1. Lec. 1 THE NATURE OF MATERIALS
Industrial Material Applications, IE251
Dr M. A. Eissa
King Saud University
College of Engineering
Department of Industrial Engineering

2. THE NATURE OF MATERIALS
Atomic Structure and the Elements
Bonding between Atoms and Molecules
Crystalline Structures
Noncrystalline (Amorphous) Structures

3. Importance of Materials in Manufacturing
Manufacturing is a transformation process
It is the material that is transformed
And it is the behavior of the material when subjected to the forces, temperatures, and other parameters of the process that determines the success of the operation

4. Atomic Structure and the Elements

5. Atomic Structure and the Elements
The basic structural unit of matter is the atom
Each atom is composed of a positively charged nucleus, surrounded by a sufficient number of negatively charged electrons so the charges are balanced
More than 100 elements, and they are the chemical building blocks of all matter

6. Metalloids or Semimetals
Element Groupings
The elements can be grouped into families and relationships established between and within the families by means of the Periodic Table
Metals occupy the left and center portions of the table
Nonmetals are on right
Between them is a transition zone containing metalloids or semi‑metals
Metals
Metalloids or Semimetals
NonMetals
Beryllium – Be
Boron – B
Helium – He
Lithium – Li
Silicon – Si
Neon – Ne
Magnesium – Mg
Arsenic – As
Argon – Ar
Cadmium – Cd
Antimony – Sb
Krypton – Kr
Copper- Cu
Polonium - Po
Xenon – Xe
Iron – Fe
Tellurium - Te
Radon – Rn
Zinc – Zn
Germanium - Ge
Fluorine – F
Titanium – Ti
Chlorine – Cl
Gold – Au
Oxygen – O

7. Periodic Table
Figure 2.1 Periodic Table of Elements. Atomic number and symbol are listed for the 103 elements.

8. Question? What are the noble metals? Copper Silver Gold
Noble metals (precious metals) are metals that are resistant to corrosion or oxidation, unlike most base metals.
Platinum (Pt), Palladium (Pd)

9. Bonding between Atoms and Molecules

10. Bonding between Atoms and Molecules
Atoms are held together in molecules by various types of bonds
Primary bonds - generally associated with formation of molecules
Secondary bonds - generally associated with attraction between molecules
Primary bonds are much stronger than secondary bonds

11. Bonding between Atoms and Molecules
Primary
Bonding
Secondary
Bonding
Ionic
Covalent
Metallic
Dipole forces
London forces
Hydrogen bonding

12. The ones on the outer shell
Primary Bonds
Characterized by strong atom‑to‑atom attractions that involve exchange of valence electrons
Following forms:
Ionic
Covalent
Metallic
The ones on the outer shell

13. Ionic Bonding
Atoms of one element give up their outer electron(s), which are in turn attracted to atoms of some other element to increase electron count in the outermost shell.
Properties:
Poor Ductility
Low Electrical Conductivity
Example: Sodium Chloride (NaCl)
Figure 2.4 First form of primary bonding: (a) Ionic

14. Covalent Bonding Properties: High Hardness Low Electrical Conductivity
Outer electrons are shared between two local atoms of different elements.
Properties:
High Hardness
Low Electrical Conductivity
Examples: Diamond, Graphite
Figure 2.4 Second form of primary bonding: (b) covalent

15. Metallic Bonding
Outer shell electrons are shared by all atoms to form an electron cloud.
Properties:
- Good Conductor (Heat and Electricity)
- Good Ductility
Figure 2.4 Third form of primary bonding: (c) metallic

16. Secondary Bonds
Secondary bonds involve attraction forces between molecules (whereas primary bonds involve atom‑to‑atom attractive forces),
No transfer or sharing of electrons in secondary bonding
Bonds are weaker than primary bonds
Three forms:
Dipole forces
London forces
Hydrogen bonding

17. Macroscopic Structures of Matter
Atoms and molecules are the building blocks of more macroscopic structure of matter
When materials solidify from the molten state, they tend to close ranks and pack tightly, arranging themselves into one of two structures:
Crystalline
Noncrystalline

18. Crystalline Structures

19. Crystalline Structure
Structure in which atoms are located at regular and recurring positions in three dimensions
Unit cell - basic geometric grouping of atoms that is repeated
The pattern may be replicated millions of times within a given crystal
Characteristic structure of virtually all metals, as well as many ceramics and some polymers

20. Crystallinity
When the monomers are arranged in a neat orderly manner, the polymer is crystalline. Polymers are just like socks. Sometimes they are arranged in a neat orderly manner.
An amorphous solid is a solid in which the molecules have no order or arrangement. Some people will just throw their socks in the drawer in one big tangled mess. Their sock drawers look like this:

21. What about glass?! Does glass have a crystalline structure?!
Question?
What about glass?! Does glass have a crystalline structure?!
"What is glass... is it a liquid or a solid?"
Antique windowpanes are thicker at the bottom, because glass has flowed to the bottom over time!
Glass has no crystalline structure, hence it is NOT a solid.
Glass is a supercooled liquid.
Glass is a liquid that flows very slowly.
Glass is a highly viscous liquid!!

22. Three Crystal Structures in Metals
Body-centered cubic (BCC)
Face centered cubic (FCC)
Hexagonal close-packed (HCP)
# of atoms in unit cell: 9
# of atoms: 14
# of atoms: 17
Figure 2.8 Three types of crystal structure in metals.

23. Crystal Structures for Common Metals
Room temperature crystal structures for some of the common metals:
Body‑centered cubic (BCC)
Chromium, Iron, Molybdenum, Tungsten
Face‑centered cubic (FCC)
Aluminum, Copper, Gold, Lead, Silver, Nickel, (Iron at 1670oF)
Hexagonal close‑packed (HCP)
Magnesium, Titanium, Zinc

24. Body-Centered Cubic Crystal Structure
Figure 1.2 The body-centered cubic (bcc) crystal structure: (a) hard-ball model; (b) unit cell; and (c) single crystal with many unit cells. Source: W. G. Moffatt, et al., The Structure and Properties of Materials, Vol. 1, John Wiley & Sons, 1976.

25. Face-Centered Cubic Crystal Structure
Figure 1.3 The face-centered cubic (fcc) crystal structure: (a) hard-ball model; (b) unit cell; and (c) single crystal with many unit cells. Source: W. G. Moffatt, et al., The Structure and Properties of Materials, Vol. 1, John Wiley & Sons, 1976.

26. Hexagonal Close-Packed Crystal Structure
Figure 1.4 The hexagonal close-packed (hcp) crystal structure: (a) unit cell; and (b) single crystal with many unit cells. Source: W. G. Moffatt, et al., The Structure and Properties of Materials, Vol. 1, John Wiley & Sons, 1976.

27. Imperfections (Defects) in Crystals
Imperfections often arise due to inability of solidifying material to continue replication of unit cell, e.g., grain boundaries in metals
It is in fact: Deviation in the regular pattern of the crystalline lattice structure.
Studying about imperfections is important:
Imperfection is bad: a perfect diamond (with no flaws) is more valuable than one containing imperfections.
Imperfection is good: the addition of an alloying ingredient in a metal to increase its strength (this is an imperfection which is introduced purposely).

28. Types of defects or imperfections
Point defects,
Line defects,
Surface defects.

29. Point Defects
Imperfections in crystal structure involving either a single atom or a few number of atoms
Dislocation of an atom
Extra atom present
Figure 2.9 Point defects: (a) vacancy, (b) ion‑pair vacancy (Schottky), (c) interstitialcy, (d) displaced ion (Frenkel Defect).

30. Defects in a Single-Crystal Lattice
Figure 1.9 Schematic illustration of types of defects in a single-crystal lattice: self-interstitial, vacancy, interstitial, and substitutional.

31. Line Defects
Defect happens along a line ( Connected group of point defects that forms a line in the lattice structure)
Most important line defect is a dislocation, which can take two forms:
Edge dislocation
Screw dislocation

32. Edge Dislocation
Edge of an extra plane of atoms that exists in the lattice
Figure Line defects: (a) edge dislocation

33. Movement of an Edge Dislocation
Figure Movement of an edge dislocation across the crystal lattice under a shear stress. Dislocations help explain why the actual strength of metals in much lower than that predicted by theory.

34. Screw Dislocation
Spiral within the lattice structure wrapped around an imperfection line, like a screw is wrapped around its axis
Figure Line defects: (b) screw dislocation

35. Surface Defects
Imperfections that extend in two directions to form a boundary
Examples:
External: the surface of a crystalline object is an interruption in the lattice structure
Internal: grain boundaries are internal surface interruptions

36. Elastic Strain

37. Elastic Strain
When a crystal experiences a gradually increasing stress, it first deforms elastically
If force is removed lattice structure returns to its original shape
Figure 2.11 Deformation of a crystal structure: (a) original lattice: (b) elastic deformation, with no permanent change in positions of atoms.

38. Plastic Strain
If stress is higher than forces holding atoms in their lattice positions, a permanent shape change occurs
Figure 2.11 Deformation of a crystal structure: (c) plastic deformation (slip), in which atoms in the lattice are forced to move to new "homes“.

39. Effect of Dislocations on Strain
In the series of diagrams, the movement of the dislocation allows deformation to occur under a lower stress than in a perfect lattice.
Slip involves the relative movement of atoms on the opposite sides of a plane in the lattice, called slip plane.
Figure Effect of dislocations in the lattice structure under stress.

40. Slip on a Macroscopic Scale
When a lattice structure with an edge dislocation is subjected to a shear stress, the material deforms much more readily than in a perfect structure.
Dislocations are a good‑news‑bad‑news situation
Good news in manufacturing – the metal is easier to form
Bad news in design – the metal is not as strong as the designer would like

41. Twinning
A second mechanism of plastic deformation in which atoms on one side of a plane (the twinning plane) are shifted to form a mirror image of the other side
Figure Twinning, involving the formation of an atomic mirror image on the opposite side of the twinning plane: (a) before, and (b) after twinning.

42. Polycrystalline Nature of Metals
A block of metal may contain millions of individual crystals, called grains
Such a structure is called polycrystalline
Each grain has its own unique lattice orientation; but collectively, the grains are randomly oriented in the block

43. Crystalline Structure
How do polycrystalline structures form?
As a block of metal cools from the molten state and begins to solidify, individual crystals nucleate at random positions and orientations throughout the liquid
These crystals grow and finally interfere with each other, forming at their interface a surface defect ‑ a grain boundary
Grain boundaries are transition zones, perhaps only a few atoms thick
Grain
Grain
boundary
Growth of crystals in metals

44. Noncrystalline (Amorphous) Structures

45. Noncrystalline (Amorphous) Structures
Many materials are noncrystalline
Water and air have noncrystalline structures
A metal loses its crystalline structure when melted
Some important engineering materials have noncrystalline forms in their solid state:
Glass
Many plastics
Rubber

46. Features of Noncrystalline Structures
Two features differentiate noncrystalline (amorphous) from crystalline materials:
Absence of long‑range order in molecular structure
Differences in melting and thermal expansion characteristics
What are the differences between them?

47. Crystalline versus Noncrystalline
The crystal structure is regular, repeating, and denser
The noncrystalline structure is random and less tightly packed.
Figure 2.14 Difference in structure between: (a) crystalline and (b) noncrystalline materials.

48. Solidification
Alloy Metal
Pure Metal

49. Volumetric Effects
Tg=glass temperature
Tm=melting temperature
Figure Characteristic change in volume for a pure metal (a crystalline structure), compared to the same volumetric changes in glass (a noncrystalline structure).

50. Summary: Characteristics of Metals
Crystalline structures in the solid state, almost without exception
BCC, FCC, or HCP unit cells
Atoms held together by metallic bonding
Properties: high strength and hardness, high electrical and thermal conductivity
FCC metals are generally ductile

51. Summary: Characteristics of Ceramics
Most ceramics have crystalline structures, while glass (SiO2) is amorphous
Molecules characterized by ionic or covalent bonding, or both
Properties: high hardness and stiffness, electrically insulating, refractory, and chemically inert ?
Refractory materials retain their strength at high temperatures. They are used to make crucibles and linings for furnaces, kilns and incinerators.

52. Summary: Characteristics of Polymers
Many repeating mers in molecule held together by covalent bonding
Polymers usually carbon plus one or more other elements: H, N, O, and Cl
Amorphous (glassy) structure or mixture of amorphous and crystalline
Properties: low density, high electrical resistivity, and low thermal conductivity, strength and stiffness vary widely