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

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Presentation transcript:

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 Welding Metal forming Laser techn. 12 years 15 Professors and their co- workers 20 Million € =150 Million Egypt. pounds

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

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

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

Steam Turbine: Cooling system

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

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

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

Creep curves and creep rate curves

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

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

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

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 ]

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

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

Concept of the internal back stress

Internal back stress

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

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

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

Low Cycle Fatigue: Modelling

Low Cycle Fatigue: Life assessment Number of cycles at fracture

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

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

Material: Ni-based superalloy

Thank you for your attention