1. Introduction
I.Materials Science and Engineering
• Materials Science Involves investigating the relationships that exist between the structures and properties of materials.
• Material Engineering is designing or engineering the structure of a material to produce a predetermined set of properties.
• Structure is the arrangement of its internal components. There are 4 levels:
1.Atomic Structure ( < 10-9m)
2.Crystal Structure ( > 10-9m, < 10-7m) 3.Microscopic Structure (>10-7m,<10-3m) 4.Macroscopic Structure (>10-3m)
2. Classification of Materials
• Solid materials have been grouped into three basic classifications: metals,
ceramics, and polymers.
• Metals
• Metallic materials are normally
combinations of metallic elements (Fe, Cu, Al, etc.). They have large numbers of non- localized electrons.
• Ferrous Metals.
• Non-Ferrous Metals.
• Ceramics
• Ceramics are compounds between
metallic and nonmetallic elements. They are most frequently oxides, nitrides, and carbides (SiO2, Al2O3, Si3N4, BN, SiC, WC, etc.).
• Traditional Ceramics. (Cement, Tile, Whiteware, etc.)
Advanced Ceramics
• Structural Ceramics : Engine parts, Abrasive, High temperature strength, etc..
• Electronic Ceramics : Semiconductor, superconductor, Insulator, Fiber optic, etc..
Polymers
• Polymers are normally organic compounds that are chemically based on carbon,
hydrogen, and other nonmetallic elements and they have very large molecular
structure consisting of many mers.
• Thermoplastic Polymers : Molecular structure is linear or flexible chains. Soften when heated. Ex. Plastic.
• Thermosetting Polymers : Molecular
structure is cross-linked or network. Hard and brittle. Ex. Epoxy.
• Elastomer Polymers: Molecular structure is intermediate between thermoplastic and thermosetting. Ex. rubber.
Composites
• Composite materials are the materials that consist of more than one material type. A composite is designed to display a
combination of the best characteristics of each of the component material
Atomic Bonding in Solids
I. Bonding Forces and Energies FN = FA+ FR
FN : Net force between two atoms.
FA : Attractive force due to bonding.
FR : Repulsive force due to overlap of outer electron shells.
Two atoms are in equilibrium when FN= 0 The potential energy, E= F∫ dr
∞ r
5.1 (a) The dependence of repulsive, attractive, and net forces on interatomic separation for two isolated atoms.
(b) The dependence of repulsive, attractive, and net potential energies on interatomic separation for two isolated atoms.
II. Primary Interatomic Bonds
(Ionic Bonding, Covalent Bonding, and Metallic Bonding.)
Ionic Bonding
• In compounds that are composed of both metallic and non-metallic elements, Atoms of a metallic element give up their valence electrons to the non-metallic atoms.
• The attractive bonding forces are coulombic; that is, the positive and negative ions attract one another.
• Most ceramic materials are ionic bonding.
• Bonding energies and melting temperatures are high.
Covalent bonding
• Adjacent atoms are sharing the electrons to create stable electron configuration.
• Polymer and some ceramic materials are covalent bonding.
• Bonding energies may be high or low.
Metallic Bonding
• The valence electrons of metallic materials (1, 2, or 3 electrons per atom) are free to drift throughout the entire metal.
• These electrons act as a glue to hold the ion cores (the atom without valence electrons) together.
• Bonding energies may be weak or strong.
3. Crystal Structure
I . Fundamental concepts
• A crystalline material is one in which the atoms are situated in a repeating array over large atomic distance in three-dimensional pattern.
• All metals, many ceramics, and certain polymers forms crystalline structure under normal solidification condition.
• Atomic hard sphere model: The atoms (or ions) are thought of as being solid spheres having well-define diameters and touching the nearest- neighbor spheres (atoms).
• Unit cellis the basic structural unit of the repetitive pattern of the crystal structures.
II. Crystal Structures
• There are 7 crystal systems (depending on the shape of the unit cell) and 14 types of crystal structures.
• Three relatively simple crystal structures are found for most of the common metals : face- centered cubic, body-centered cubic, and hexagonal close-packed.
• Coordination numberis the number of the nearest-neighbor or touching atoms.
• Atomic packing factor (APF) is the fraction of
Face-centered cubic crystal structure
Face-centered cubic (FCC) : Coordination number = 12
APF = 0.74 (close-packed)
a
R 2 2
a =
Body-centered cubic crystal structure
Body-center cubic (BCC) Coordination number = 8 APF = 0.68
3 4R a =
Hexagonal close-packed crystal structure
Hexagonal close-packed (HCP) Coordination number = 12
APF = 0.74 (close-packed) a = 2R
c = 1.633 a
III. Crystalline and noncrystalline materials Single Crystals: The repeated arrangement of
atoms is perfect throughout the entire specimen without interruption.
Ex. electronic microcircuits and some semiconductors.
Polycrystalline Materials :
• Most crystalline solids are composed of a collection of many small crystals or grains.
During solidification, small crystals or nuclei form at various positions and growth in
random crystallographic orientations.
Grain boundary is the region where two grains meet.
Noncrystalline solids (amorphous) : solids lack a systematic and regular arrangement of atoms over relatively large atomic
distance. Ex. SiO2 (glass).
