spore: profile
id: kovar
spore_version: 0.2
family: nickel-alloys
name: Kovar
abbreviation: Fe-Ni-Co
role: glass-to-metal sealing alloy
category: metals
type: nickel-superalloys
summary: |
  Kovar is an iron-nickel-cobalt alloy of nominal composition Fe-29Ni-17Co (ASTM F15, UNS K94610, EN 1.3981). Its thermal expansion is close to that of borosilicate glass, so it is used for hermetic glass-to-metal seals in electronic packages and vacuum tubes. The Matthey datasheet gives a mean expansion coefficient of 5.25 ×10⁻⁶/°C from 25 to 450 °C. The alloy has a density of 8.36 g/cm3, a melting point of 1450 °C and a Curie temperature of 435 °C. Annealed strip has a minimum yield strength of 200 MPa.
best_for: 'Hermetic glass-to-metal seals: a mean expansion coefficient of 5.25 ×10⁻⁶/°C from 25 to 450 °C, close to borosilicate glass'
weakest_at: 'Heat conduction and weight: 17.5 W/m °K at 20 °C and a density of 8.36 g/cm3, and a yield strength of only 200 MPa minimum when annealed'
identity:
  formula: 'Fe-29Ni-17Co, nominal: iron balance with 28.0 to 30.0 wt% nickel (nominal 29.00) and 17.0 to 18.0 wt% cobalt (nominal 17.00); maximum Si 0.30, Mn 0.50, C 0.05, P 0.03 and S 0.03 wt% (Matthey composition table; CarTech nominal analysis)'
  source: matthey-kovar
  where: Chemical composition table, rows Fe, Co, Ni (weight %), and the Ni and Co ranges printed in the same table
  designations:
    - system: UNS
      code: K94610
      source: carpenter-kovar
      where: Identification section, UNS Number
    - system: ASTM
      code: F15
      source: matthey-kovar
      where: 'Standards line: meets ASTM F15, DIN 17745, W 1.3981, A 54-301, SEW 38'
    - system: EN
      code: '1.3981'
      source: matthey-kovar
      where: Designation table, EN column
    - system: EN name
      code: FeNi29Co18
      source: matthey-kovar
      where: Designation table, Designation row
    - system: DIN
      code: '17745'
      source: matthey-kovar
      where: 'Standards line: meets the international standards ASTM F15 - DIN 17745'
    - system: AFNOR
      code: A 54-301
      source: matthey-kovar
      where: 'Standards line: meets the international standards ASTM F15 - DIN 17745 - W 1.3981 - A 54-301'
    - system: Trade name
      code: Kovar
      source: carpenter-kovar
      where: Title line and trademark note, CarTech Kovar Alloy
    - system: Trade name
      code: Nilo K
      source: sandia-fenico
      where: Table 1.1.1, Common names and Tradenames, row Fe-29Ni-17Co
    - system: Trade name
      code: Rodar
      source: sandia-fenico
      where: Table 1.1.1, Common names and Tradenames, row Fe-29Ni-17Co
    - system: Trade name
      code: Therlo
      source: sandia-fenico
      where: Table 1.1.1, Common names and Tradenames, row Fe-29Ni-17Co
    - system: Trade name
      code: Lock-Invar
      source: sandia-fenico
      where: Table 1.1.1, Common names and Tradenames, row Fe-29Ni-17Co
tags:
  environments: []
  stresses: []
  applications:
    - electronics-and-chips
properties:
  - benchmark: density
    label: Density, Kovar (Fe-29Ni-17Co)
    value: 8.36
    unit: g/cm3
    scope: material
    conditions:
      grade: Kovar, vacuum melted
      temperature: not stated
      form: rolled products (strip, sheet)
    method: Value printed in a manufacturer datasheet
    status: ground
    note: The Eagle Alloys safety data sheet prints a relative density of about 8.6 g/cc, which is not used here.
    source: matthey-kovar
    where: Physical properties table, row Density (g/cm3), value 8.36
  - benchmark: density
    label: Density, CarTech Kovar (printed in lb/in3)
    value: 0.302
    unit: lb/in3
    scope: material
    conditions:
      grade: CarTech Kovar Alloy
      temperature: not stated
      unit_in_source: 0.3020 lb/in3
    method: Value printed in a manufacturer datasheet, with a specific gravity of 8.36 on the same page
    status: ground
    source: carpenter-kovar
    where: Physical Properties section, rows Specific Gravity (8.36) and Density (0.3020 lb/in³)
  - benchmark: melting_point
    label: Melting point, Kovar
    value: 1450
    unit: °C
    scope: material
    conditions:
      grade: Kovar, vacuum melted
      pressure: not stated
    method: Melting point or melting range printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Physical properties table, row Melting point / Melting range (°C), value 1450
  - benchmark: melting_point
    label: Melting range, CarTech Kovar (printed in °F)
    value: 2640
    unit: °F
    scope: material
    conditions:
      grade: CarTech Kovar Alloy
      unit_in_source: 2640 °F
    method: Melting range printed in a manufacturer datasheet
    status: ground
    source: carpenter-kovar
    where: Physical Properties section, row Melting Range (page 3 of 4)
  - benchmark: curie_temperature
    label: Curie temperature, Kovar
    value: 435
    unit: °C
    scope: material
    conditions:
      grade: Kovar
      unit_in_source: 435 ºC; 815 °F in CarTech datasheet
    method: Value printed in a manufacturer datasheet
    status: ground
    note: Eagle Alloys prints the same Curie point in its physical properties (ESPI prints 435 °C in a search snippet only, not used).
    source: matthey-kovar
    where: Physical properties table, row Curie temperature (°C), value 435
  - benchmark: elastic_modulus
    label: Modulus of elasticity, Kovar
    value: 138
    unit: kN/mm2
    scope: material
    conditions:
      grade: Kovar
      temperature: not stated
      unit_in_source: kN/mm2
    method: Value printed in a manufacturer datasheet
    status: ground
    note: The CarTech datasheet prints 20.0 ×10³ ksi, which is about 138 GPa and agrees.
    source: matthey-kovar
    where: Physical properties table, row Modulus of elasticity (kN/mm2), value 138
  - benchmark: poisson_ratio
    label: Poisson ratio, Kovar
    value: 0.317
    unit: '-'
    scope: material
    conditions:
      grade: Kovar
      temperature: not stated
    method: Value printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Physical properties table, row Poisson ratio, value 0.317
  - benchmark: cte
    label: Coefficient of thermal expansion, annealed, 25 to 100 °C
    value: 5.86
    unit: 10-6/°C
    scope: material
    conditions:
      temperature: 25 to 100 °C
      temper: as annealed
      unit_in_source: 10⁻⁶·/ºC
    method: Mean expansion coefficient printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Physical properties table, row Thermal expansion coefficient as annealed, entry 25 to 100 ºC (5.86)
  - benchmark: cte
    label: Coefficient of thermal expansion, annealed, 25 to 450 °C
    value: 5.25
    unit: 10-6/°C
    scope: material
    conditions:
      temperature: 25 to 450 °C
      temper: as annealed
      unit_in_source: 10⁻⁶·/ºC
    method: Mean expansion coefficient printed in a manufacturer datasheet
    status: ground
    note: Matthey gives the range of close match to borosilicate glass as 80 to 450 °C in its text.
    source: matthey-kovar
    where: Physical properties table, row Thermal expansion coefficient as annealed, entry 25 to 450 ºC (5.25)
  - benchmark: cte
    label: Coefficient of thermal expansion, annealed, 25 to 500 °C
    value: 6.15
    unit: 10-6/°C
    scope: material
    conditions:
      temperature: 25 to 500 °C
      temper: as annealed
      unit_in_source: 10⁻⁶·/ºC
    method: Mean expansion coefficient printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Physical properties table, row Thermal expansion coefficient as annealed, entry 25 to 500 ºC (6.15)
  - benchmark: thermal_conductivity
    label: Thermal conductivity at 20 °C, Kovar
    value: 17.5
    unit: W/m °K
    scope: material
    conditions:
      temperature: 20 °C
      unit_in_source: W/m °K
    method: Value printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Physical properties table, row Thermal conductivity at 20 ºC, value 17.5
  - benchmark: specific_heat
    label: Specific heat at 20 °C, Kovar
    value: 500
    unit: J/(kg. K)
    scope: material
    conditions:
      temperature: 20 °C
      unit_in_source: J/(kg. K)
    method: Value printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Physical properties table, row Specific heat at 20 ºC, value 500
  - benchmark: electrical_resistivity
    label: Electrical resistivity at 20 °C, Kovar
    value: 49
    unit: μΩcm
    scope: material
    conditions:
      temperature: 20 °C
      unit_in_source: μΩcm
    method: Value printed in a manufacturer datasheet
    status: ground
    note: CarTech prints 294 ohm-cir-mil/ft at 70 °F for the same grade, which agrees with the Matthey value and is not repeated.
    source: matthey-kovar
    where: Physical properties table, row Electrical resistivity at 20 ºC, value 49 (μΩcm)
  - benchmark: yield_strength
    label: Yield strength Rp0.2, annealed strip, minimum
    value: 200
    bound: lower
    unit: N/mm2
    scope: material
    conditions:
      temper: annealed
      measure: Rp0.2
      product_form: strip
      unit_in_source: N/mm2
    method: Minimum value printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Mechanical properties of strips table, row annealed, column Rp0.2 (N/mm2), 200 min.
  - benchmark: ultimate_tensile_strength
    label: Tensile strength Rm, annealed strip
    value: 450
    value_high: 585
    bound: range
    unit: N/mm2
    scope: material
    conditions:
      temper: annealed
      product_form: strip
      unit_in_source: N/mm2
    method: Range printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Mechanical properties of strips table, row annealed, column Rm (N/mm2), 450 - 585
  - benchmark: elongation
    label: Elongation A50mm, annealed strip, minimum
    value: 25
    bound: lower
    unit: '%'
    scope: material
    conditions:
      temper: annealed
      gauge_length: 50 mm
      product_form: strip
    method: Minimum value printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Mechanical properties of strips table, row annealed, column A50mm (%), 25 min
  - benchmark: hardness
    label: Hardness HV, annealed strip
    value: 110
    value_high: 170
    bound: range
    unit: HV
    scope: material
    conditions:
      temper: annealed
      product_form: strip
      unit_in_source: HV
    method: Range printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Mechanical properties of strips table, row annealed, column Hardness (HV), 110 - 170
  - benchmark: yield_strength
    label: Yield strength Rp0.2, half-hard strip, minimum
    value: 400
    bound: lower
    unit: N/mm2
    scope: material
    conditions:
      temper: 1/2 hard
      measure: Rp0.2
      product_form: strip
      unit_in_source: N/mm2
    method: Minimum value printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Mechanical properties of strips table, row 1/2 hard, column Rp0.2 (N/mm2), 400 min.
  - benchmark: ultimate_tensile_strength
    label: Tensile strength Rm, half-hard strip
    value: 600
    value_high: 800
    bound: range
    unit: N/mm2
    scope: material
    conditions:
      temper: 1/2 hard
      product_form: strip
      unit_in_source: N/mm2
    method: Range printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Mechanical properties of strips table, row 1/2 hard, column Rm (N/mm2), 600 - 800
  - benchmark: yield_strength
    label: Yield strength Rp0.2, hard strip, minimum
    value: 750
    bound: lower
    unit: N/mm2
    scope: material
    conditions:
      temper: hard
      measure: Rp0.2
      product_form: strip
      unit_in_source: N/mm2
    method: Minimum value printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Mechanical properties of strips table, row hard, column Rp0.2 (N/mm2), 750 min.
  - benchmark: ultimate_tensile_strength
    label: Tensile strength Rm, hard strip, minimum
    value: 830
    bound: lower
    unit: N/mm2
    scope: material
    conditions:
      temper: hard
      product_form: strip
      unit_in_source: N/mm2
    method: Minimum value printed in a manufacturer datasheet
    status: ground
    source: matthey-kovar
    where: Mechanical properties of strips table, row hard, column Rm (N/mm2), 830 min.
corrosion:
  - environment: Humid air (CarTech comparative scale)
    headline: Kovar has moderate humidity resistance on the manufacturer's four-level comparative scale.
    effect: CarTech rates the alloy Moderate for humidity and says the four-level scale is for comparison only. The datasheet adds that temperature, concentration, pH, crevices, surface finish and contact with dissimilar metals all change corrosion resistance, and that corrosion testing is recommended. No corrosion rate is printed.
    rating: moderate
    conditions:
      basis: manufacturer comparative rating; no exposure time or test method printed
    source: carpenter-kovar
    where: Corrosion Resistance section, row Humidity (page 1 of 4)
  - environment: Air at 650 to 700 °C (oxide deliberately grown for glass sealing)
    headline: A thin, tightly adhering dark grey to slight brown oxide is the preferred surface for sealing to hard glass.
    effect: CarTech says the best oxide film is thin and tightly adhering and is formed by heating parts to 650 to 700 °C in ordinary air until a dark grey to slight brown oxide forms. Matthey warns that annealing above 900 °C, or long annealing, causes grain growth. The oxide is intended, so the rating reflects only the process step.
    rating: moderate
    conditions:
      temperature: 650 to 700 °C
      atmosphere: ordinary ambient air
      basis: manufacturer sealing practice; no oxide thickness or rate printed
    source: carpenter-kovar
    where: Preparation for Sealing section, oxide film paragraph (page 1 of 4); grain growth from Matthey heat treatment item 1
  - environment: Hydrogen gas (internal and external, 69 MPa, 430 K)
    headline: Annealed Fe-29Ni-17Co shows no significant hydrogen embrittlement in the published tests.
    effect: Sandia reports that internal hydrogen from thermal precharging (69 MPa at 430 K for 6500 h) left the annealed alloy's reduction of area and notched tensile behaviour essentially unchanged. The notched impact energy was 14.1 J after precharging against 14.3 J unexposed. Sandia notes that very little published data exist and that no fatigue, fracture toughness or weld data in hydrogen were found.
    rating: low
    conditions:
      material: annealed Fe-29Ni-17Co
      pressure: 69 MPa
      temperature: 430 K
      time: 6500 h precharge
      basis: one literature report cited by Sandia
    source: sandia-fenico
    where: Section 3.1.1 smooth and 3.1.2 notched tensile properties; Section 3.5 impact
risks:
  hazards:
    - text: 'Eagle Alloys safety data sheet (revised November 2017): the solid alloy is not classified as hazardous under 29 CFR 1910.1200, and the sheet lists no GHS label elements. Grinding, melting or welding can give dust or fumes, and inhaling the fumes may cause metal fume fever.'
      ghs: []
      source: eagle-sds
      where: Section 2 Hazards identification, GHS Classification and Other Hazard Information
    - text: Nickel is listed by NTP as reasonably anticipated to be a human carcinogen and by IARC as group 2B, although the sheet says metallic nickel is less likely to be carcinogenic than nickel compounds. Nickel can cause an allergic skin reaction. Cobalt is listed by IARC as group 2B and NTP does not list it as carcinogenic. Chronic inhalation of cobalt dust or fume affects the respiratory system.
      ghs: []
      source: eagle-sds
      where: Section 11 Toxicological information, Nickel and Cobalt paragraphs, and Carcinogenicity list
  failure_risks:
    - mode: Grain growth from hot or long annealing
      trigger: Annealing above 900 °C, or prolonged annealing time
      consequence: Matthey says high temperatures and long annealing should be avoided because of grain growth. The datasheet prints no property change for this.
      severity: moderate
      source: matthey-kovar
      where: Heat treatment, item 1
    - mode: Cracked or separated solder joints to copper conductors
      trigger: Thermal expansion differences, rapid vacuum reduction, vibration and high temperature acting on Kovar ribbon leads on printed wiring boards
      consequence: NASA reports that cracked solder or solder separation from copper pads gave electrical discontinuities in earlier systems, and it studied parallel gap welding of gold-plated Kovar ribbon as a stronger joint. The note gives weld quality criteria but no failure rate.
      severity: moderate
      source: nasa-tn-d6236
      where: Section 1 Introduction, paragraph on varying environmental conditions
  side_effects: []
  handling:
    - text: Dust and fume from grinding, melting or welding should be controlled. The Eagle sheet asks for ventilation, local exhaust where possible, respiratory protection when dust or fume is present, and avoidance of breathing dust.
      source: eagle-sds
      where: Section 7 Handling and storage and Section 8 Exposure controls
    - text: 'Exposure limits printed in the Eagle sheet: nickel OSHA PEL 1 mg/m3 and ACGIH TLV 1.5 mg/m3; cobalt OSHA 0.1 mg/m3 and ACGIH 0.02 mg/m3.'
      source: eagle-sds
      where: Section 8 Exposure controls, Exposure Limits table
    - text: Small chips, fine turnings and dust from processing may be ignitable, and a fire gives metal oxide fumes. Keep them away from ignition sources.
      source: eagle-sds
      where: Section 5 Firefighting measures
    - text: Matthey gives a typical anneal of 850 °C for 30 minutes in a protective atmosphere such as wet or dry hydrogen, dissociated ammonia or a similar neutral atmosphere, and warns against temperatures above 900 °C for long times.
      source: matthey-kovar
      where: Heat treatment, items 1 and 2
    - text: CarTech says degassed and fabricated parts should be annealed in wet hydrogen between 838 and 1099 °C (1540 to 2010 °F), with the time falling from about two hours at the lowest temperature to 20 minutes at the highest.
      source: carpenter-kovar
      where: Preparation for Sealing section, heating paragraph (page 1 of 4)
  mitigations: []
uses:
  - application: electronics-and-chips
    device: Hermetic packages for transistors, optoelectronic parts, hybrid circuits, and electron tubes
    example: Matthey lists hybrid circuit casings, transistor and optoelectronic component cases and bases, and tubes for power, microwave and X-ray electronics. CarTech lists power tubes, microwave tubes, transistors, diodes, and the flat-pack and dual-in-line IC packages, all with hermetic glass seals.
    source: matthey-kovar
    where: Typical uses paragraph; CarTech Applications paragraph (carpenter-kovar)
  - application: electronics-and-chips
    device: Kovar ribbon leads on flat-pack electronic packages in aerospace electronics
    example: NASA Marshall Space Flight Center technical note D-6236 (1971) investigated parallel gap welding of gold-plated Kovar ribbon from flat-pack packages to copper printed wiring boards, for aerospace electronics fabrication. The note names no specific spacecraft, rocket or satellite.
    source: nasa-tn-d6236
    where: Summary, and Section 1 Introduction (flat-pack electronic packages and aerospace electronics)
  - application: electronics-and-chips
    device: Glass-to-metal seals for conductors entering glass envelopes
    example: Wikipedia says Kovar is used for glass-to-metal seals in scientific apparatus, and for conductors entering glass envelopes in vacuum tubes, X-ray and microwave tubes, and some lightbulbs.
    source: wikipedia-kovar
    where: Uses paragraph of the Kovar article (history and composition only; no numbers taken from it)
supply:
  - subject: Nickel (mine production, 2025 estimated)
    producers:
      - country: Indonesia
        share_percent: 66.7
        year: 2025
      - country: Philippines
        share_percent: 6.9
        year: 2025
      - country: Russia
        share_percent: 5.1
        year: 2025
      - country: Canada
        share_percent: 3.6
        year: 2025
      - country: New Caledonia
        share_percent: 3.6
        year: 2025
    recycling: 'USGS: nickel recovered from scrap accounted for about 60 % of apparent US consumption in 2025, and most secondary nickel is stainless-steel scrap.'
    substitutes: []
    abundance: 'USGS: world nickel reserves are more than 140,000,000 t, and identified world resources are more than 350 million t.'
    source: usgs-nickel
    where: World Mine Production and Reserves table, 2025e world total 3,900,000 t; producer shares calculated by Space Mushroom from the country values (Indonesia 2,600,000; Philippines 270,000; Russia 200,000; Canada 140,000; New Caledonia 140,000); Recycling paragraph; Reserves and World Resources paragraphs
  - subject: Cobalt (mine production, 2025)
    producers:
      - country: Congo (Kinshasa)
        share_percent: 73
        year: 2025
      - country: Indonesia
        share_percent: 14
        year: 2025
    recycling: 'USGS: cobalt content of purchased scrap was 25 % of estimated US cobalt consumption in 2025. About 51 % of US cobalt consumed in 2025 went to superalloys, mainly for aircraft gas turbine engines.'
    substitutes: []
    abundance: 'USGS: world cobalt reserves are about 12,000,000 t.'
    source: usgs-cobalt
    where: Events, Trends, and Issues paragraph (Congo 73 %, Indonesia 14 % of world total); Recycling paragraph; Domestic Production and Use paragraph; World Mine Production and Reserves table (world reserves 12,000,000 t)
documents:
  - title: Lamineries Matthey KOVAR datasheet (FeNi29Co18, EN 1.3981, UNS K94610), 2025
    type: datasheet
    url: https://www.matthey.ch/fileadmin/user_upload/downloads/fichetechnique/EN/Kovar_v25E.pdf
    year: 2025
  - title: CarTech Kovar Alloy datasheet (UNS K94610), CRS Holdings, edition 10/01/1990, copyright 2020
    type: datasheet
    url: https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/Kovar.pdf
    year: 2020
  - title: 'Sandia National Laboratories, Technical Reference on Hydrogen Compatibility of Materials: Sealing Alloys Fe-Ni-Co (code 2401)'
    type: report
    url: https://www.sandia.gov/app/uploads/sites/158/2021/12/2401TechRef_FeNiCo_kovar.pdf
    year: 2005
  - title: Eagle Alloys Kovar safety data sheet (revised November 2017)
    type: sds
    url: https://www.eaglealloys.com/wp-content/uploads/2020/10/Kovar-Safety-Data-Sheet.pdf
    year: 2017
  - title: 'USGS Mineral Commodity Summaries 2026: Nickel'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nickel.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Cobalt'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-cobalt.pdf
    year: 2026
  - title: 'NASA Technical Note D-6236: Parallel Gap Welding Kovar Ribbons to Copper Conductor Printed Wiring Boards (Marshall Space Flight Center), 1971'
    type: report
    url: https://ntrs.nasa.gov/api/citations/19710009262/downloads/19710009262.pdf
    year: 1971
  - title: 'Wikipedia: Kovar'
    type: database
    url: https://en.wikipedia.org/wiki/Kovar
gaps:
  - No spacecraft, satellite or rocket structure use was found in a fetched source. The only space link is NASA TN D-6236 (1971, Marshall), which covers Kovar ribbon leads for aerospace electronics and names no vehicle. Vendor pages that claim satellite and deep-space use were seen in search results only and are not used.
  - 'No AISI designation: Matthey prints a dash in its AISI column and no fetched source gives one.'
  - UNS K94630 and ASTM F-1466 appear in the same Sandia table row as Fe-29Ni-17Co, but K94630 is a separate grade code (Therlo) and is left out.
  - SEW 38 (listed by Matthey) is not a system in the designation list, so it is left out.
  - 'The CarTech typical mechanical properties table (annealed strip: yield 345 MPa, tensile 517 MPa, elongation 30 % in 2 in, Rockwell B 68) is an image in the PDF. It does not extract as text, so verify-values could not confirm it and these values are left out.'
  - Oxidation kinetics (activation energies for air oxidation, and the Kim et al. humidified-atmosphere work) appear only in search summaries. The source pages could not be fetched in this run, so no oxidation numbers are recorded.
  - No salt-spray or aqueous corrosion rate was read. A Japanese patent claim that plain Kovar has no corrosion resistance was seen only as a search summary and is not used.
  - EU CLP hazard codes for Kovar (H317, H351, H372, from an Ametek sheet) were seen only in search results and the sheet did not open, so no GHS codes are recorded. The US sheet says the alloy is not classified.
  - No critical-minerals list status was read for nickel or cobalt in the fetched USGS summaries. No substitute for Kovar was found in the USGS text.
  - Curie temperature, poisson ratio and hardness use benchmark names that may not be in the canonical list; check against spores/property-canon.yaml.
  - Atomic weights for iron, nickel and cobalt were not read from a fetched page in this run, so the recipe gives composition shares only.
sources:
  matthey-kovar:
    title: KOVAR datasheet, Lamineries Matthey (branch of Notz Metall AG), FeNi29Co18
    id: EN 1.3981, UNS K94610, LMSA F260; ASTM F15, DIN 17745, A 54-301
    url: https://www.matthey.ch/fileadmin/user_upload/downloads/fichetechnique/EN/Kovar_v25E.pdf
    year: 2025
    kind: datasheet
    license: Manufacturer datasheet, informative only (cited, not reproduced)
  carpenter-kovar:
    title: CarTech Kovar Alloy datasheet, Carpenter Technology (CRS Holdings), edition 10/01/1990, copyright 2020
    id: UNS K94610; ASTM F-15
    url: https://www.carpentertechnology.com/hubfs/7407324/Material%20Saftey%20Data%20Sheets/Kovar.pdf
    year: 2020
    kind: datasheet
    license: Manufacturer datasheet, typical values only (cited, not reproduced)
  sandia-fenico:
    title: 'Technical Reference on Hydrogen Compatibility of Materials: Specialty Steels, Sealing Alloys Fe-Ni-Co (code 2401), Sandia National Laboratories'
    id: Table 1.1.1 nominal composition and designations; Section 3 hydrogen tests
    url: https://www.sandia.gov/app/uploads/sites/158/2021/12/2401TechRef_FeNiCo_kovar.pdf
    year: 2005
    kind: report
    license: Public technical reference (cited, not reproduced)
  eagle-sds:
    title: Kovar Safety Data Sheet, Eagle Alloys Corporation (revised November 2017)
    url: https://www.eaglealloys.com/wp-content/uploads/2020/10/Kovar-Safety-Data-Sheet.pdf
    year: 2017
    kind: datasheet
    license: Supplier safety data sheet (cited, not reproduced)
  usgs-nickel:
    title: 'Mineral Commodity Summaries 2026: Nickel, U.S. Geological Survey'
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-nickel.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-cobalt:
    title: 'Mineral Commodity Summaries 2026: Cobalt, U.S. Geological Survey'
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-cobalt.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  nasa-tn-d6236:
    title: 'NASA Technical Note D-6236: Parallel Gap Welding Kovar Ribbons to Copper Conductor Printed Wiring Boards, G. E. McDaniel, George C. Marshall Space Flight Center'
    id: NTRS 19710009262
    url: https://ntrs.nasa.gov/api/citations/19710009262/downloads/19710009262.pdf
    year: 1971
    kind: report
    license: public domain (NASA)
  wikipedia-kovar:
    title: Kovar, Wikipedia
    url: https://en.wikipedia.org/wiki/Kovar
    kind: web
    license: CC BY-SA 4.0 (cited, not reproduced)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 21
  unreachable: 0
  caveats: 4
  note: 'Values were read by an AI assistant on 2026-10-26 from the datasheets, SDS, USGS summaries and NASA note named in each entry. The CarTech typical strength values sit in an image table that does not extract as text, so they are left out. Wikipedia is used for uses and history only. The nickel producer shares are calculated from the USGS world total. Caveats: the strength values come from manufacturer typical or minimum data for one strip product, the Carpenter values are typical, the cobalt and nickel supply figures are 2025 estimates, and the aerospace use rests on a 1971 NASA electronics note.'
story:
  risk_groups:
    - title: For people
      level: 1
      verdict: Not classified as hazardous by the supplier sheet
      lead: The solid alloy is not classified under US hazard rules, but its nickel and cobalt content gives carcinogenicity and sensitisation concerns when it is ground, melted or welded.
      points:
        - label: The solid alloy
          line: The Eagle Alloys sheet says the solid form is not classified as hazardous and presents few health hazards under normal handling.
        - label: Dust and fume
          line: Grinding, melting or welding can give dust or metal fume, which can cause metal fume fever. Both nickel and cobalt are listed by IARC as group 2B.
    - title: If it fails
      lead: These are failure routes found in the sources. None is a measured field failure rate.
      points:
        - label: Over-annealing
          line: Annealing above 900 °C, or for a long time, causes grain growth, according to Matthey.
        - label: Solder joints
          line: NASA's 1971 note found that cracked or separated solder to copper pads caused electrical discontinuities, and it tested gold-plated Kovar ribbon welds as a stronger joint.
        - label: Hydrogen
          line: Sandia found no significant hydrogen effect on annealed Fe-29Ni-17Co in its tests, which were limited to one literature report.
    - title: Handling and storage
      points:
        - label: Anneal in a protective atmosphere
          line: Matthey gives a typical anneal of 850 °C for 30 minutes in wet or dry hydrogen, dissociated ammonia or another neutral atmosphere. CarTech asks for a wet hydrogen anneal between 838 and 1099 °C to avoid surface carbon pickup.
        - label: Keep dust under control
          line: The Eagle sheet asks for ventilation and respiratory protection when dust or fume is present.
  why: Kovar is an iron-nickel-cobalt alloy, nominally Fe-29Ni-17Co, made to match the thermal expansion of borosilicate glass. Matthey gives a mean expansion coefficient of 5.25 ×10⁻⁶/°C from 25 to 450 °C, and says the match holds from 80 to 450 °C. Glass seals depend on that match, because a metal that expands much more than the glass cracks the seal when the part cools. The alloy is therefore sealed into borosilicate glass in electronic packages and electron tubes. Its density is 8.36 g/cm3 and its melting point is 1450 °C.
  uses:
    - where: Electronic packages
      line: Matthey lists hybrid circuit casings, transistor and optoelectronic cases and bases, and tubes for power, microwave and X-ray electronics. CarTech adds flat-pack and dual-in-line integrated circuit packages.
    - where: Aerospace electronics
      line: A NASA Marshall technical note from 1971 studied welding Kovar ribbon leads from flat-pack packages to copper boards for aerospace electronics fabrication. The note names no particular spacecraft, rocket or satellite.
    - where: Glass-to-metal seals
      line: Wikipedia says the alloy seals conductors into glass envelopes in vacuum tubes, X-ray and microwave tubes, some lightbulbs and scientific apparatus.
  can_do:
    - label: Seal to glass
      value: 5.25 ×10⁻⁶/°C
      benchmark: cte
      line: The mean expansion coefficient from 25 to 450 °C is 5.25 ×10⁻⁶/°C, close to borosilicate glass, so the joint holds when the part cools.
    - label: Density
      value: 8.36 g/cm3
      benchmark: density
      line: Density is 8.36 g/cm3 in the Matthey datasheet, and CarTech prints a specific gravity of 8.36 and 0.3020 lb/in3.
    - label: Melting
      value: 1450 °C
      benchmark: melting_point
      line: Matthey gives a melting point or range of 1450 °C, and CarTech prints a melting range of 2640 °F.
    - label: Heat conduction
      value: 17.5 W/m °K
      benchmark: thermal_conductivity
      line: Thermal conductivity at 20 °C is 17.5 W/m °K, and electrical resistivity is 49 μΩcm at 20 °C.
    - label: Strength when annealed
      value: 200 MPa minimum yield
      benchmark: yield_strength
      line: Annealed strip has a minimum Rp0.2 of 200 N/mm2 and a tensile strength of 450 to 585 N/mm2 (Matthey).
  compare: Matthey says the expansion of Kovar is similar to borosilicate glass and to alumina ceramics over 80 to 450 °C. Sandia lists Fe-29Ni-17Co for borosilicate glass and Fe-27Ni-25Co, a different grade, for alumina, so match the grade to the seal material. The rows below are read as properties of this one alloy and are not ranked against other materials.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Thermal expansion 25 to 450 °C
      benchmark: cte
    - label: Thermal conductivity at 20 °C
      benchmark: thermal_conductivity
  handling:
    - Specify the temper, because yield strength rises from 200 MPa annealed to 750 MPa minimum in the hard temper.
    - Anneal in hydrogen or another protective atmosphere, and do not hold above 900 °C for long, to avoid grain growth.
    - Control dust and fume from grinding, melting and welding, since nickel and cobalt are both classed by IARC as group 2B.
  good_for:
    - 'Hermetic glass seals: a mean expansion coefficient of 5.25 ×10⁻⁶/°C from 25 to 450 °C.'
    - Electronic packages and electron tubes with glass-sealed leads.
    - No hydrogen embrittlement found in annealed Fe-29Ni-17Co in the published tests.
  watch_out:
    - Heat conduction is low at 17.5 W/m °K, and density is 8.36 g/cm3.
    - Annealed yield strength is only 200 MPa minimum (Matthey).
    - Nickel and cobalt are IARC group 2B, and the alloy gives dust and fume when worked hot.
    - No aqueous corrosion data, satellite flight data or salt-spray rate was found for this profile.
  verdict: 'Kovar is the standard iron-nickel-cobalt glass-sealing alloy: its expansion of 5.25 ×10⁻⁶/°C from 25 to 450 °C matches borosilicate glass, so it is used in hermetic electronic packages and electron tubes. It is dense, has low heat conduction, and is soft when annealed. The space use found is a 1971 NASA electronics note, not a flight record.'
  recipe:
    line: Kovar is a single-phase austenitic iron-nickel-cobalt alloy, vacuum melted, of nominal composition Fe-29Ni-17Co (Matthey; CarTech; Sandia). Matthey gives the composition limits in weight per cent. Its silicon, manganese, carbon, phosphorus and sulphur limits are 0.30, 0.50, 0.05, 0.03 and 0.03 wt% maximum. Annealing is typically 850 °C for 30 minutes in a protective atmosphere.
    parts:
      - name: Iron
        symbol: Fe
        share_note: balance (CarTech and Matthey composition tables)
        role: The matrix. Sandia states that the alloy is single-phase austenite with relatively low strength (below 700 MPa).
      - name: Nickel
        symbol: Ni
        share_percent: 28
        share_high: 30
        share_note: wt%, nominal 29.00 (CarTech)
        role: Sets the expansion and makes the alloy match borosilicate glass. Glass-sealing performance depends on this composition.
      - name: Cobalt
        symbol: Co
        share_percent: 17
        share_high: 18
        share_note: wt%, nominal 17.00 (CarTech)
        role: Works with nickel to set the low expansion over the glass sealing range from 80 to 450 °C.