Superalloys

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Nickel base superalloys

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Superalloys

  1. 1. SUPERALLOYSSUPERALLOYSN. PRAKASANME METALLURGY
  2. 2. SUPERALLOYSSUPERALLOYSINTRODUCTION Nickel-based superalloys possess goodcombinations of high-temperature mechanicalproperties and oxidation resistance up toapproximately 550°C. High temperature heat-resistance alloys, which canretain high strengths at elevated temperatures. Alloying increases the strength and temperaturecapability but reduces the processability.
  3. 3. SUPERALLOYSSUPERALLOYSPROPERTIESHeat resistant and high strength at hightemperature (760-980oC).Good corrosion resistance.Good oxidation resistance.High toughness and ductilityExcellent cryogenic temperature properties.
  4. 4. SUPERALLOYSSUPERALLOYSCLASSIFICATIONThere are three types of Ni-base superalloys:• Nickel base,• Nicke-lron base,• Cobalt base.The alloys contain high Cr with Ti, Al to fromprecipitates and additions of Mo, Co, Nb, Zr, B,Fe.
  5. 5. SUPERALLOYSSUPERALLOYSMICROSTRUCTUREThe major phases present in the nickel-basesuperalloys:γ (gamma) phase – the continuous matrix ofFCC austenite.γ’ (gamma prime) phase – the majorprecipitate phase (more cubic shape).Carbides –various types, mainly M23C6 andMC. (M = metal).
  6. 6. Three strengthening mechanismsare used in Ni superalloys:· Solid solution hardening· Coherent precipitatehardening· Carbide phases on grainboundariesSTRENGTHENING MECHANISMSTRENGTHENING MECHANISMSUPERALLOYSSUPERALLOYS
  7. 7. SUPERALLOYSSUPERALLOYSSolid solution strengthening• Cr, Mo, Al, Nb, Ti and othersPrecipitation strengthening• Mostly due to Al and Ti• Ni3(Al,Ti), gamma primeCarbide phases• M23C6, M6C or MCSTRENGTHENING MECHANISMSTRENGTHENING MECHANISM
  8. 8. SUPERALLOYSSUPERALLOYSMICROSTRUCTUREMICROSTRUCTURE
  9. 9. SUPERALLOYSSUPERALLOYSMICROSTRUCTUREA two-phase equilibrium microstructure isgenerated, consisting of gamma γ and gamma-prime (γ´)Both phases are face-centered-cubic, havealmost identical lattice dimensions and alsosimilar orientation. Consequently the twophases are almost coherent.The lattice sites in the γ-phase are totallyequivalent and the atoms constituting the solidsolution being distributed randomly.
  10. 10. MICROSTRUCTUREMICROSTRUCTUREIn the γ´-phase (Ni3(Al,Ti) ) the nickel atomsare at the face-centers and the aluminium ortitanium atoms at the cube corners.• The close match in matrix/precipitate latticeparameter (~0-1%) combined with thechemical compatibility allows the γ´ toprecipitate homogeneously throughout thematrix and has a long-time stability.SUPERALLOYSSUPERALLOYS
  11. 11. MICROSTRUCTUREMICROSTRUCTURE Carbides The added content of carbon is approximately 0.05-0.2%. In combination with reactive and refractory elementssuch as titanium, tantalum, and hafnium it formscarbides (e.g., TiC, TaC, or HfC). During heat treatment these carbides begin todecompose and forms lower carbides such as M23C6and M6C, which tend to generate on the grainboundaries. The mainly M elements in M23C6 are chromium, iron,tungsten and molybdenum.SUPERALLOYSSUPERALLOYS
  12. 12. EFFECT OF ALLOYING ELEMENTSEFFECT OF ALLOYING ELEMENTSSUPERALLOYSSUPERALLOYS
  13. 13. SUPERALLOYSSUPERALLOYSCHEMICAL COMPOSITIONMost nickel-based alloys contain 10-20% Cr,up to 8% Al and Ti, 5-10% Co, and smallamounts of B, Zr, and C.Chromium and aluminium are necessary foroxidation resistance.The elements such as C, Cr, Mo, W, C, Nb,Ta, Ti and Hf form carbides.
  14. 14. SUPERALLOYSSUPERALLOYSCHEMICAL COMPOSITIONElements which stabilize the grain boundaryare B, C, and Zr. Their atomic diameters differfrom Ni by 21-27%. The resulting reduction ingrain boundary energy is associated withbetter creep strength and ductility.The elements Co, Fe, Cr, Nb, Ta, Mo, W, V, Tiand Al are also solid-solution strengtheners,both in γ and γ phase.
  15. 15. SUPERALLOYSSUPERALLOYSNi-Iron SuperalloysFe is added to replace some of Ni as it haslower cost.Ni-Fe superalloys contains 25-45%Ni and 15-60%Fe.Microstructure consists of austenistic FCCmatrix and can be strengthened by solidsolution strengthening (Mo, Cr), andprecipitation hardening (Ti, Nb, Al) by formingintermetallic phases.Examples: Inconel 707, 718, 901.
  16. 16. SUPERALLOYSSUPERALLOYSSUPERALLOY GRADES
  17. 17. Applications: Aerospace Gas Turbine Engines Space vehicles - Rocket engines, Nuclear reactors Power Generation Turbines Submarines. Petrochemical equipment. High-Temperature Fasteners Combustion Engine Exhaust Valves Hot Working Tooling and Dies,SUPERALLOYSSUPERALLOYS
  18. 18. SUPERALLOYSSUPERALLOYS
  19. 19. REQUIREMENTS FOR COMBUSTION ZONETURBINE BLADESSUPERALLOYSSUPERALLOYS
  20. 20. NI BASE SUPERALLOY TURBINE BLADENI BASE SUPERALLOY TURBINE BLADE
  21. 21. REFERENCES: Henkel and Pense, Structure and Properties ofEngineering materials, 5thedition. Loren A. Jacobson, Physical Metallurgy_class notes Prof. Diego Colombo, Nickel-based superalloys andtheir application in the aircraft industry. Hiroshi Harada and Yuefeng GU, High temperaturematerialsSUPERALLOYSSUPERALLOYS

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