1. casting class1

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1. casting class1

  1. 1. Some casting-products (casting) A simple casting technique
  2. 2. Microstructure: behind the desired Properties of the product material Phases Grains various crystals structures Grain boundary unit cell atomic bonding
  3. 3. Example:Ti Atomic number: 22 Phase: solid Crystal structure: Hexagonal Atomic radious: 140pm Electronic configuration: 1S22S22P63S23P63d24S2 Type: transitional metal Can be alloyed with: Fe (grain refinement) Al (grain refinement) Cu (hardening)
  4. 4. Structure of matter Atomic bonding: depending on electronic configuration Attractive force Force between two atoms repulsive force de Bonds: # Primary bonds: Ionic Covalent #Second~ bonds: van der Waals force Metallic
  5. 5. Metallic covalent ionic
  6. 6. Dipole force Hydrogen bonding van der Waals forces
  7. 7. Unit cells Crystalline structure BCC FCC Allotropic characteristics? HCP
  8. 8. Imperfections in crystals Point defect ► point defect ► line defect ► surface defect
  9. 9. Line defect
  10. 10. Deformation in metallic crystal • Elastic deformation • Plastic deformation Plastic deformation mechanism: • slip : slip, slip plane and slip direction • twinning: twinning plane • combination of both
  11. 11. Grain, grain size and grain boundary Grain: Individual crystals: array of repeating lattice Grain boundary: Growing crystals at random position and orientation interfere ultimately and form a surface defect at their interface. known as grain boundary Grain size: Finer structure indicates in general higher strength. Larger grain boundaries ensures locking of the movement of dislocations in crystals under deformation, thus increasing strength of the material---- strain hardening
  12. 12. Engineering Materials Metals: • Almost all have the crystalline structures: FCC, BCC, HCP are common • Atoms are held together by metallic bonding. • FCC metals are more deformable • High electrical conductivity and thermal conductivity Ceramics: • Molecules are mostly characterised by both ionic and covalent bonding or in combination • Strong attractive forces within the molecules. • High hardness, electrically insulator, refractory, chemically inert • Crystalline or noncrystalline structure Polymer: • a large molecule (macromolecule) composed of repeating structural units connected by covalent chemical bonds. • Molecules together in aggregate are weakly connected by secondary bonding • Three types: thermoplastic, thermosetting plastic, elastomer

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