Introduction to Engineering Metallurgy.pptx

Introduction to Engineering Metallurgy

1. Engineering Metallurgy Lecture I Materials Science & Engineering. Materials Performance. Classification of Materials.

2. Materials Science and Engineering Material science: the relation between the structures and properties of materials. Material Engineering: the use of the material to produce a predetermined set of properties. Selecting the best material is usually a difficult task Tradeoffs between different material properties, including cost.

3. Properties: mechanical, physical, electrical, thermal, magnetic, optical, deteriorative, production and aesthetic. Processing Structure Properties Performance

4. Choose a material for a cup to hold a liquid

5. Performance Life and deterioration Cost Appearance Durability

6. Material selection High modulus. High yield strength Hard Tough

7. Material selection High modulus. Strong Hard Tough

8. Atomic Structure Atoms: nucleus, protons, neutrons, electrons. Electron configuration and the quantum numbers. Atomic number. Atomic mass and Atomic mass unit. Valence electrons.

9. Periodic Table

10. Of the 106 elements: 82 metals. 18 nonmetals. 6 metalloids.

11. Bonding Force and Energy The net force between the two atoms: Fn=Fa+Fr At equilibrium: Fa+Fr=0 The bonding energy for these two atoms, E , corresponds to the energy at the minimum point; it represents the energy that would be required to separate these two atoms to an infinite separation.

12. Types of Bonding Primary Bonds Ionic bonding. Covalent bonding. Metallic bonding. Secondary Bonds Van der Walls (London, Dipole-Dipole) Bonding. Hydrogen bonding.

13. Ionic Bonds In compounds that are composed of both metallic and non metallic. The attractive bonding forces are coulombic. Nondirectional: the magnitude of the bond is equal in all directions around an ion. Bonding energy (600-1500 kJ/mol) are relatively large….High melting temperatures. Ceramics.

14. Covalent Bonding Stable electron configurations are assumed by the sharing of electrons between adjacent atoms. Directional: between specific atoms and may only exist only in direction between one atom and another that participate in the electron sharing. Silicate ceramics, glasses, diamond, polymers, water. It is possible to have interatomic bonds that are partially ionic and partially covalent, and in fact, very few compounds exhibit pure ionic or covalent bonding: the higher the difference in electronegativity , the more ionic the bond, and vice versa.

15. Metallic Bonding Valence electrons are not bound to any particular atom in the solid and are more or less free to drift throughout the entire metal forming a sea of electrons or an electron cloud. Energies range from 68 kJ/mol for mercury to 850 kJ/mol for Tungesten. For all elemental metals and their alloys.

16. Van der Waals Bonding From atomic or molecular dipoles. Coloumbic attraction between the positive end of one dipole and the negative end of another. 10 kJ/mol.

17. Hydrogen Bonding The hydrogen, less electronegative than the oxygen acquire a positive charge. An attraction between the positively charged hydrogen and the negatively charged oxygen of another molecule. Keeps water liquid at room temperature.

18. Bonding energies and melting temperatures for various substances Bonding type Substance Bonding energy (kJ/mol) Melting temperature ( C) Ionic NaCl 640 801 MgO 1000 2800 Covalent Si 450 1410 C (diamond) 713 >3550 Metallic Hg 68 -39 Al 324 660 Fe 406 1538 W 849 3410 Van der Waals Ar 7.7 -189 Cl 2 31 -101 Hydrogen NH 3 35 -78 H 2 O 51

19. Classification of Materials

20. Metals Solid at normal temperature (except Mercury). Large number of nonlocalized electrons. Good conductors of electricity and heat. Non transparent to visible light. Most metals are magnetic. Strong, yet deformable.

21. Iron and steels Aluminium and its alloys Copper and its alloys Nickel and its alloys Titanium and its alloys

22. Ceramics Compounds between metallic and nonmetallic elements. Most frequently: oxides, nitrides and carbides. Insulative and poor heat conductors. More resistant to high temperatures and hursh environments than metals and polymers. Hard, but brittle.

23. Alumina (Al 2 O 3 , emery, sapphire) Magnesia (MgO) Silicon carbide (SiC) Silicon nitride (Si 3 N 4 ) Cement and concrete

24. Polymers Plastic and rubber materials. Many of them are organic compounds that are based on carbon, hydrogen … Very large molecular structure. Low density and may be extremely flexible.

25. Polyethylene (PE) Polymethylmethacrylate (PMMA) Polyamide (PA) Polystyrene (PS) Polyurethane (PU) Polyvinylchloride (PVC) Polyethylene tetraphthalate (PET) Polyethylether Ketone (PEEK) Epoxies (EP) Elastomers, such as natural rubber (NR)

26. Glasses What is a glass material: super-cooled liquid. (highly viscous) All of the above materials can be produced in a glassy form (non crystalline) using fast cooling.

27. Composites An engineered material to display a combination of the best characteristics of each of the component materials. Glass Fibre Reinforced Polymer (GFRP): Strength: glass fibre flexibility: polymer matrix

28. New types of materials Semiconductors & Superconductors: it has revolutionized our life. Biomaterials: must be compatible with body tissues and not to produce toxic substances. Advanced Materials: materials for HiTec applications. Smart Materials: sensor – processor – actuator: piezoelectric ceramics, magnetoresistive materials. Nanomaterials: design new materials built from simple atomic level constituents – carbon nanotubes.

29. Crystalline vs. Amorphous A crystalline material is the one in which the atoms are situated in a repeating or periodic array over large atomic distances (long range order). Amorphous solids lack a systematic and regular arrangement of atoms over relatively large atomic distances (non-crystalline, super-cooled liquid).

30. Rapid cooling through the freezing temperature favours the formation of a noncrystalline solid.

31. Anistropy : directionality of properties. Substances in which measured properties are independent of the direction of measurement are termed isotropic.