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An affordable creep-resistant nickel-base alloy for power plant

Franck Tancret. Harry Bhadeshia. An affordable creep-resistant nickel-base alloy for power plant. The problem. Future power plant: 750°C. New steels: 650°C. => Use of Ni-base alloys. But: Commercial superalloys are too expensive (Nb, Ta, Co, Mo…).

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An affordable creep-resistant nickel-base alloy for power plant

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  1. Franck Tancret Harry Bhadeshia An affordable creep-resistant nickel-base alloy for power plant

  2. The problem Future power plant: 750°C New steels: 650°C => Use of Ni-base alloys But: Commercial superalloys are too expensive (Nb, Ta, Co, Mo…) => Design an affordable creep-resistant Ni-base alloy

  3. Industrial requirements • Affordable • 100 000 h creep lifetime under 100 MPa at 750°C • Stable at service temperature • Forgeable • Weldable • Corrosion resistance • Toughness

  4. Design procedure • Empirical nonlinear multiparametric modelling of mechanical properties as a function of composition and processing conditions (Gaussian processes) • Based on a huge database on the properties of many existing alloys => captures trends and interactions • Phase diagram and segregation simulation (Thermo-Calc) • Processability • General metallurgy principles Ni – 20Cr – 3.5 W – 2.3 Al – 2.1 Ti – 5 Fe – 0.4 Si – 0.07 C – 0.005 B Materials Science & Technology, 19 (2003)

  5. Experimental results

  6. Next issue: PROCESSING • Melting and solidification (primary chemical segregation) • Forging (g’-free temperature window) • Heat treatment (precipiation hardening…) • Welding • How modelling can be used to address these issues? • Is the designed alloy easy to process?

  7. melting forging window No undesirable phases at service temperature Phase diagram simulation (Thermo-Calc)

  8. T = T – 1 K DV and composition LIQUID SOLID(S) Primary segregation simulation (Thermo-Calc) • Scheil’s approximation: • homogeneous liquid • diffusion-free solids LIQUID

  9. cylinder sphere plate Primary segregation simulation (Thermo-Calc) Simple dendrite geometrical models => composition profiles

  10. Primary segregation simulation (Thermo-Calc) EDS analysis profile

  11. Primary segregation simulation (Thermo-Calc)

  12. Solutionising 1175°C, WQ Isothermal heat treatments below g’ solvus, WQ Vickers hardness Precipitation hardening kinetics

  13. During ageing: g / g’ Precipitation hardening kinetics Diffusion-controlled growth model: 3 Ni + diffusing (Al, Ti) => Ni3(Al,Ti) Cav Before ageing: solutionised g

  14. distance from precipitate C(1) = Ceq C(2) … C(i-1) C(i) C(i+1) … dNp dN(i-1) dN(i) surface S g / g’ interface adjustable parameter Precipitation hardening kinetics Diffusion-controlled growth model (Al + Ti)

  15. C C C Cav Cav Cav t t = 0 Ceq Ceq Ceq d d d t =  Precipitation hardening kinetics Diffusion-controlled growth model (Al + Ti)

  16. Precipitation hardening kinetics Diffusion-controlled growth model (Al + Ti)

  17. Precipitation hardening kinetics Diffusion-controlled growth model (Al + Ti)

  18. CONCLUSIONS • Design of an affordable Ni-base alloy for power-plant • 100 000 h creep lifetime under 100 MPa at 750°C • Corrosion-resistant, stable, forgeable, weldable… • Extensive use of modelling: • Mechanical properties (Gaussian processes) • Phase diagram simulation • Stability • Forgeability • Weldability • Age-hardening • Solidification segregation (Scheil’s model) • Precipitation-hardening kinetics (diffusion model)

  19. Present and future work • Multicomponent diffusion growth model • Welding • High temperature ductility / forgeability / recrystallisation… • Corrosion-resistance

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