:
      basis: general statement in the introduction of the reference-alloy paper, with no test conditions given
      alloy: V-4Cr-4Ti and related V-Cr-Ti alloys
    source: unt-smith-1996
    where: Section 1, Introduction
risks:
  hazards:
    - text: Vanadium powder, sold by Stanford Advanced Materials, is classified as a flammable solid (H228), causes skin and eye irritation (H315, H319) and may cause respiratory irritation (H335). Its signal word is Danger. The classification applies to the powder, not to a bulk alloy part.
      ghs:
        - H228
        - H315
        - H319
        - H335
      source: sds-vanadium-powder
      where: Section 2, Hazards Identification (GHS labelling)
    - text: PubChem records that vanadium does not meet GHS hazard criteria in 95.4 percent (431 of 452) of company reports, and that 21 of 452 reports give hazard codes. The codes are not printed in the record extract read here.
      ghs: []
      source: pubchem-vanadium
      where: GHS Classification section, aggregated ECHA C and L notifications
  failure_risks:
    - mode: Oxygen embrittlement of V-4Cr-4Ti in air or oxygen
      trigger: Exposure to air or oxygen at 500 to 700 C, followed in the test by a further anneal at 700 C
      consequence: Pint and DiStefano measured reduced tensile ductility after exposure, and severe embrittlement after a 2000 hr anneal at 700 C of specimens that had formed an external oxide.
      severity: high
      source: pint-distefano-2005
      where: Abstract
    - mode: Hydrogen embrittlement of a vanadium-based membrane alloy
      trigger: Hydrogen absorbed into a vanadium-based alloy, for example during hydrogen permeation
      consequence: The Qingdao paper says larger hydrogen absorption weakens mechanical strength. Substituting niobium for vanadium in V-Nb-Ti-Co alloys shifted the ductile-to-brittle transition hydrogen concentration about 0.36 H/M to the right.
      severity: high
      source: qust-vnbti-co
      where: Abstract
  side_effects: []
  handling:
    - text: 'Keep the powder in a cool, dry place in tightly closed containers, with adequate ventilation, and away from oxidizing agents. Do not use water on a fire: the SDS calls for a special powder for metal fires.'
      source: sds-vanadium-powder
      where: Sections 5 and 7 (storage, extinguishing media)
  mitigations:
    - text: The Argonne paper reports little effect of anneal temperature on impact properties when V-4Cr-4Ti is annealed in a high-vacuum system.
      source: unt-smith-1996
      where: Section 3, Impact Properties
uses:
  - application: structures
    device: Fusion reactor first-wall and blanket structures
    example: Argonne describes vanadium-base alloys as promising candidates for fusion reactor first-wall and blanket structures because of low irradiation-induced activity, good mechanical properties, good compatibility with lithium and high thermal conductivity.
    source: unt-smith-1996
    where: Section 1, Introduction
  - application: propulsion-and-tanks
    device: Hydrogen separation membrane (purifier for hydrogen feed gas)
    example: Savannah River tested an arc-melted V53-Ti26-Ni21 membrane, which had a steady-state hydrogen permeation rate an order of magnitude higher than pure palladium at 22 C. The report describes applications such as front-end purifiers for fuel-cell systems. This is the closest allowed application value for a hydrogen separation membrane; it is a laboratory result, not a flight use.
    source: srs-vtin
    where: Abstract, Results and Discussion, Table 1
supply:
  - subject: Vanadium (mine production, 2025 estimate)
    producers:
      - country: China
        share_percent: 74.5
        year: 2025
      - country: Russia
        share_percent: 19.1
        year: 2025
      - country: Brazil
        share_percent: 4.8
        year: 2025
      - country: South Africa
        share_percent: 4.5
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (vanadium included)
        listed: true
      - list: EU critical raw materials list (vanadium included)
        listed: true
    recycling: 'USGS: recycling of vanadium is mainly reprocessing of vanadium catalysts into new catalysts.'
    substitutes:
      - 'USGS: manganese, molybdenum, niobium, titanium and tungsten are to some degree interchangeable with vanadium in steel. No acceptable substitute for vanadium is available for use in aerospace titanium alloys.'
    source: usgs-mcs2026-vanadium
    where: World Mine Production and Reserves table, 2025e (China 82,000 t, Russia 21,000 t, Brazil 5,300 t, South Africa 5,000 t; world total 110,000 thousand t, rounded). Shares calculated by Space Mushroom against that total; Recycling and Substitutes paragraphs.
documents:
  - title: 'USGS Mineral Commodity Summaries 2026: Vanadium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-vanadium.pdf
    year: 2026
  - title: Safety data sheet, spherical vanadium powder (CAS 7440-62-2), Stanford Advanced Materials
    type: sds
    url: https://samaterials.com/tds/1697121437-spherical-vanadium-powder-sds.pdf
    year: 2023
  - title: 'PubChem compound record: Vanadium (CID 23990), GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23990/JSON?heading=GHS+Classification
    year: 2026
  - title: 'NIST Atomic Weights and Isotopic Compositions: vanadium'
    type: database
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=V&all=all&ascii=html
    year: 2026
  - title: Properties of V-4Cr-4Ti (property compilation, courtesy of Mike Billone)
    type: datasheet
    url: https://qedfusion.org/LIB/PROPS/vprop.html
  - title: Reference vanadium alloy V-4Cr-4Ti for fusion application, Smith, Chung, Loomis and Tsai, Argonne National Laboratory
    type: paper
    url: https://digital.library.unt.edu/ark:/67531/metadc667725/m2/1/high_res_d/195723.pdf
    year: 1996
  - title: Hydrogen Permeability of Multiphase V-Ti-Ni Metallic Membranes, Adams and Mickalonis, Savannah River National Laboratory
    type: report
    url: https://sti.srs.gov/fulltext/2005/ms2005619.pdf
    year: 2005
  - title: The role of oxygen uptake and scale formation on the embrittlement of vanadium alloys, Pint and DiStefano, Oxidation of Metals 63, 33-55
    type: paper
    url: https://doi.org/10.1007/s11085-005-1950-7
    year: 2005
gaps:
  - No numeric density, melting point or tensile data for binary V-Nb or V-Ti alloys were found in the sources read. The only V-Nb sources read are a quaternary V-Nb-Ti-Co hydrogen paper (qualitative) and a 1984 Metallurgical Transactions A hydrogen study that was not opened.
  - 'V-Cr-Ti: only V-4Cr-4Ti (and V-5Cr-5Ti heats for the impact row) were read in full. The property compilation gives thermal conductivity, specific heat and expansion for V-5Cr-5Ti only, so those rows were left out.'
  - 'Hydrogen permeation rates from the Savannah River table (Pd 3.3-4.3 x 10-10 and V53-Ti26-Ni21 1.0-3.7 x 10-9 mol H2/(m s)) were not entered: the exponent form and the mol H2/(m s) unit were not checked against the site unit registry. The order-of-magnitude comparison is stated in the story instead.'
  - Irradiated yield strength above 800 MPa at about 390 C was seen only in a search snippet and not in an opened page, so it is not entered.
  - Atomic weights for titanium, chromium and niobium were not checked against NIST. Only vanadium (50.9415) was read, so the recipe gives shares for Cr and Ti.
  - The V-4Cr-4Ti design values (design yield and design ultimate strength), reduction in area and ductile-to-brittle transition temperature use non-canonical snake_case names. Uniform elongation is also snake_case. The canon has no entries for these.
  - 'Composition basis: the Argonne Table 1 heading reads wt.%, but the summary text writes V-4Cr-4Ti without units. The nominal composition is taken from Table 1.'
  - No UNS, ASTM or AMS designation for V-4Cr-4Ti, V-Ti or V-Nb was found in the sources used, so designations are empty.
  - Titanium and niobium production shares were not found (USGS titanium and niobium summaries not opened). Critical-list status for titanium metal and niobium came from the USGS and EU list pages only.
  - Vanadium crustal abundance was not found in the sources used.
  - No space-environment data (outgassing, atomic oxygen, radiation, thermal-vacuum) were found in the sources read.
  - PubChem hazard codes beyond the 'not classified' counts were not in the extract. The SDS covers the powder only; no hazard statement was found for bulk V-4Cr-4Ti.
  - The oxygen embrittlement threshold (0.2 percent oxygen) from a 2022 review was found in a search snippet only, so it is not used.
sources:
  usgs-mcs2026-vanadium:
    title: Mineral Commodity Summaries 2026, Vanadium, February 2026
    id: USGS MCS 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-vanadium.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-crit2025:
    title: About the 2025 List of Critical Minerals (USGS, final list)
    id: Final 2025 List of Critical Minerals
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  ec-crm:
    title: Critical raw materials (European Commission, list under Regulation (EU) 2024/1252)
    id: Regulation (EU) 2024/1252
    url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en
    year: 2024
    kind: web
    license: European Commission web page
  pubchem-vanadium:
    title: 'PubChem compound record: Vanadium (CID 23990), GHS Classification section'
    id: CID 23990; ECHA C and L aggregated notifications
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/23990/JSON?heading=GHS+Classification
    kind: database
    license: PubChem (NCBI), public domain
  nist-vanadium:
    title: 'NIST Atomic Weights and Isotopic Compositions for All Elements: vanadium'
    id: NIST, standard atomic weight of V
    url: https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl?ele=V&all=all&ascii=html
    kind: database
    license: NIST public data
  sds-vanadium-powder:
    title: Safety data sheet, spherical vanadium powder, Stanford Advanced Materials
    id: CAS 7440-62-2; revised 02/02/2023
    url: https://samaterials.com/tds/1697121437-spherical-vanadium-powder-sds.pdf
    kind: datasheet
    license: supplier safety data sheet (cited, not reproduced)
  qedfusion-v4cr4ti:
    title: Properties of V-4Cr-4Ti (property compilation, courtesy of Mike Billone)
    id: Cites ITER Materials Properties Handbook, Davis (1996), and ANL and ORNL reports
    url: https://qedfusion.org/LIB/PROPS/vprop.html
    kind: web
    license: cited, not reproduced
  unt-smith-1996:
    title: Reference vanadium alloy V-4Cr-4Ti for fusion application (Smith, Chung, Loomis and Tsai, Argonne National Laboratory, received 1996)
    id: Argonne National Laboratory, UNT digital library record metadc667725
    url: https://digital.library.unt.edu/ark:/67531/metadc667725/m2/1/high_res_d/195723.pdf
    year: 1996
    kind: paper
    license: US Government report (publicly available)
  srs-vtin:
    title: Hydrogen Permeability of Multiphase V-Ti-Ni Metallic Membranes (Adams and Mickalonis, Savannah River National Laboratory)
    id: SRS report MS2005619
    url: https://sti.srs.gov/fulltext/2005/ms2005619.pdf
    year: 2005
    kind: report
    license: US Government report (publicly available)
  pint-distefano-2005:
    title: The role of oxygen uptake and scale formation on the embrittlement of vanadium alloys (Oxidation of Metals 63, 33-55)
    id: doi:10.1007/s11085-005-1950-7
    url: https://doi.org/10.1007/s11085-005-1950-7
    year: 2005
    kind: paper
    license: publisher page (cited, not reproduced)
  qust-vnbti-co:
    title: Microstructure, hydrogen permeability and ductile-to-brittle transition-hydrogen concentration of (V, Nb)-Ti-Co quaternary alloys (Qingdao University of Science and Technology, author page)
    id: Journal volume 305 (journal not named on the author page)
    url: https://faculty.qust.edu.cn/zhaoping12/en/lwcg/144406/content/310556.htm
    kind: web
    license: author page (cited, not reproduced)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 12
  unreachable: 0
  caveats: 4
  note: 'Values read by an AI assistant on 2026-10-26 from the pages and PDFs named in each entry. Caveats: the V-4Cr-4Ti strength values are from a printed correlation, evaluated at 20 C, not from a test table; no binary V-Nb or V-Ti property data were found; the hydrogen permeation table is not entered; the list statuses come from a summarising fetch of the USGS and EU pages.'
story:
  recipe:
    line: V-4Cr-4Ti is vanadium with about 4 wt.% chromium and 4 wt.% titanium. Argonne's Table 1 gives 4.1Cr-4.3Ti for the 30 kg laboratory heat BL-47, 3.8Cr-3.9Ti for the 500 kg production heat 832665, and 4.9Cr-5.1Ti and 4.6Cr-5.1Ti for two V-5Cr-5Ti heats. Trace impurities in the heats listed were 310 to 440 wppm oxygen and 28 to 220 wppm nitrogen. The Savannah River V-Ti-Ni membrane alloy is 53 wt.% V, 26 wt.% Ti and 21 wt.% Ni, arc melted in argon.
    parts:
      - name: Vanadium
        symbol: V
        share_note: balance of the alloy
        role: The base metal. Argonne cites its inherently low irradiation-induced activity as one reason vanadium-base alloys are candidates for fusion structures.
      - name: Chromium
        symbol: Cr
        share_note: about 4 wt.% nominal (3.8 to 4.9 wt.% in the heats listed in Argonne Table 1)
        role: Alloying addition in the V-Cr-Ti family. Argonne selected V-4Cr-4Ti as the reference composition after screening V-Ti, V-Cr-Ti and V-Ti-Si alloys.
      - name: Titanium
        symbol: Ti
        share_note: about 4 wt.% nominal (3.9 to 5.1 wt.% in the heats listed in Argonne Table 1)
        role: Alloying addition in the V-Cr-Ti family. In the Savannah River membrane alloy (V-Ti-Ni) titanium is a major constituent, at 26 wt.%.
  risk_groups:
    - title: For people
      lead: The powder is a flammable solid in the supplier safety data sheet. Bulk alloy parts have no hazard statement in the sources read.
      level: 1
      verdict: Flammable as powder, no bulk hazard read
      points:
        - label: Vanadium powder
          line: The Stanford Advanced Materials safety data sheet classifies vanadium powder as Flammable solid (H228), with H315, H319 and H335 for skin, eye and respiratory irritation. The signal word is Danger.
        - label: Bulk alloy
          line: No hazard statement was found in the sources read for bulk V-4Cr-4Ti. PubChem records that vanadium does not meet GHS hazard criteria in 95.4 percent of its reports.
        - label: In a fire
          line: The SDS says to use a special powder for metal fires and not water.
    - title: If it fails
      lead: The failure routes are oxygen embrittlement in hot air and hydrogen embrittlement in membranes.
      verdict: Oxygen and hydrogen both embrittle the alloy
      points:
        - label: Hot air
          line: At 500 to 700 C, V-4Cr-4Ti forms a surface oxide. Pint and DiStefano found that the oxide did not prevent embrittlement, and specimens were severely embrittled after a 2000 hr anneal at 700 C.
        - label: Hydrogen
          line: The Qingdao study of V-Nb-Ti-Co alloys says that high hydrogen absorption weakens vanadium-based alloys, and that replacing vanadium with niobium shifted the transition hydrogen concentration about 0.36 H/M.
  why: Vanadium alloys are candidates for fusion-reactor first walls and blankets, where a structural metal must survive high temperatures, neutron damage and contact with lithium. The reference alloy, V-4Cr-4Ti, keeps about 20 percent uniform elongation unirradiated, and still keeps more than 8 percent after irradiation to 28 to 46 dpa at 400 to 600 C. It is also being studied as a hydrogen-permeation membrane. The same vanadium that gives these properties takes up oxygen and hydrogen, so the chemistry must be controlled.
  uses:
    - where: Fusion first wall and blanket
      line: Argonne calls vanadium-base alloys promising for fusion reactor first-wall and blanket structures, citing low activation, good mechanical properties, compatibility with lithium and high thermal conductivity.
    - where: Hydrogen separation membranes
      line: Savannah River measured a V-Ti-Ni membrane with a hydrogen permeation rate an order of magnitude higher than palladium at 22 C, in a laboratory electrochemical test. The alloy is a candidate substitute for costly palladium membranes.
  can_do:
    - label: Strength when unirradiated
      value: 402 MPa yield at 20 C
      benchmark: yield_strength
      line: The printed correlation for V-4Cr-4Ti gives a yield strength of 402 MPa and an ultimate tensile strength of 488 MPa at 20 C (calculated from the published fit).
    - label: Ductility
      value: 20 percent uniform elongation
      line: Argonne reports high ductility, about 20 percent uniform elongation, for the alloys tested from room temperature to 700 C. The reduction in area is greater than 70 percent at 600 C and below.
    - label: Low-temperature toughness
      value: DBTT below -200 C
      benchmark: ductile_brittle_transition_temperature
      line: Charpy tests found the ductile-to-brittle transition temperature below -200 C for the two V-4Cr-4Ti heats and one V-5Cr-5Ti heat.
    - label: Density
      value: 6.05 g/cm3
      benchmark: density
      line: V-4Cr-4Ti has a room-temperature density of 6.05 g/cm3.
  compare: V-4Cr-4Ti has a room-temperature density of 6.05 g/cm3, a melting point of about 1900 C and a Young's modulus of about 125.6 GPa at 20 C. Its unirradiated room-temperature yield strength is about 402 MPa, calculated from the printed correlation rather than read from a test table. The vanadium-based membrane alloy trades structural strength for hydrogen permeability, and its hydrogen absorption is the main weakness.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Melting point
      benchmark: melting_point
    - label: Young's modulus
      benchmark: elastic_modulus
  handling:
    - Keep the powder in a cool, dry place in closed containers, away from oxidizing agents, with adequate ventilation (SDS).
    - Do not use water on a vanadium powder fire; use a special powder for metal fires (SDS).
    - 'Protect hot components from oxygen: the alloy forms a surface oxide at 500 to 700 C that does not stop embrittlement (Pint and DiStefano).'
  good_for:
    - High-temperature structure with low activation for fusion first walls, where Argonne reports good ductility after irradiation (more than 8 percent uniform elongation).
    - 'Hydrogen-permeation membranes as a palladium substitute: the V-Ti-Ni alloy permeated hydrogen about ten times faster than palladium in the SRS test.'
  watch_out:
    - 'Oxygen embrittlement: at 500 to 700 C in air or oxygen, the surface oxide does not prevent embrittlement.'
    - 'Hydrogen embrittlement: high hydrogen absorption weakens vanadium-based membranes.'
    - No tensile data for the binary V-Ti or V-Nb alloys were found, so the quoted strengths apply only to V-4Cr-4Ti.
  verdict: V-4Cr-4Ti is the reference vanadium structural alloy for fusion first walls and blankets, with good ductility and lithium compatibility. Vanadium-based membranes are promising for hydrogen separation, but they embrittle with hydrogen and oxygen, and the sources read give no binary V-Nb or V-Ti property data.