EAS107
Introduction to Engineering
Materials and Aeromaterials
Recommended Textbook
Study Unit 1
Chapter 3
Atomic and Ionic Arrangements
Atomic and Ionic Arrangements
Play an important role in determining the
• microstructures, and
• properties of engineering materials
Atomic and Ionic Arrangements
Techniques used for characterization of
crystalline solids
• x-ray diffraction (XRD)
• transmission electron microscopy (TEM)
• electron diffraction
Atomic and Ionic Arrangements
Types of arrangements found in different states
of matter
• No order
monoatomic gases
• Short-range order
amorphous materials
• Long-range order (>100 nm)
crystalline materials
No order, SRO & LRO
No order, SRO & LRO
Lattice & Unit Cell
Lattice Parameter
7 Crystal Systems
No. of Atoms per Unit Cell
No. of Atoms per Unit Cell
Example 3-1 on page 58
Determining the Number of Lattice
Points in Cubic Crystal Systems
Atomic Radius vs Lattice Parameter
Atomic Radius vs Lattice Parameter
Example 3-2 on page 58
Determining the Relationship between
Atomic Radius and Lattice Parameters.
Coordination Number
Crystal Structure of Metals
Study Unit 1
Chapter 4
Imperfection in the Atomic and Ionic
Arrangements
Imperfection in Arrangements
Arrangement of the atoms / ions in materials
contains imperfections / defects.
These defects have a profound effect on the
properties of materials.
Imperfection in Arrangements
3 basic types of imperfections:
• Point defects
• Line defects (dislocations)
• Surface defects
Point Defects
Point Defects
Screw Dislocations
Edge Dislocations
Mixed Dislocations
Slip by Edge Dislocations
Evidence of Dislocations
Surface Defects
Boundaries / planes that separate a material
into regions, each having the same crystal
structure but different orientations.
• Materials Surface
• Grain boundaries
• Small angle grain boundaries
• Stacking faults
• Twin boundaries
• Domain boundaries
ASTM Grain Size Number
Hall-Petch Equation
σy = σ0 + Kd -1/2
Where
σy = yield strength
σ0 = constant
K = constant
d = average grain diameter
Surface Defects
Example 4-12 on page 125
Design of a Mild Steel
Surface Defects – Grain Boundaries
Surface Defects
Example 4-13 on page 127
Calculation of ASTM Grain Size Number
Surface Defects
Importance of Defects
• Effect on mechanical properties via control
of the slip process
• Strain hardening
• Solid-solution strengthening
• Grain-size strengthening
• Effects on electrical, optical & magnetic
properties
Importance of Defects
Study Unit 1
Chapter 5
Atom and Ion Movements in Materials
Chapter 5
• Kinetics of diffusion
• Effect of concentration gradient &
temperature
• Overview of Fick’s Laws – quantitative
calculation of diffusion
Applications of Diffusion
• Case hardening of steels
• Dopant diffusion for semiconductors
• Conductive ceramics
• Plastic beverage bottles
• Oxidation of aluminium
• Coatings & thin films
• TBC for turbine blades
• Optical fibres & microelectronic parts
Applications of Diffusion
Rate of diffusion of atoms and molecules is
higher in gases and liquids than in solids.
Stability of Atoms and Ions
Arrhenius equation:
Rate of Diffusion = c0 exp (-Q/RT)
Where
c0 = constant
R = gas constant (1.987 cal / mol.K)
T = absolute temperature (K)
Q = activation energy (cal / mol)
Stability of Atoms and Ions
Stability of Atoms and Ions
Problem 5-8 on page 177
Using Arrhenius equation to
calculate the jump rate at 750oC.
Mechanisms for Diffusion
Interdiffusion
Diffusion of unlike atoms in different directions
Mechanisms for Diffusion
Mechanisms for Diffusion
• More interstitial sites, smaller interstitial atoms
• Interstitial diffusion occurs more easily than
vacancy diffusion (self-diffusion).
Activation Energy for Diffusion
Activation Energy for Diffusion
Activation Energy for Diffusion
Problem 5-15 on page 178
Calculate
(a) the activation energy
(b) the constant D0
Rate of Diffusion
Rate of Diffusion
Fick’s First Law:
J = -D (dc/dx)
Where
J = the flux
D = diffusivity or diffusion coefficient
dc/dx = concentration gradient
Rate of Diffusion
Factors Affecting Diffusion
Diffusion Coefficient:
D = D0 exp (-Q/RT)
Where
D0 = constant
R = gas constant (1.987 cal / mol.K)
T = absolute temperature (K)
Q = activation energy (Cal / mol)
Factors Affecting Diffusion
Factors Affecting Diffusion
Problem 5-25 on page 178
Determine
(a) the concentration gradient of H2
(b) the flux of H2 through the foil
Factors Affecting Diffusion
Types of Diffusion
• volume diffusion
• grain boundary diffusion
• surface diffusion
Factors Affecting Diffusion
Factors Affecting Diffusion
Time
• High temperature
• Small diffusion distances
reduce time to produce a uniform structure.
Factors Affecting Diffusion
Bonding & Crystal Structure
• Strength of atomic bonding
• Size of ions ( cations is smaller )
Factors Affecting Diffusion
Permeability of Polymers
Permeability is used instead of diffusion coefficients.
Concern with penetration of atoms or small molecules
(air or water) through the long polymer chains.
Express in term of volume of gas or vapour that can
permeate per unit area / time / thickness at specific
temperature and relative humidity.
Permeability of Polymers
In general, the more compact the polymer structure,
the lesser the permeability.
Crystalline polymer has lower permeability than the
amorphous polymer, and
high-
high-density polymer has lower permeability than the
low-
low-density polymer.
Permeability of Polymers
• Air diffusion through plastic packaging film may
spoil the food.
• Oil absorption into polymer o-
o-ring may cause
swelling.
• Selective diffusion through polymer membrane is
used for water desalination.
• Diffusion is desirable to uniformly dye the synthetic
polymer fabric.
Composition Profile
Fick’s Second Law:
Describes the dynamic, non-steady state,
diffusion of atoms using a differential
equation.
Composition Profile
Composition Profile
Problem 5-35 on page 179
Compare the diffusion rate, and explain the
difference.
Diffusion & Materials Processing
• Melting and Casting
• Sintering
• Grain growth
• Diffusion bonding
Diffusion & Materials Processing
Diffusion & Materials Processing
Diffusion & Materials Processing
Problem 5-60 on page 180
What is the activation energy for the
diffusion bonding process?
