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

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Collaborative Research Centre SFB 651 at the AU and SVU

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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

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

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

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Steam Turbine: Increase of efficiency X20CrMoV12-112C1Mo-V P91: 9Cr-1Mo-VNb E911X12CrMoWVNbN P92 (NF616) 9Cr-0,5Mo-1.8W-V-Nb NF12: 12Cr-2.6W-2.5Co-0.5Ni-V-Nb

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Steam Turbine: Cooling system

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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

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

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

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Creep curves and creep rate curves

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

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

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

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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 ]

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

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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 X6CrNi °C i Time, h

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Concept of the internal back stress

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Internal back stress

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

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

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

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Low Cycle Fatigue: Modelling

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Low Cycle Fatigue: Life assessment Number of cycles at fracture

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

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Wedge type micro-cracks Cracks in X6CrNiMoNb Cracks in X6CrNi18-11

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Material: Ni-based superalloy

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Thank you for your attention

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