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1. casting class1

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  • 1. Some casting-products (casting) A simple casting technique
  • 2. Microstructure: behind the desired Properties of the product material Phases Grains various crystals structures Grain boundary unit cell atomic bonding
  • 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. 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. Metallic covalent ionic
  • 6. Dipole force Hydrogen bonding van der Waals forces
  • 7. Unit cells Crystalline structure BCC FCC Allotropic characteristics? HCP
  • 8. Imperfections in crystals Point defect ► point defect ► line defect ► surface defect
  • 9. Line defect
  • 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. 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. 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