Materials Science and Engineering
by Kadri Aydınol (D-103)
any version of the book (W.D. Callister, Materials Science and Engineering an Introduction)
down to the 4th edition will do.
Chapter 1: Introduction
Engineering properties are very much dependent on the structure of matter, although METE is
not directly concerned with the structure
a basic classification system for materials:
● metals and alloys: metallic elements or combinations. Large number of nonlocalized
electrons so good heat-electricity conductors, opaque, strong but deformable
● ceramics: metal-nonmetal compounds, heat and electricity insulators, resistant to high
temperature and harsh environments, hard but brittle
● polymers: C, H and other nonmetallic based organic compounds. Large molecular
structure, low density, extremely flexible
● composites: consists more than one type, displays a combination of best characteristics
● semiconductors: electrical properties intermediate between conductors and insulators
● biomaterials: implanted in human body, must be nontoxic and compatible with body
Properties depend on structure: ex: hardness vs structure of steel. Examining the
microstructures of steel with different cooling rates, we observe different clusters in the
structure: higher cooling rate (“quenching”) yields greater hardness. So here we have the
processing changing the structure. Electrical resistivity of copper, for example, can be
increased by adding impurities or deforming.
The Materials Selection Process
1. Pick Application, determine required Properties (mechanical, electrical, thermal,
magnetic, optical, deteriorative)
2. From the Properties, identify candidate Material(s) with their structure and
3. Identify the required Processing to change structure and overall shape (casting,
sintering, vapor deposition, doping, forming, joining, annealing)
Thermal properties: thermal expansion, thermal conductivity and thermal shock resistance
Thick glass cup with hot liquid poured into it will actually fracture more easily since the
difference between the inner and outer surfaces is larger Magnetic properties: variety of applications: electric motors, medical imaging, data storage
etc. Strength also depends on composition, adding 3 atomic % Si makes Fe a better recording
Optical properties: transmittance of aluminum oxide depends on material structure: higher
porosity yields lower transparency
Deteriorative properties: stress and saltwater causes cracks in metals, heat treatment slows
crack speed in salt water
Chapter 2: Bonding and Properties
Issues to address: What promotes bonding, what types of bonds are there? What properties
are inferred from bonding?
Bohr atom model (discrete orbitals) vs Wave Mechanical Model (probabilistic orbitals)
Electrons in the wave mechanical model tend towards empty orbitals with lowest energy
n: 1, 2, 3, 4 - principal quantum number
l: s, p, d, f - second quantum number
m İ 1, 3, 5, 7 - number of energy states
m s magnetic spin
2 2 6 2 2
Si (Z = 14) has the configuration 1s 2s 2p 3s 3p
Stable electron configurations: noble gases have complete s and p subshells and tend to be
unreactive. Most elements have unstable configurations.
In the periodic table, elements in a column have similar valance structure. On the left we have
the electropositive elements that readily give up electrons to become + ions, and vice versa.
Energy State Diagrams may contain stable (global minimum), unstable and metastable (local
minimum) states. The amount of activation energy needed to carry the system from one state to
another determines the rate of reaction / direction of movement between states
Atomic Bonding: atoms form bonds to lower their energy. for each pair of atoms we have a
certain distance called the equilibrium interatomic spacing, at which the attractive and repulsive
forces between the atoms balance each other. To be able to break the bond (ie pull the atoms
infinitely far away) at least 0 amount of energy will be needed (bond energy). Ionic Bonding: occurs between + and - ions with large differences in electronegativity, requires
electron transfer. Predominant bonding in ceramics. Between the ions themselves, there will
be coloumbic attraction. As a result, we will have the ions with stable electron configuration.
The specific arrangement of ions (alternating sequence of anions and cations) keeps the
structure from collapsing and imploding. This structure also brings about the brittleness of
Covalent Bonding: Requires shared electrons. Electronegativities are comparable. Possible
between nonmetals, as well as metals and nonmetals. A few ceramic materials (carbides and
borides) form covalent bonds. Bond strength can vary (from bismuth to diamond).
Metallic Bonding: Generally strong bonds arising from a sea of donated valance electrons.
Primary bond for metals and their alloys.
Secondary bonding: weak bonds arising from interaction between dipoles (fluctuating
dipoles with asymmetric electron clouds or molecule-induced permanent dipoles), such as Van
der Waals forces. Can occur in liquids or polymers, the weak bonds are why they have low
Properties from bonding - Melting Temperature
● stretching the bonds beyond the bonding distance decreases the bonding energy
● lower bonding energy gives lower melting temperature
● liquids and solids are distinguised according to fluidity/viscosity, concerning the
movement of atoms/molecules.
● large for ceramics, moderate for metals, low for polymers
● for polymers we have another defined temperature called “glass transition temperature”
where the material is neither liquid nor solid
Properties from bonding - Elasticity
● elasticity is about the material resuming its original shape when force is removed
● lower elastic modulus means material is easier to deform
● elastic modulus is larger if the bond energy is larger or if the curvature of the energy
curve at the bond length is less steep - to achieve the same amount of seperation
between atoms, we have to provide more energy for a material with less steep energy
curve. (E ~ curvature at0r )
● large elastic modulus for ceramics, moderate for metals, small for polymers
Properties from bonding - Thermal Expansion
● the thermal expansion coefficient alpha is larger0if E is smaller.
● alpha ~ symmetry at r0 ● small for ceramics, moderate for metals, large for polymers
Chapter 3: Crystal Structures and Properties
How do atoms assemble into solid structures? How does density depend on structure? When to
material properties vary with sample/part orientation?
Energy and Packing: dense, regularly packed structures tend to have lower energy. summing
the energies of all pairs in a non-dense random packing would yield a large energy value for the
system, which would be unstable.
Materials and Packing:
● in crystalline materials, we have periodically packed atoms in 3D arrays, which is
typical of metals, many ceramics and some polymers
● in noncrystalline (amorphous) materials we have no period packing, typical of complex
structures and rapid cooling
To identify the crystal structure, look for repeating patterns (in terms of repeating surrounding
atoms) by placing imaginary lattice points, then connecting these lattice points to create a 3D
structure. There are six parameters (3 edge lengths, 3 planes) defining this shape. Depending
on these parameters we have 7 different crystal systems.
● cubic - 3 edges same, angles orthogonal
● tetragonal - 2 edges same, angles orthogonal
● orthorombic - arbitrary edges, angles orthogonal
● triclinic - all arbitrary edges with arbitrary angles
we don’t have, for example, pyramids as a crystal systems, because it lacks the property of
filling space as we repeat it over the axes.
● tend to be densely packed, with simple crystal structures
● reason for dense packing: typically has only one element so all atomic radii is the same,
nearest neighbor distances tend to be small, metal bonding isn’t directional
Atomic Packing Factor (APF) Simple Cubic Structure (SC) - rare due to poor packing, close packed directions are cube
edges. coordination number = 6 (# nearest neighbors), APF of 0.52
Body Centered Cubic Structure (BCC)- close packed directions are cube diagonals,
coordination number=8, APF of 0.68
Face Centered Cubic Structure (FCC) - close packed directions are face diagonals,
coordination number=12, APF of 0.74, best possible packing for equal-sized atoms, considered
to be a “closely packed” structure
Hexagonal Close-packed Structure (HCP) - coordination number=12, APF of 0.74
Theoretical Density, ro
differs slightly from the actual value
Metals have larger theoretical density due to their close packing (metallic bonding) and large
Crystals as Building Blocks
As the size of the structure grows, keeping all blocks in the same orientation becomes more
During the transformation from liquid to solid, first a few atoms come together to form a nucleus
or seed, then more and more atoms will join it to cause solidification. If several seeds form, they
will almost certainly be at different orientations and thus will grow blocks (grains) with different
orientation (polycrystal). Most engineering materials are polycrystals.
In very few cases it is possible to grow the structure from a single seed with a homogenous
arrangement (single-crystal). Both are advantageous in different scenarios.
Directions in the form of [uvw]: find the projections along the three axes in fractions of the unit
distances on each axis & reduce them to smallest integers
Planes in the form of (hkl): find the intercepts on the three axes in fractions of the unit distances
on each axis, take the reciprocals and reduce them to smallest integers. For planes parallel to
one of the axes, one of the intercepts can be infinity, giving the number zero with its reciprocal.
Single vs Polycrystals
Sİngle Crystals: Properties vary with direction (anisotropic), for example in BCC iron the
elastic modulus varies with crystal direction (crystal direction dependent). Polycrystals: Properties may or may not vary with direction. If grains are randomly oriented,
properties are isotropic (since all grains are randomly oriented, the overa