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Grain Boundaries

Grain Boundaries

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Grain Boundaries

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  1. Ni-Base Superalloy Waspalloy low-angle grain boundary 50µm Grain Boundaries high-angle grain boundary (Q>15°)

  2. Properties of Materials • Mechanical Properties • Elastic • Plastic • Viscoelastic • Creep • Testing methods

  3. stress s=F/A strain e=l-l0/l0 The Tensile Test

  4. The Tensile Test

  5. Force=dE/dr r0 Elastic Deformation distance r

  6. Elastic constants (isotropic case) • Stress – strain / shear stress – shear strain • Young’s modulus • Shear modulus • Poisson ratio • In order to completely describe the elastic behavior of a solid 2 of these constants need to be known!

  7. sY sY Yield Strength sY yield-point phenomenon (C steels, dislocations are pinned by C) 0.002 strain offset

  8. true stress engineering stress The Stress-Strain Curve stress necking strain

  9. Materials Selection Charts Strength [MPa] Density [1000kg/m³]

  10. shear stress t Plastic Deformation – Dislocation Glide

  11. Plastic Deformation – Dislocation Glide =>macroscopic deformation

  12. Plastic Deformation – Dislocation Glide dislocation motion

  13. Plastic Deformation shear stress t

  14. Some concluding words on dislocations • Strengthening mechanisms • Grain size reduction (Hall-Petch equation) • Solid solution strengthening • Strain hardening

  15. Mechanical testing • Hardness • Vickers • Rockwell • … Nanoindentation • Ductility • Toughness • Creep • Fatigue

  16. length of the diagonals d1 and d2 Vickers Microhardness Testing

  17. Rockwell Hardness Testing (HRC) scale indenter (120° diamond pyramid) specimen

  18. %RA, percent reduction in area ductile brittle %EL, percent elongation Ductility stress strain

  19. Charpy Impact Testing impact energy Av=mg(h-h´) specific ak=Av/A0 hammer (DIN 50115)

  20. BDTT T-Dependence of Av

  21. Cleavage Fracture at Low Temperatures

  22. e Deformation at Elevated Temperatures: Creep

  23. de/dt Creep Testing

  24. Fatigue Loading during Service

  25. Fatigue Testing

  26. Fatigue Testing rotating-bending push-pull load counter servohydraulic actuator

  27. total life design fatigue limit Fatigue-Testing: The S/N Diagram stress amplitude [MPa] cycles to failure N

  28. Fracture Mechanics KIc represents resistance to brittle fracture [MPam0.5]

  29. force extensometer displacement Determination of KIc using Compact Tension (CT specimens)