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

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

14. 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

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

17. Inlet Temperature of Steam Turbines: from 600 °C to 700 °C Steam turbine (Siemens) <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 E911

18. Steam Turbine: Increase of efficiency X20CrMoV12-112C1Mo-V P91: 9Cr-1Mo-VNb E911X12CrMoWVNbN10-1-1 P92 (NF616) 9Cr-0,5Mo-1.8W-V-Nb NF12: 12Cr-2.6W-2.5Co-0.5Ni-V-Nb

19. Steam Turbine: Cooling system

20. 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

21. 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

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

23. Creep curves and creep rate curves

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

25. 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

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

27. 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 ]

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

29. 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 100 02468 X6CrNi18-11 690 °C  i  Time, h

30. Concept of the internal back stress

31. Internal back stress

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

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

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

35. Low Cycle Fatigue: Modelling

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

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

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

39. Material: Ni-based superalloy

61. Thank you for your attention