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Strength of Energy Engineering Materials

Strength of Energy Engineering Materials. Abdel-Fatah M HASHEM Professor of materials science South Valley University, EGYPT. April 2009, Japan. Collaborative Research Centre SFB 651 at the AU and SVU. Turbines Fluid dynamics Phys. chemistry Metal physics Materials Casting Coating

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Strength of Energy Engineering Materials

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  1. Strength of Energy Engineering Materials Abdel-Fatah M HASHEM Professor of materials science South Valley University, EGYPT April 2009, Japan

  2. Collaborative Research Centre SFB 651 at the AU and SVU

  3. Turbines Fluid dynamics Phys. chemistry Metal physics Materials Casting Coating Welding Metal forming Laser techn. 12 years 15 Professors and their co- workers 20 Million € =150 Million Egypt. pounds

  4. Inlet Temperature of Gas turbines: from 1230 °C to 1320 °C

  5. Inlet Temperature of Steam Turbines: from 600 °C to 700 °C Steam turbine (Siemens) E911 <1990 560 °C 12% Cr, 1% Mo (X20CrMoV12-1) >1990 600 °C 9% Cr-Steels P91 +0% W E911 +1% W P92: +2% W >2000 625 °C NF12: 12% Cr, 3% W, 3% Co Goal 700 °C Nickel-Base-Alloys

  6. Steam Turbine: Increase of efficiency X20CrMoV12-1 12C1Mo-V P91: 9Cr-1Mo-VNb E911 X12CrMoWVNbN10-1-1 P92 (NF616) 9Cr-0,5Mo-1.8W-V-Nb NF12: 12Cr-2.6W-2.5Co-0.5Ni-V-Nb

  7. Steam Turbine: Cooling system

  8. Laboratory experiments Reality: Multi-axial stress state with stress components varying with time Data available: Uni-axial experiments with simple time functions Therefore, Modelling is essential

  9. Influence of Temperature on the Stress strain Curve 200 °C - 700 °C Intercrystalline damage >700 °C Dynamic recrystallisation 23 °C – 150 °C Dynamic recovery 200 °C - 300 °C Intercrystalline damage

  10. Flow curve: Description and Influence of strain rate Power law ?

  11. Creep curves and creep rate curves

  12. Minimum creep rate as stress function and creep fracture curve Up to 10000 h University laboratory Up to 200000 h Industry, Standards

  13. Proof stress and creep strength as Loading limits Design limits: with a factor of safety of 1.5 1. Low Temperatures: 0,2% Proof Stress 2. High Temperatures: Creep Strength= Stress for a fracture time of 100000 h Maximum service temperature: Creep strength for 100000 h = 100 MPa

  14. Increase of creep strength 1. Reducing grain boundary area per unit volume Coarce grains Directional Single solidification crystals

  15. Increase of creep strength 2. Precipitation hardening Barriers for the dislocation Influence of nitrides 0.05 m% N [Abe, F.: Sol.State.Phys. 8(2004)305 ]

  16. Increase of creep strength 3. Reinforcement by continuous fibres Not for cyclic compression !

  17. s a P M 1 0 0 , s s e t S k c s a i B d 5 0 5 0 n a d e i l p p X 6 C r N i 1 8 - 1 1 A 6 9 0 ° C 0 0 0 2 4 6 8 T i m e , h Creep under stresses and temperatures varying with time The Creep rate depends on the effective stress i.e. on the difference between Applied stress and internal back stress 1 0 0 s s i X 6 C r N i 1 8 - 1 1 6 9 0 ° C 0 2 4 6 8 T i m e , h

  18. Concept of the internal back stress

  19. Internal back stress

  20. Cyclic creep: Life assessment • L= 0.6 under pulsating stress • L= 0.8 under pulsating Temperature

  21. Stress Relaxation: Basic equation • Creep strain increases with time • Total strain remains constant • The elastic strain decreases • Stress decreases with time

  22. Stress relaxation curves Nickel-base alloy: Crystalline order changes around 550°C increases the specific volume And hence reduces relaxation

  23. Low Cycle Fatigue: Modelling

  24. Low Cycle Fatigue: Life assessment Number of cycles at fracture

  25. Voids: Growth by diffusion and by creep deformation Void growth by Diffusion Void growth by creep deformation of the surrounding materials

  26. Wedge type micro-cracks 61000 Cracks in X6CrNiMoNb16-16 50000 Cracks in X6CrNi18-11

  27. Material: Ni-based superalloy

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