Titane Alliages d'aluminium

Table des matières

Vue d'ensemble

Titane Alliages d'aluminium are a class of metallic materials that contain a mixture of titanium and aluminum. They are lightweight, have high strength, and excellent corrosion and oxidation resistance at high temperatures.

TiAl alloys are considered an important high-temperature structural material for aerospace and automotive applications due to their unique combination of properties. Their low density makes them lighter than nickel-based superalloys, while still retaining strength and stability at temperatures up to 750°C.

Propriétés clés de Titane Alliages d'aluminium

PropriétéDescription
Densité3.7 – 4.1 g/cm3, much lower than nickel alloys
La forceRetain high strength at temperatures up to 750°C
RigiditéHigh elastic modulus of about 160 GPa
DuctilitéBrittle at room temperature but becomes more ductile at high temperatures
Résistance à la corrosionExcellent corrosion resistance due to presence of titanium
Résistance à l'oxydationForm protective oxide layer resulting in good oxidation resistance up to 750°C
CoûtMore expensive than titanium alloys but cheaper than nickel alloys
titanium aluminum alloy

Types of Titanium Aluminum Alloys

There are two primary types of titanium aluminum alloys:

Gamma TiAl Alloys

Gamma TiAl alloys have a lamellar microstructure and contain about 45-48% titanium, with the remainder aluminum. Small additions of elements like niobium, carbon, boron and chromium are also made to enhance properties.

The gamma phase TiAl alloys offer a good balance of low density, strength, ductility and oxidation resistance. They are the most widely used TiAl alloys.

Alpha-2 Ti3Al Alloys

Alpha-2 Ti3Al alloys contain about 25% aluminum and have a hexagonal crystal structure. They offer very high tensile strength but have lower ductility and fracture toughness compared to gamma TiAl alloys.

Alpha-2 alloys are typically used in very high temperature applications above 800°C such as in turbochargers.

Composition des Titane Alliages d'aluminium

Titanium aluminum alloys contain titanium as the major component, with aluminum and small amounts of other elements. Here is the typical composition range:

Alloy ElementGamme de compositionRôle
Titane (Ti)52-56%Primary base element
Aluminium (Al)44-48%Main alloying element with Ti
Niobium (Nb)Jusqu'à 2%Increases strength and creep resistance
Chrome (Cr)Jusqu'à 2%Increases oxidation resistance
Bore (B)Up to 0.2%Improves ductility
Carbone (C)Jusqu'à 0,1%Increases strength
Silicium (Si)0.1-1%Improves oxidation resistance
Tungstène (W)0.1-1%Refines grain size
Molybdène (Mo)0.1-1%Increases strength

The percentages of alloying elements are precisely controlled to achieve the right microstructure and properties in the alloy.

Key Properties of Titanium Aluminum Alloys

Titanium Aluminum Alloy Strength Properties

PropriétéValeurDescription
Résistance à la traction500 – 1100 MPaVery high strength compared to titanium alloys
Limite d'élasticité (décalage de 0,2%)400 – 1000 MPaMeasure of elastic strength in alloy
Résistance à la compression600 – 1500 MPaExcellent compressive strength
Résistance au fluage100 – 350 MPaAbility to withstand loads at high temperatures
Résistance à la rupture15 – 35 MPa√mResistance to crack propagation is lower than nickel alloys

Propriétés physiques

PropriétéValeur
Densité3.7 – 4.1 g/cm3
Point de fusion1360°C – 1460°C
Conductivité thermique6 – 25 W/mK
Résistivité électrique150 – 250 μΩ.cm
Coefficient de dilatation thermique11 – 13 x 10<sup>-6</sup> /K

Propriétés mécaniques à température ambiante

PropriétéValeurDescription
Dureté300 – 400 HVMeasure of resistance to indentation
Module de Young150 – 160 GPaMeasure of stiffness
Module de cisaillement60 – 65 GPaMeasure of rigidity
Rapport de Poisson0.25 – 0.34Ratio relating strain in directions perpendicular and parallel to applied load
UsinabilitéDifficileChallenging to machine compared to steels

Applications et utilisations de Titane Alliages d'aluminium

Titanium aluminum alloys are used in wide range of high performance engineering applications. Some key uses are:

Uses in Aerospace Industry

  • Aircraft engine components like blades, discs, air inlet cowls
  • Airframe and wing structures in high-speed aircraft
  • Space vehicle parts due to combination of low weight and temperature resistance

Automotive Industry Uses

  • Roues et carters de turbine de turbocompresseur
  • Connecting rods, valves, springs and fasteners in high performance engines
  • Motorsport components like conrods and valves

Autres applications

  • Gas turbine engine parts, power generation and marine applications
  • Biomedical implants like artificial hip joints
  • Sporting goods like bicycle frames, golf clubs

Here is a comparison of the use of titanium aluminum alloys versus alternatives:

ApplicationTiAl AlloysAlternative Materials
Aircraft Engines✅ Excellent strength-to-weight ratio up to 750°C makes it suitable for blades, vanes, shaftsNickel superalloys have higher temperature capability but are heavier
Automotive Turbochargers✅ Good balance of high strength, temperature resistance and lower density than nickel alloysNickel alloys can withstand higher peak temperatures
Cellules d'avion✅ 20-35% lighter than titanium alloys with equivalent strength for plane wings, tails and fuselageTitanium alloys offer higher fracture toughness
Implants biomédicaux✅ Contains titanium which allows natural bonding to human boneStainless steel, cobalt chrome alloys also commonly used

Normes et spécifications de l'industrie

Some widely used industry standards for titanium aluminum alloys are:

StandardDescription
AMS 4928Standard specification for gamma titanium aluminide alloy sheet, strip and plate
AMS 4965Standard for gamma titanium aluminide alloys processed by powder metallurgy
AMS 4972Standard specification for alpha-beta or beta titanium aluminides bars, rods and wire
ISO 21365Specification for structural gamma TiAl alloys
ASTM B381Standard classification for titanium-aluminum-vanadium alloys for surgical implants

Alloy products are offered in variety of grades that meet different standards for chemistry, microstructure, and mechanical properties.

Some common titanium aluminum grades are:

  • Ti-48Al-2W-0.5Si (AMS 4928)
  • Ti-47Al-2Cr-2Nb (ISO 21365 Grade 5)
  • Ti-45Al-5Nb-0.2C-0.2B (AMS 4965 Grade 5)

Fournisseurs et coûts

Some leading global suppliers of titanium aluminum alloys include:

FournisseurAnnées d'études proposéesMéthodes de production
VSMPOTi-47Al-2Cr-2Nb<br>Ti-48Al-2Cr-2Nb-1Ta-0.7WCoulée en cire perdue<br>Forgeage
ATITi-48Al-2W-0.5Si<br>Ti-47Al-2Cr-2NbPrecision casting<br>Métallurgie des poudres
Precision Castparts CorpAlliages sur mesureCoulée en cire perdue
PlanseeTiAl gamma alloysMétallurgie des poudres

Titanium aluminum alloys are more expensive than titanium alloys but cheaper than nickel-based superalloys. Some typical pricing estimates are:

GradeEstimation des prix
Ti-48Al-2Cr-2Nb$85 – $125 per kg
Ti-47Al-2W-0.5Si$100 - $150 par kg
Custom TiAl alloys$150 – $250 per kg

Pricing varies based on order volume, size specifications, certification requirements and other customizations.

Advantages and Limitations of Titanium Aluminum Alloys

Avantages et bénéfices

  • Very high specific strength – high strength-to-weight ratio
  • Excellent strength retention up to 750°C
  • Good environmental resistance – oxidation, burning and corrosion
  • Lower cost than nickel and cobalt superalloys
  • Some hot workability for forging, rolling

Shortcomings and Limitations

  • Processing difficulties – hot working as well as machining
  • Brittle behavior at room temperature
  • Relatively low fracture toughness
  • Maximum use temperature limited to 750°C
  • Subject to hydrogen and moisture absorption

Here is a comparison of the advantages and disadvantages relative to alternatives:

ParamètresTiAl AlloysSuperalliages de nickelAlliages de titane
Résistance à haute températureBon jusqu'à 750°C✅ Excellent above 900°CMédiocre au-dessus de 500°C
Densité✅ LowestPlus élevéComparable
Résistance à l'oxydationBon jusqu'à 750°C✅ Best above 800°CPoor above 550°C
Coût✅ LowerLe plus élevéPlus élevé
Aptitude au travailPauvreBon✅ Best
Tolérance aux dommagesPauvreBon✅ Excellent
titanium aluminum alloy

FAQ

Q: What are gamma titanium aluminides?

A: Gamma TiAl aluminides are intermetallic alloys containing titanium (Ti) and aluminum (Al) with a gamma (γ) phase crystal structure. They have an ordered lamellar arrangement of Ti and Al atoms. Gamma TiAl is the most commonly used alloy type.

Q: Why are TiAl alloys considered for aerospace applications?

A: TiAl alloys offer an excellent combination of low density and good mechanical properties up to 750°C. This allows lighter and more efficient aero-engine components to be designed using TiAl instead of much heavier nickel alloys.

Q: What are some examples of TiAl turbocharger components?

A: TiAl alloys are increasingly used to make turbocharger wheels and housings in high performance diesel and gasoline car engines. The low density and temperature resistance provide higher power density and efficiency.

Q: What are the main challenges in using TiAl alloys?

A: Difficulty in processing via casting, forging and machining along with intrinsic brittleness at room temperature, and lower damage tolerance than competing alloys creates barriers for adoption. However, processing methods and alloy development continue to advance.

Q: What is the typical oxygen content limit for TiAl alloys?

A: Oxygen is limited to less than 0.2% in TiAl alloys. Higher oxygen levels negatively impact ductility. Advanced melting and casting methods are used to control oxygen pickup.

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