Gamma titanium aluminide (TiAl), Ti-48Al-2Cr-2Nb turbine-blade alloy TiAl

spore: profile
id: titanium-aluminide
spore_version: 0.2
family: titanium-alloys
name: Gamma titanium aluminide (TiAl), Ti-48Al-2Cr-2Nb turbine-blade alloy
abbreviation: TiAl
role: high-temperature structural intermetallic
category: metals
type: titanium
summary: |
  Gamma titanium aluminide (gamma TiAl) is an intermetallic compound of titanium and about 48 at. % aluminium, usually with small chromium and niobium additions. It is not a conventional titanium alloy. NASA gives its density as 3.8 g/cm3 for the gamma family. Cast to size, the Ti-48Al-2Cr-2Nb alloy has a room-temperature 0.2 % offset yield strength of 326 MPa, a tensile strength of 422 MPa and only 1.70 % elongation. GE manufactured and engine-tested low-pressure turbine blades from this alloy in 1993, and uses TiAl low-pressure turbine blades in its GEnx and LEAP engines. Low room-temperature ductility is the main limit.
best_for: Light rotating parts that run hot, such as low-pressure turbine blades in GE engines, where a density near 3.8 g/cm3 and a stiffness of 168 GPa matter more than ductility
weakest_at: Room-temperature ductility, since cast Ti-48-2-2 elongates only 1.70 % at 23 degC and impact can crack thin sections
identity:
  formula: 'Ti-48Al-2Cr-2Nb (at. %): gamma TiAl with 2 at. % Cr and 2 at. % Nb. The alpha-2 class is Ti3Al'
  cas: ''
  structure_note: Alpha-2 Ti3Al has an ordered hexagonal D019 crystal structure (Wikipedia, Alpha 2-Ti3Al section)
  source: nasa-2004
  where: 'Introduction and Materials sections: Ti-48Al-2Cr-2Nb (at.%) is the GEAE low-pressure turbine blade alloy'
tags:
  environments: []
  stresses: []
  applications:
    - propulsion-and-tanks
    - structures
composition:
  basis: atomic percent (at. %)
  source: nasa-2004
  where: Introduction (Ti-48Al-2Cr-2Nb (at.%)); Materials, chemistry paragraph
  nominal: 'Ti-48Al-2Cr-2Nb: 48 at. % Al, 2 at. % Cr, 2 at. % Nb, balance titanium'
  measured_al: 47.5 at. % Al by x-ray fluorescence in the cast-to-size Ti-48-2-2 samples
  note: NASA also tested Ti-47-2-2 (47.1 at. % Al) and a 46.5 at. % Al slab
properties:
  - benchmark: density
    label: Density, gamma TiAl family
    value: 3.8
    unit: g/cm3
    scope: material
    conditions:
      basis: gamma TiAl alloy family, as printed in the report introduction (not one composition)
    method: Value printed in the introduction of NASA TM 2004-212303
    status: ground
    source: nasa-2004
    where: Introduction, first paragraphs (the sentence giving low density (3.8 g/cm3))
  - benchmark: density
    label: Density, gamma class
    value: 4.04
    unit: g/cm3
    scope: material
    conditions:
      basis: gamma class (gamma plus alpha-2 two-phase alloys) column of Table I
    method: Value printed in a comparison table of titanium aluminides, titanium alloys and superalloys (GE Aircraft Engines, 1992)
    status: ground
    source: gaa-1992
    where: Table I, Density g/cm3 row, Gamma column
  - benchmark: density
    label: Density, alpha-2 class (Ti3Al based)
    value: 4.84
    unit: g/cm3
    scope: material
    conditions:
      basis: alpha-2 class (alpha-2 plus beta alloys) column of Table I
    method: Value printed in a comparison table of titanium aluminides, titanium alloys and superalloys (GE Aircraft Engines, 1992)
    status: ground
    source: gaa-1992
    where: Table I, Density g/cm3 row, Alpha-2 column
  - benchmark: density
    label: Density, titanium alloy class (for comparison, not TiAl)
    value: 4.54
    unit: g/cm3
    scope: material
    conditions:
      basis: Ti alloys column of Table I, class average for comparison
    method: Value printed in a comparison table (GE Aircraft Engines, 1992)
    status: ground
    source: gaa-1992
    where: Table I, Density g/cm3 row, Ti Alloys column
  - benchmark: density
    label: Density, superalloy class (for comparison)
    value: 8.3
    unit: g/cm3
    scope: material
    conditions:
      basis: Superalloys column of Table I, class average for comparison
    method: Value printed in a comparison table (GE Aircraft Engines, 1992)
    status: ground
    source: gaa-1992
    where: Table I, Density g/cm3 row, Superalloys column
  - benchmark: elastic_modulus
    label: Elastic modulus, cast-to-size Ti-48-2-2, 23 degC
    value: 168
    unit: GPa
    scope: material
    conditions:
      alloy: Ti-48Al-2Cr-2Nb cast to size
      temperature: 23 degC
      test: tabulated average; method not printed in the table
    method: Average elastic modulus printed in the tensile property table of NASA TM 2004-212303
    status: ground
    source: nasa-2004
    where: Table VII, Average tensile properties for gamma TiAl alloys, Cast-to-size Ti-48-2-2 row, 23 degC, Elastic modulus column
  - benchmark: elastic_modulus
    label: Elastic modulus, cast-to-size Ti-48-2-2, 650 degC
    value: 141
    unit: GPa
    scope: material
    conditions:
      alloy: Ti-48Al-2Cr-2Nb cast to size
      temperature: 650 degC
      test: tabulated average; method not printed in the table
    method: Average elastic modulus printed in the tensile property table of NASA TM 2004-212303
    status: ground
    source: nasa-2004
    where: Table VII, Cast-to-size Ti-48-2-2 row, 650 degC, Elastic modulus column
  - benchmark: elastic_modulus
    label: Stiffness, gamma class
    value: 176
    unit: GPa
    scope: material
    conditions:
      basis: gamma class (gamma plus alpha-2 two-phase alloys), class value from Table I
    method: Value printed in a comparison table (GE Aircraft Engines, 1992)
    status: ground
    source: gaa-1992
    where: Table I, Stiffness GPa row, Gamma column
  - benchmark: elastic_modulus
    label: Stiffness, alpha-2 class (Ti3Al based)
    value: 145
    unit: GPa
    scope: material
    conditions:
      basis: alpha-2 class (alpha-2 plus beta alloys), class value from Table I
    method: Value printed in a comparison table (GE Aircraft Engines, 1992)
    status: ground
    source: gaa-1992
    where: Table I, Stiffness GPa row, Alpha-2 column
  - benchmark: elastic_modulus
    label: Stiffness, titanium alloy class (for comparison)
    value: 110
    unit: GPa
    scope: material
    conditions:
      basis: Ti alloys column of Table I, class value for comparison
    method: Value printed in a comparison table (GE Aircraft Engines, 1992)
    status: ground
    source: gaa-1992
    where: Table I, Stiffness GPa row, Ti Alloys column
  - benchmark: elastic_modulus
    label: Stiffness, superalloy class (for comparison)
    value: 207
    unit: GPa
    scope: material
    conditions:
      basis: Superalloys column of Table I, class value for comparison
    method: Value printed in a comparison table (GE Aircraft Engines, 1992)
    status: ground
    source: gaa-1992
    where: Table I, Stiffness GPa row, Superalloys column
  - benchmark: yield_strength
    label: 0.2 % yield strength, cast-to-size Ti-48-2-2, 23 degC
    value: 326
    unit: MPa
    scope: material
    conditions:
      alloy: Ti-48Al-2Cr-2Nb cast to size
      temperature: 23 degC
      offset: 0.2 %
    method: Average printed in the tensile property table of NASA TM 2004-212303
    status: ground
    source: nasa-2004
    where: Table VII, Cast-to-size Ti-48-2-2 row, 23 degC, Yield strength column
  - benchmark: yield_strength
    label: 0.2 % yield strength, cast-to-size Ti-48-2-2, 650 degC
    value: 284
    unit: MPa
    scope: material
    conditions:
      alloy: Ti-48Al-2Cr-2Nb cast to size
      temperature: 650 degC
      offset: 0.2 %
    method: Average printed in the tensile property table of NASA TM 2004-212303
    status: ground
    source: nasa-2004
    where: Table VII, Cast-to-size Ti-48-2-2 row, 650 degC, Yield strength column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, cast-to-size Ti-48-2-2, 23 degC
    value: 422
    unit: MPa
    scope: material
    conditions:
      alloy: Ti-48Al-2Cr-2Nb cast to size
      temperature: 23 degC
    method: Average printed in the tensile property table of NASA TM 2004-212303
    status: ground
    source: nasa-2004
    where: Table VII, Cast-to-size Ti-48-2-2 row, 23 degC, Tensile strength column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, cast-to-size Ti-48-2-2, 650 degC
    value: 474
    unit: MPa
    scope: material
    conditions:
      alloy: Ti-48Al-2Cr-2Nb cast to size
      temperature: 650 degC
    method: Average printed in the tensile property table of NASA TM 2004-212303
    status: ground
    source: nasa-2004
    where: Table VII, Cast-to-size Ti-48-2-2 row, 650 degC, Tensile strength column
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, GE gamma alloy, room temperature
    value: 620
    unit: MPa
    scope: material
    conditions:
      basis: gamma alloys developed at GE, best typical values in Table II (alloy not named)
      temperature: 23 degC
      elongation: 3 %
    method: Value printed in a table of recent property highlights (GE Aircraft Engines, 1992)
    status: ground
    source: gaa-1992
    where: Table II, Gamma column, first row
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, GE gamma alloy, 760 degC
    value: 550
    unit: MPa
    scope: material
    conditions:
      basis: gamma alloys developed at GE, Table II (alloy not named)
      temperature: 760 degC
    method: Value printed in a table of recent property highlights (GE Aircraft Engines, 1992)
    status: ground
    source: gaa-1992
    where: Table II, Gamma column, second row
  - benchmark: elongation
    label: Elongation, cast-to-size Ti-48-2-2, 23 degC
    value: 1.7
    unit: '%'
    scope: material
    conditions:
      alloy: Ti-48Al-2Cr-2Nb cast to size
      temperature: 23 degC
    method: Average printed in the tensile property table of NASA TM 2004-212303
    status: ground
    source: nasa-2004
    where: Table VII, Cast-to-size Ti-48-2-2 row, 23 degC, Elongation percent column
  - benchmark: elongation
    label: Elongation, cast-to-size Ti-48-2-2, 650 degC
    value: 5.1
    unit: '%'
    scope: material
    conditions:
      alloy: Ti-48Al-2Cr-2Nb cast to size
      temperature: 650 degC
    method: Average printed in the tensile property table of NASA TM 2004-212303
    status: ground
    source: nasa-2004
    where: Table VII, Cast-to-size Ti-48-2-2 row, 650 degC, Elongation percent column
  - benchmark: max_creep_temperature
    label: Maximum temperature for creep, gamma class
    value: 900
    unit: degC
    scope: material
    conditions:
      basis: gamma class column of Table I, class value
    method: Value printed in a comparison table (GE Aircraft Engines, 1992); not a measured creep limit for one alloy
    status: ground
    source: gaa-1992
    where: Table I, Max T - Creep row, Gamma column
  - benchmark: max_oxidation_temperature
    label: Maximum temperature for oxidation, gamma class
    value: 815
    unit: degC
    scope: material
    conditions:
      basis: gamma class column of Table I, class value; test atmosphere not printed
    method: Value printed in a comparison table (GE Aircraft Engines, 1992)
    status: ground
    source: gaa-1992
    where: Table I, Max T - Oxidation row, Gamma column
  - benchmark: max_oxidation_temperature
    label: Maximum temperature for oxidation, alpha-2 class
    value: 705
    unit: degC
    scope: material
    conditions:
      basis: alpha-2 class column of Table I, class value; test atmosphere not printed
    method: Value printed in a comparison table (GE Aircraft Engines, 1992)
    status: ground
    source: gaa-1992
    where: Table I, Max T - Oxidation row, Alpha-2 column
corrosion:
  - environment: Air at high temperature (oxidation)
    headline: Gamma TiAl is tabulated to resist oxidation up to 815 degC; alpha-2 Ti3Al to 705 degC.
    effect: GE's comparison table gives the maximum oxidation temperature as 815 degC for the gamma class and 705 degC for the alpha-2 class. Its text calls gamma alloys excellent in oxidation resistance. The test atmosphere and exposure time are not printed.
    rating: low
    conditions:
      basis: class values from a 1992 review table; no Ti-48Al-2Cr-2Nb test is described
    source: gaa-1992
    where: Table I, Max T - Oxidation row; Table II, Gamma column (Excellent oxidation resistance)
  - environment: Elevated temperature in general (oxidation and corrosion)
    headline: Wikipedia cites oxidation and corrosion resistance at elevated temperatures for TiAl, above about 600 degC.
    effect: The encyclopedia article says the alloys combine excellent mechanical properties with oxidation and corrosion resistance at elevated temperatures, over 600 degC. It is a general statement with no test conditions.
    rating: low
    conditions:
      basis: general statement in an encyclopedia article; no test conditions
    source: wiki-tial
    where: Gamma-TiAl passage in the article
risks:
  hazards:
    - text: PubChem gives titanium (CID 23963) the GHS codes H228 (flammable solid), H250 (catches fire spontaneously if exposed to air) and H251 (self-heating; may catch fire), from ECHA C and L notifications. 606 of 808 company reports say it does not meet GHS hazard criteria.
      ghs:
        - 'H228: Flammable solid'
        - 'H250: Catches fire spontaneously if exposed to air'
        - 'H251: Self-heating; may catch fire'
      source: pubchem-ti
      where: Safety and Hazards, Hazards Identification, GHS Classification (CID 23963)
    - text: PubChem gives aluminum (CID 5359268) the GHS codes H250 (34.2 %), H261 (90.8 %) and H228 (60.6 %) from company reports. H261 means that it releases flammable gas in contact with water.
      ghs:
        - 'H250: Catches fire spontaneously if exposed to air'
        - 'H261: In contact with water releases flammable gas'
        - 'H228: Flammable solid'
      source: pubchem-al
      where: Safety and Hazards, GHS Classification (CID 5359268)
  failure_risks:
    - mode: Low room-temperature ductility
      trigger: Loading at 23 degC, including impact
      consequence: Cast-to-size Ti-48-2-2 elongates 1.70 % at 23 degC. NASA's program was set up because the limited ductility of gamma TiAl raised a concern about impact resistance.
      severity: high
      source: nasa-2004
      where: Introduction (first paragraphs); Table VII, 23 degC row
    - mode: Cracking from impact
      trigger: Impact tests at 260 degC in air under a 70 MPa tensile load, simulating LPT blade operating conditions
      consequence: At higher impact energies, circumferential cracks grew through the thickness. At extreme energies a cone-shaped piece was removed (blowout), most often in the thin specimens.
      severity: high
      source: nasa-2004
      where: Crack Morphology section (cast-to-size Ti-48-2-2)
    - mode: Casting porosity limits fatigue strength
      trigger: High-cycle fatigue of unfretted and fretted specimens
      consequence: The flat part of the stress-life curve is attributed to a high density of casting pores, which also masked the effect of fretting.
      severity: moderate
      source: nasa-2002
      where: Results, stress-life curves of unfretted and fretted specimens
    - mode: Strength and ductility depend on aluminium content
      trigger: Change of Al level from 48 at. % to 47.1 or 46.5 at. %
      consequence: NASA reports that the strength and ductility of Ti-48Al-2Cr-2Nb vary with Al content, and that 47.1 at. % Al gave higher room-temperature yield strength at the same elongation.
      severity: moderate
      source: nasa-2004
      where: Materials, chemistry paragraph
  side_effects: []
  handling:
    - text: 'Shipping of titanium powder: PubChem''s DOT summary gives the shipping name for titanium powder wetted with not less than 25 percent water (a visible excess of water must be present), for mechanically produced particles under 53 microns.'
      source: pubchem-ti
      where: Safety and Hazards, DOT Hazard Classification (CID 23963)
    - text: Test specimens were cast to size and the blades were cast overstock. The sources read give no heat-treatment window for the blade alloy.
      source: nasa-2004
      where: Introduction and Materials sections
  mitigations: []
uses:
  - application: propulsion-and-tanks
    device: Low-pressure turbine blades, GEnx engine
    example: GE uses gamma TiAl for the low-pressure turbine blades on its GEnx engine, which powers the Boeing 787 and 747-8 and entered service in 2011.
    source: wiki-tial
    where: Applications section, GEnx paragraph
  - application: propulsion-and-tanks
    device: Low-pressure turbine blades, LEAP engine (CFM International)
    example: GE Aerospace lists the titanium aluminide low-pressure turbine blades among the LEAP engine's state-of-the-art technologies and materials.
    source: ge-leap-avio
    where: Article A LEAP for Avio Aero, sentence on the LEAP technologies and materials
  - application: propulsion-and-tanks
    device: Engine-tested low-pressure turbine blades, Ti-48Al-2Cr-2Nb (GE, 1993)
    example: GE Aircraft Engines manufactured low-pressure turbine blades from Ti-48Al-2Cr-2Nb and engine tested them in 1993. NASA then funded a team to optimise the design for commercial service.
    source: nasa-2004
    where: Introduction, first paragraph
supply:
  - subject: Titanium sponge (feedstock for the titanium in TiAl)
    producers:
      - country: China
        share_percent: 70.3
        year: 2025
      - country: Japan
        share_percent: 14.3
        year: 2025
      - country: Russia
        share_percent: 6.8
        year: 2025
      - country: Kazakhstan
        share_percent: 4.3
        year: 2025
      - country: Saudi Arabia
        share_percent: 3.2
        year: 2025
    us_position: The US produced no titanium sponge in 2025 and imported an estimated 44,000 t (net import reliance 100 % in 2025e).
    critical_lists:
      - list: USGS 2025 List of Critical Minerals
        listed: true
    recycling: 'USGS: titanium scrap imports were an estimated 32,000 t in 2025.'
    substitutes:
      - 'USGS: titanium competes with aluminum, composites, intermetallics, steel and superalloys in high-strength applications.'
    source: usgs-ti-2026
    where: World Sponge Metal Production table, 2025 column (world total 370,000 t, shares computed); Salient Statistics; Events, Trends, and Issues; Substitutes
  - subject: Aluminum (matrix element, about 48 at. %)
    producers:
      - country: China
        share_percent: 60.8
        year: 2025
      - country: India
        share_percent: 5.7
        year: 2025
      - country: Russia
        share_percent: 5.3
        year: 2025
      - country: Canada
        share_percent: 4.5
        year: 2025
      - country: United Arab Emirates
        share_percent: 3.6
        year: 2025
    us_position: US smelter production was 660 thousand t in 2025e, against 1.31 million tons per year of domestic smelter capacity. Canada supplied 56 % of imports in 2021 to 2024.
    critical_lists:
      - list: USGS 2025 List of Critical Minerals
        listed: true
    recycling: 'USGS: aluminum recovered from purchased scrap in the US was about 3.6 million tons in 2025.'
    source: usgs-al-2026
    where: World Smelter Production and Capacity table, 2025e column (world total 74,000 thousand t, shares computed); Salient Statistics; Import Sources; Recycling
  - subject: Chromium (alloy addition, 2 at. %)
    producers:
      - country: South Africa
        share_percent: 45.1
        year: 2025
      - country: Turkey
        share_percent: 17.6
        year: 2025
      - country: Kazakhstan
        share_percent: 13.7
        year: 2025
      - country: India
        share_percent: 5.9
        year: 2025
    us_position: The US had no mine production. The US consumed an estimated 4 % of world chromite ore in 2025, and South Africa supplied 96 % of chromite ore imports in 2021 to 2024.
    critical_lists:
      - list: USGS 2025 List of Critical Minerals
        listed: true
    source: usgs-cr-2026
    where: World Mine Production and Reserves table, 2025e column (chromium content, world total 51,000 thousand t, shares computed); Domestic Production and Use; Import Sources
  - subject: Niobium (alloy addition, 2 at. %)
    producers:
      - country: Brazil
        share_percent: 93
        year: 2025
      - country: Canada
        share_percent: 5
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals
        listed: true
    source: usgs-nb-2026
    where: Domestic Production and Use text (Brazil about 93 % of global production; Canada 5 %); World Mine Production table, 2025e column (Brazil 104,000 t of 112,000 t world total)
supply_note: Shares are computed by the assistant from the printed tonnage and the printed world total (USGS rounds its world totals), not printed by USGS, except the niobium shares which USGS prints as percentages.
media: []
documents:
  - title: 'NASA/TM-2004-212303: Durability Assessment of Gamma TiAl, Final Report (Draper et al.)'
    type: report
    url: https://ntrs.nasa.gov/api/citations/20040028027/downloads/20040028027.pdf
    year: 2004
  - title: 'NASA/TM-2002-211718: Preliminary Study on Fatigue Strengths of Fretted Ti-48Al-2Cr-2Nb (Miyoshi et al.)'
    type: report
    url: https://ntrs.nasa.gov/api/citations/20020081267/downloads/20020081267.pdf
    year: 2002
  - title: Titanium Aluminides for Aerospace Applications (Chesnutt, Superalloys 1992, pp. 381-389)
    type: paper
    url: https://www.tms.org/Superalloys/10.7449/1992/Superalloys_1992_381_389.pdf
    year: 1992
  - title: 'PubChem: Titanium (CID 23963), GHS classification and DOT summary'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/23963
    year: 2026
  - title: 'PubChem: Aluminum (CID 5359268), GHS classification'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/5359268
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Titanium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-titanium.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Aluminum'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-aluminum.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Chromium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
  - title: 'USGS Mineral Commodity Summaries 2026: Niobium'
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-niobium.pdf
    year: 2026
gaps:
  - Designations (UNS, EN, AMS, ASTM) for gamma TiAl or Ti-48Al-2Cr-2Nb were not printed on any page read in this run, so identity.designations is left out.
  - Density of the Ti-48Al-2Cr-2Nb alloy itself (about 3.9 g/cm3 is often quoted) was not found in a fetched source. The 3.8 and 4.04 g/cm3 values are family and class figures.
  - Young's modulus for the blade alloy comes from one tabulated cast-to-size value (168 GPa) and one class value (176 GPa). No second source checked them.
  - Fatigue, creep and tensile data above 650 degC for the blade alloy were not extracted. The 1992 creep limit is a class value, not a test.
  - The room-temperature ductility range of the gamma class (1 to 3 %) in the 1992 table was not used, because the text layer of that PDF is garbled at that row.
  - The oxidation test atmosphere, exposure time and scale data were not found. The OSTI abstract on Ti-48Al-2Nb-2Cr oxidation could not be reached in this run.
  - 'Hydrogen embrittlement, galling and seawater or chloride behaviour: no fetched source.'
  - 'Space and vacuum data (outgassing, atomic oxygen erosion, thermal cycling in orbit): no source read.'
  - Blade manufacturing route (electron beam melting, casting suppliers) and the RTI supply agreement for LEAP blades appear only in search snippets, so they are not used.
  - The LEAP claim rests on one sentence in a GE Aerospace article. The LEAP blade process is not confirmed.
  - Alpha-2 Ti3Al figures are class averages from the 1992 GE table, not measurements of Ti3Al alone. Wikipedia gives only the D019 crystal structure.
  - Crustal abundance of titanium, aluminum, chromium and niobium was not extracted from a fetched source.
  - The EU critical raw materials list was not read. Only the USGS 2025 list was checked, from its web page.
  - 'Two property names are not in spores/property-canon.yaml and are used as new names: max_creep_temperature and max_oxidation_temperature.'
  - Wikipedia states that some alloys keep oxidation resistance to 1,000 degC, but the page marks that claim as not specific enough to verify, so it is not used.
sources:
  nasa-2004:
    title: 'NASA/TM-2004-212303: Durability Assessment of Gamma TiAl, Final Report'
    id: NASA TM 2004-212303, Draper, Lerch, Pereira, Miyoshi and Arya
    url: https://ntrs.nasa.gov/api/citations/20040028027/downloads/20040028027.pdf
    year: 2004
    kind: report
    license: public domain (NASA)
  nasa-2002:
    title: 'NASA/TM-2002-211718: Preliminary Study on Fatigue Strengths of Fretted Ti-48Al-2Cr-2Nb'
    id: NASA TM 2002-211718, Miyoshi, Lerch and Draper
    url: https://ntrs.nasa.gov/api/citations/20020081267/downloads/20020081267.pdf
    year: 2002
    kind: report
    license: public domain (NASA)
  gaa-1992:
    title: Titanium Aluminides for Aerospace Applications
    id: Chesnutt, J.C., Superalloys 1992, TMS, pp. 381-389
    url: https://www.tms.org/Superalloys/10.7449/1992/Superalloys_1992_381_389.pdf
    year: 1992
    kind: paper
    license: TMS conference paper, cited not reproduced
  wiki-tial:
    title: Titanium aluminide (Wikipedia)
    id: Wikipedia, Titanium aluminide
    url: https://en.wikipedia.org/wiki/Titanium_aluminide
    year: 2026
    kind: web
    license: CC BY-SA 4.0
  ge-leap-avio:
    title: A LEAP for Avio Aero (GE Aerospace article)
    id: GE Aerospace news article
    url: https://www.geaerospace.com/news/articles/product/leap-avio-aero
    year: 2026
    kind: web
    license: manufacturer web page, cited not reproduced
  pubchem-ti:
    title: 'PubChem: Titanium (CID 23963), GHS classification and DOT summary'
    id: PubChem CID 23963
    url: https://pubchem.ncbi.nlm.nih.gov/compound/23963
    year: 2026
    kind: database
    license: PubChem, public
  pubchem-al:
    title: 'PubChem: Aluminum (CID 5359268), GHS classification'
    id: PubChem CID 5359268
    url: https://pubchem.ncbi.nlm.nih.gov/compound/5359268
    year: 2026
    kind: database
    license: PubChem, public
  usgs-ti-2026:
    title: 'Mineral Commodity Summaries 2026: Titanium (USGS, February 2026)'
    id: USGS MCS 2026, Titanium
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-titanium.pdf
    year: 2026
    kind: report
    license: US Government work, public domain
  usgs-al-2026:
    title: 'Mineral Commodity Summaries 2026: Aluminum (USGS, February 2026)'
    id: USGS MCS 2026, Aluminum
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-aluminum.pdf
    year: 2026
    kind: report
    license: US Government work, public domain
  usgs-cr-2026:
    title: 'Mineral Commodity Summaries 2026: Chromium (USGS, February 2026)'
    id: USGS MCS 2026, Chromium
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
    year: 2026
    kind: report
    license: US Government work, public domain
  usgs-nb-2026:
    title: 'Mineral Commodity Summaries 2026: Niobium (USGS, February 2026)'
    id: USGS MCS 2026, Niobium
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-niobium.pdf
    year: 2026
    kind: report
    license: US Government work, public domain
  usgs-crit2025:
    title: About the 2025 List of Critical Minerals (USGS)
    id: Final 2025 List of Critical Minerals, November 2025
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 22
  unreachable: 1
  caveats: 4
  note: Written 2026-10-26 by an assistant from pages read in this run. Gamma TiAl composition, Ti-48-2-2 tensile and modulus values, and class densities and oxidation limits come from NASA and GE sources. Supply shares are computed from USGS tonnage. The OSTI oxidation abstract was unreachable.
story:
  recipe:
    line: Gamma TiAl is an intermetallic compound of titanium and aluminium. The turbine-blade alloy Ti-48Al-2Cr-2Nb (at. %) is cast, and NASA describes its microstructure as duplex, with gamma grains and gamma plus alpha-2 lamellar colonies. Alpha-2 Ti3Al is a separate class based on a hexagonal D019 structure.
    parts:
      - name: Titanium
        symbol: Ti
        share: balance
        role: Base metal. Titanium makes up the rest of the alloy after the other elements.
        source: nasa-2004
        where: Introduction, Ti-48Al-2Cr-2Nb (at.%); balance is implied by the nominal composition
        share_note: balance (the rest)
      - name: Aluminium
        symbol: Al
        share_percent: 48
        share_note: at. %, nominal
        role: Main alloying element. The cast-to-size samples measured 47.5 at. % Al, and a slightly lower Al level gave higher room-temperature yield strength in NASA's test.
        source: nasa-2004
        where: Introduction, Ti-48Al-2Cr-2Nb (at.%); Materials, chemistry paragraph
      - name: Chromium
        symbol: Cr
        share_percent: 2
        share_note: at. %, nominal
        role: Alloying addition. In the cited oxidation comparison, Cr and Nb additions raised oxidation resistance over binary TiAl.
        source: nasa-2004
        where: Introduction, Ti-48Al-2Cr-2Nb (at.%)
      - name: Niobium
        symbol: Nb
        share_percent: 2
        share_note: at. %, nominal
        role: Alloying addition for strength and oxidation resistance.
        source: nasa-2004
        where: Introduction, Ti-48Al-2Cr-2Nb (at.%)
  risk_groups:
    - title: For people
      level: 0
      verdict: Solid alloy not classified; powder and swarf are flammable
      lead: 'The solid alloy has no hazard class in the sources read. The powder is the concern: PubChem gives titanium and aluminum powders flammable-solid and related classes.'
      points:
        - label: Solid alloy
          line: PubChem reports titanium as not meeting GHS hazard criteria in 606 of 808 company reports. The NASA and GE sources give no hazard class for the alloy.
        - label: Powder and swarf
          line: Titanium powder carries H228, H250 and H251 in PubChem. Aluminum powder carries H250, H261 and H228. Treat both as fire hazards and keep them away from air and water.
    - title: Shipping
      lead: Titanium powder is a regulated shipping item in the United States.
      points:
        - label: Wetted powder
          line: The DOT summary lists titanium powder wetted with not less than 25 percent water, with a visible excess of water present, for mechanically produced particles under 53 microns.
  why: Gamma TiAl is a light intermetallic for hot rotating parts. NASA gives its density as 3.8 g/cm3 for the family and calls its low density, together with good high-temperature properties, the reason it is a candidate for turbine machinery. GE built low-pressure turbine blades from Ti-48Al-2Cr-2Nb and engine tested them in 1993. Its main weakness is low ductility at room temperature, which made impact resistance the central question in NASA's program.
  uses:
    - where: GEnx engine
      line: GE uses gamma TiAl for the low-pressure turbine blades on its GEnx engine, which powers the Boeing 787 and 747-8 and entered service in 2011.
    - where: LEAP engine
      line: GE Aerospace lists the titanium aluminide low-pressure turbine blades among the LEAP engine's state-of-the-art technologies and materials. LEAP is built by CFM International.
    - where: Engine test, 1993
      line: GE Aircraft Engines engine-tested Ti-48Al-2Cr-2Nb low-pressure turbine blades in 1993. NASA then funded a team to optimise the design for commercial service.
  can_do:
    - label: Density
      benchmark: density
      line: NASA gives the density of the gamma TiAl family as 3.8 g/cm3. The GE review gives 4.04 g/cm3 for the gamma class, against 4.54 g/cm3 for titanium alloys and 8.3 g/cm3 for superalloys.
    - label: Strength
      benchmark: yield_strength
      line: Cast Ti-48-2-2 has a 0.2 % offset yield strength of 326 MPa at 23 degC and 284 MPa at 650 degC, with tensile strengths of 422 MPa and 474 MPa.
    - label: Stiffness
      benchmark: elastic_modulus
      line: Cast Ti-48-2-2 has an elastic modulus of 168 GPa at 23 degC and 141 GPa at 650 degC. The gamma class is listed at 176 GPa, above the 110 GPa of titanium alloys in the same GE table.
    - label: Temperature
      benchmark: max_oxidation_temperature
      line: The GE table gives an oxidation limit of 815 degC for the gamma class, and a creep limit of 900 degC. The best GE gamma alloys held 550 MPa at 760 degC.
  compare: In the GE comparison, gamma TiAl is lighter than titanium alloys and far lighter than superalloys, and it is stiffer than titanium alloys. It has much less room-temperature ductility than conventional titanium alloys and is more sensitive to impact. The alpha-2 class is denser at 4.84 g/cm3 and has a lower oxidation limit of 705 degC.
  compare_rows:
    - label: Density
      benchmark: density
    - label: Elastic modulus
      benchmark: elastic_modulus
    - label: Yield strength
      benchmark: yield_strength
  handling:
    - 'Powder and swarf: PubChem gives H228, H250 and H251 for titanium. Keep powder dry, away from air and heat, and away from ignition sources.'
    - 'Shipping: the DOT entry for titanium powder requires it to be wetted with at least 25 percent water.'
    - 'Blades and specimens: the NASA work used cast-to-size and cast overstock parts, and the sources read give no heat-treatment window.'
  good_for:
    - Lightweight hot rotating parts. The family density is 3.8 g/cm3, and cast Ti-48-2-2 holds 474 MPa tensile strength at 650 degC.
    - Stiffness and oxidation. The gamma class is listed at 176 GPa and an oxidation limit of 815 degC.
  watch_out:
    - 'Room-temperature ductility: cast Ti-48-2-2 elongates 1.70 % at 23 degC.'
    - Impact damage can crack thin sections and, at high energy, remove material in a blowout.
    - Properties depend on Al content and microstructure. NASA found that 47.1 at. % Al gave higher room-temperature yield strength than 48 at. %.
    - The alpha-2 class is denser at 4.84 g/cm3 and has a lower oxidation limit of 705 degC.
  verdict: Gamma TiAl is a stiff, light, heat-tolerant intermetallic that GE has used in engine turbines, most recently in the GEnx and LEAP. Its low ductility and sensitivity to impact are the main limits. The sources read here give no space, seawater or hydrogen data.