Unit1_Material science.pptx

Science and Engineering of Materials
Dr. G. Praveen Kumar.
Assistant Professor
Mechanical Engineering Department
IIITDM Kurnool
25/07/22 Dr. G. Praveen Kumar, IIITDM Kurnool 1

Course Contents
Crystal structure, defects, crystallographic planes, directions, slip, deformation mechanical behavior,
and strengthening mechanisms.
Electrical, electronic, magnetic properties of materials, property management and case studies
alloys, steel, and aluminum alloys.
Polymeric structures, polymerization, structure-property relationships, processing property
relationships.
Natural and manmade composites, processing, properties, applications. Ceramics, manufacturing
and properties, applications.
Environmental degradation of engineering materials.
Introduction to Nano, Bio, Smart and Functional materials.

Reference Books
Text Books:
1. 1. Callister's Materials Science and Engineering, 2nd ED, Adapted by R
Balasubramaniam, 2010, ISBN-13: 978-8126521432, Wiley India Ltd.
2. 2. V Raghavan, “Materials Science and Engineering: A First Course, 5th Ed,
2004, PHI India
References & Web Resources:
1. Donald R. Askeland K Balani, “The Science and Engineering of Materials,” 2012,
Cengage Learning
2. Callister, W. D. (2000). Fundamentals of materials science and engineering (Vol.
471660817) London: Wiley.

Course Objectives
CO1 Identify and understanding of crystal structure
CO2 Describe different materials physical and chemical properties
CO3 Application of different materials for engineering structures
CO4 Estimate the development of natural and manmade materials,
evolution based on application
CO5 Analyze the requirement of present industry, scope of application
and provide novel solutions to existing problems

Course Evaluation
Description Weightage of Marks
Minor – 1 15%
Minor – 2 15%
Seminar/Case Study/Assignments 10%
Class Test/Attendance/etc. 10%
End Semester Exam 50%
Total 100%

Introduction – Design Philosophy
What is Materials science and engineering?
Materials science: Studies the relationships that exist between the structures
and properties of materials.
Materials engineering: Designing or engineering a material with a predetermined set
of properties on the basis of the structure property correlations.
Why should we know about materials? Because it is the job of the engineer to select
materials for given application based of materials structure, properties, processing,
performance and cost.

Materials in day to day life

Introduction –
Historic Perspective
• Stone → Bronze → Iron → Advanced Materials
Beginning of the Material Science - People
began to make tools from stone – Start of
the Stone Age about two million years ago.
Natural materials: stone, wood, clay, skins,
etc.

Introduction –
• The Stone Age ended about 5000 years ago with
introduction of Bronze in the Far East. Bronze is an alloy
(a metal made up of more than one element), copper + <
25% of tin + other elements.
• Bronze: can be hammered or cast into a variety of shapes,
can be made harder by alloying, corrode only slowly
after a surface oxide film forms.

Introduction –
• The Iron Age began about 3000 years ago and continues today.
Use of iron and steel, a stronger and cheaper material changed
drastically daily life of a common person.
• Age of Advanced materials: throughout the Iron Age many
new types of materials have been introduced (ceramic,
semiconductors, polymers, composites…).

Introduction –
• Understanding of the relationship among structure, properties,
processing, and performance of materials. Intelligent design of
new materials evolved.
• A better understanding of structure-composition properties
relations has lead to a remarkable progress in properties of
materials. Example is the dramatic progress in the strength to
density ratio of materials, that resulted in a wide variety of new
products, from dental materials to tennis racquets.

Introduction –
MATERIAL SCIENCE AND ENGINEERING
• Material science is the investigation of the relationship
among processing, structure, properties, and performance
of materials.
• Materials engineering is on the basis of these structure–property
correlations, designing or engineering the structure of a material
to produce a predetermined set of properties.

Introduction –

Introduction –
Structure
• the structure of a material usually relates to
the arrangement of its internal components
• Subatomic level- Electronic structure of
individual atoms that defines interaction
among atoms (interatomic bonding) and
with their nuclei.

Introduction –
• Atomic level-Arrangement of atoms or
molecules in materials relative to one
another. (for the same atoms can have
different properties, e.g. two forms of
carbon: graphite and diamond).

Introduction –
• Microscopic structure-Arrangement of
small grains of material that can be
identified by microscopy. And it is a larger
structure, which contains large groups of
atoms that are normally agglomerated
together.

Introduction –
• Macroscopic structure- Structural
elements that may be viewed with the naked
eye.

Introduction –
The structure can be divided into 4 levels :
• Structure of Atomic including of Nucleus (Proton + Neutrons)
Surrounded by electronic orbitals.
• Structure of Crystal isArray characterization of atoms or molecules.
Crystalline structures are
arranged in a metallike
order
Amorphous structures are Atoms
arranged in disorder like polymers

Introduction –
• A property is a material trait in terms of the
kind and magnitude of response to a
specific imposed stimulus. Generally,
definitions of properties are made
independent of material shape and size.
• Virtually all important properties of solid
materials may be grouped into six different
categories: mechanical, electrical, thermal,
magnetic, optical, and deteriorative.

Introduction –
• Mechanical properties relate deformation to
an applied load or force; examples include
elastic modulus and strength.
• Electrical properties, such as electrical
conductivity and dielectric constant, the
stimulus is an electric field.
• Thermal behaviorof solids can be
represented in terms of heat capacity and
thermal conductivity.

• Magnetic properties demonstrate the
response of a material to the application of
a magnetic field.
• Optical properties, the stimulus is
electromagnetic or light radiation; index of
refraction and reflectivity are representative
optical properties.
• Deteriorative characteristics relate to the
chemical reactivity of materials

Processing and
Performance.
• With regard to the relationships of these
four components, the structure of a material
will depend on how it is processed.
Furthermore, a material’s performance will
be a function of its properties.

Introduction –
Classification of Materials
• Three basic groups of solid engineering materials based on atomic bonds and
structures:
• Metals
• Ceramics
• Polymers
• Classification can also be done based on either properties (mechanical, electrical,
optical), areas of applications (structures, machines, devices). Further we can
subdivide these groups.
• According to the present engineering needs: Composites, Semiconductors,
Biomaterials

Introduction –
Metals
• Characteristics are owed to non-localized electrons (metallic bond between atoms)
i.e. electrons are not bound to a particular atom.
• They are characterized by their high thermal and electrical conductivities.
• They are opaque, can be polished to high lustre. The opacity and reflectivity of a
metal arise from the response of the unbound electrons to electromagnetic
vibrations at light frequencies.
• Relatively heavier, strong, yet deformable.
E.g.: Steel,Aluminium, Brass, Bronze, Lead, Titanium, etc.

Introduction –
Polymers
• Commercially called plastics; noted for their low density, flexibility and use as
insulators.
• Mostly are of organic compounds i.e. based on carbon, oxygen and other non-
metallic elements.
• Consists large molecular structures bonded by covalent and van der Waals
forces.
• They decompose at relatively moderate temperatures (100-400C).
• Application: packaging, textiles, biomedical devices, optical devices,
household items, toys, etc. E.g.: Nylon, Teflon, Rubber, Polyester, etc.

Introduction –
Composites
• Consist more than one kind of material; tailor made to benefit from combination of
best characteristics of each constituent.
• Available over a very wide range: natural (wood) to synthetic (fiberglass).
• Many are composed of two phases; one is matrix – which is continuous and surrounds
the other, dispersed phase.
• Classified into many groups: (1) depending on orientation of phases; such as particle
reinforced, fiber reinforced, etc. (2) depending on matrix; metal matrix, polymer
matrix, ceramic matrix.
E.g.: Cement concrete, Fiberglass, special purpose refractory bricks, plywood,
etc.

Introduction –
Semiconductors
• Their electrical properties are intermediate when compared with
electrical conductors and electrical insulators.
• These electrical characteristics are extremely sensitive to the presence
of minute amounts of foreign atoms.
• Found many applications in electronic devices over decades through
integrated circuits. In can be said that semiconductors revolutionized
the electronic industry for last few decades.

Introduction –
Biomaterials
• Those used for replacement of damaged or diseased body parts.
• Primary requirements: must be biocompatible with body tissues, must not
produce toxic substances.
• Important materials factors: ability to support the forces, low friction and
wear, density, reproducibility and cost.
• All the above materials can be used depending on the application.
• Aclassic example: hip joint.
E.g.: Stainless steel, Co-28Cr-6Mo, Ti-6Al-4V
, ultra high molecular
weight polyethelene, high purity denseAl-oxide, etc.

Introduction –
• Can be defined as materials used in high-tech devices i.e. which operates based on
relatively intricate and sophisticated principles (e.g. computers, air/space-crafts,
electronic gadgets, etc.).
• These are either traditional materials with enhanced properties or newly developed
materials with high performance capabilities. Thus, these are relatively expensive.
• Typical applications: integrated circuits, lasers, LCDs, fiber optics, thermal
protection for space shuttle, etc.
E.g.: Metallic foams, inter-metallic compounds, multicomponent alloys,
magnetic alloys, special ceramics and high temperature materials, etc.
Advanced materials

Introduction –
Future materials
• Group of new and state-of-the-art materials now being developed, and expected
to have significant influence on present-day technologies, especially in the
fields of medicine, manufacturing and defense.
• Smart/Intelligent material system consists some type of sensor (detects an
input) and an actuator (performs responsive and adaptive function).
• Actuators may be called upon to change shape, position, natural frequency,
mechanical characteristics in response to changes in temperature,
electric/magnetic fields, moisture, pH, etc.

Introduction –
Future materials (contd…)
• Four types of materials used as actuators:
- Shape memory alloys
- Piezoelectric ceramics
- Magnetostrictive materials
- Electro-/Magneto-rheological fluids
• Materials / Devices used as sensors:
- Optical fibers
- Piezoelectric materials
- Micro-electro-mechanical systems (MEMS)
- etc.

Introduction –
Typical applications
• By incorporating sensors, actuators and chip processors into system,
researchers are able to stimulate biological human like behavior.
• Fibres for bridges, buildings, and wood utility poles.
• They also help in fast moving and accurate robot parts, high speed
helicopter rotor blades.
• Actuators that control chatter in precision machine tools.
• Small microelectronic circuits in machines ranging from computers to
photolithography prints.
• Health monitoring detecting the success or failure of a product.

Why study crystal structures?
When we look around much of what we see is non-crystalline (organic things like
wood, paper, sand; concrete walls, etc. → some of the things may have some crystalline parts!).
But, many of the common ‘inorganic’materials are ‘usually ’*crystalline:
□ Metals: Cu, Zn, Fe, Cu-Zn alloys
□ Semiconductors: Si, Ge, GaAs
□ Ceramics: Alumina (Al2O3), Zirconia (Zr2O3), SiC, SrTiO3
Also, the usual form of crystalline materials (say a Cu wire or a piece of alumina)
is polycrystalline and special care has to be taken to produce single crystals
Polymeric materials are usually not ‘fully’crystalline
The crystal structure directly influences the properties of the material
Crystal structure is a description of the ordered arrangement of atoms, ions or molecules
in a crystalline material.
Gives the ‘first view’towards understanding of the properties of the crystal
Why study crystallography?
* Many of the materials which are usually crystalline can also be obtained in an amorphous form

How to define a Crystal?
Crystal
A 3D translationally periodic arrangement of atoms in a space is called a crystal.
Lattice
A 3D translationally periodic arrangement of points in a space is called a crystal.
Unit Cell

Crystal = Lattice + Motif
Motif or Basis:
typically an atom or a group of atoms associated with each lattice point
What is the relation
between the two ?
Lattice
Basis
The underlying periodicity of the crystal
Entity associated with each lattice points
Lattice how to repeat
Motif what to repeat
Crystal
Translationally periodic
arrangement of motifs
Lattice
Translationally periodic
arrangement of points

CrystalStructure 14
Crystal Structure
• Crystal structure can be obtained by attaching
atoms, groups of atoms or molecules which are
cal ed basis (motif) to the lattice sides of the
lattice point.
Crystal = Crystal Lattice + Basis
Structure

M.C. Esher : Art
with Science
Every periodic pattern (and hence a Crystal) has a unique lattice associate with it.

Crystal Structure 18
Crystal Lattice
Bravais Lattice (BL) Non-Bravais Lattice (non-BL)
 All atoms are of the same kind
 All lattice points are equivalent
 Atoms can be of different kind
 Some lattice points are not
equivalent
A combination of two or more BL

Unit Cell in 2D
• The smallest component of the crystal (group
of atoms, ions or molecules), which when
stacked together with pure translational
repetition reproduces the wholecrystal.
S
a
b
S
S
S S
S S
S S S S
S S S S
CrystalStructure

Unit Cell in 2D
• The smal est component of the crystal (group of
atoms, ions or molecules), which when stacked
together with pure translational repetition
reproduces the whole crystal.
S
S
The choice of
unit cell
is not unique.
a
b S
S
CrystalStructure

2D Unit Cell example -(NaCl)
We define lattice points ; these are points with identical
environments
CrystalStructure

Unit Cel in 3D
CrystalStructure

Three common Unit Cel in3D
CrystalStructure

• The unit cell and, consequently, the
entire lattice, is uniquely determined
by the six lattice constants: a, b, c, α,
β and γ.
• Only 1/8 of each lattice point in a
unit cell can actually be assigned to
that cell.
• Each unit cell in the figure can be
associated with 8 x 1/8 = 1 lattice
point.
Unit Cell
CrystalStructure

CrystalStructure
TYPICAL CRYSTAL STRUCTURES
3 D – 1 4 BRAVAIS LATTICES A N D THE
S E VE N CRY STAL SYSTEM
• There are only seven different shapes of
unit cell which can be stacked together to
completely fill all space (in 3 dimensions)
without overlapping.
• This gives the seven crystal systems, in
which all crystal structures can be
classified.

• CubicCrystal System(SC,BCC,FCC)
• HexagonalCrystal System(S)
• Triclinic CrystalSystem(S)
• Monoclinic CrystalSystem(S,Base-C)
• Orthorhombic CrystalSystem(S,Base-C,BC,
FC)
• TetragonalCrystalSystem(S,BC)
• Trigonal (Rhombohedral) Crystal System (S)

Coordinatıon Number
• CoordinatıonNumber (CN): TheBravaislattice points closestto agiven
point arethe nearestneighbours.
• BecausetheBravaislattice isperiodic, all pointshave the same
number of nearest neighbours or
coordination number.Itis aproperty of the lattice.
 A simple cubic has coordination number 6;
A body-centered cubic lattice, 8;
A face-centered cubic lattice,12.
CrystalStructure 36

Atomic Packing Factor
• Atomic Packing Factor (APF) is defined as the
volume of atoms within the unit cell divided by
the volume of the unitcell.

1-CUBIC CRYSTAL SYSTEM



a- Simple Cubic (SC)
Simple Cubic has one lattice point so its primitive cell.
In the unit cell on the left, the atoms at the corners are cut
because only a portion (in this case 1/8) belongs to that cell.
The rest of the atom belongs to neighboring cells.
Coordinatination number of simple cubic is 6.
a
CrystalStructure 38
b
c

Atomic Radiusfor SC
• It is half the distance between
any two nearest neighbors inthe
given crystal structure.
• It is expressedin terms ofcube
edge a
a =2r
,
r =a/2
Atomic Radius, r =0.5a
a

CrystalStructure 40
Atomic Packing Factor of SC

• APF=0.52
• That means that the percentage ofpacking is
52%
• Thus,52%of the volume of the simple cubic
unit cell is occupied by atoms and the
remaining 48%volume of unit cell is vacantor
void space.

b-Body Centered Cubic (BCC)
a
CrystalStructure
b c
BCC structure has 8 corner atoms
and 1 body centre atom.
Each corner atom is shared by 8
unit cells.
The center atom is not shared by
any of the unit cells.
So the
Number of atoms per unit cell
n = (1/8)x8 +1 = 2

b-Body Centered Cubic (BCC)
 BCC has two lattice points so BCC
is a non-primitive cell.
 BCC has eight nearest neighbors.
Each atom is in contact with its
neighbors only along the body-
diagonal directions.
Hence, the coordination no.

for BCC unit cell is 8
 metals (Fe,Li,Na..etc),
Many
including
transition
the alkalis and several
elements choose the
BCC structure.
a
CrystalStructure
b c

Atomic Radius for BCC unit cell
r =a x (3)1/2/4

CrystalStructure 45
2 (0,433a)
Atomic Packing Factor of BCC

The percentage of packing for BCC structure is 68%
Thus , 68% of the volume of body centered cubic cell
is occupied by atoms and the remaining 32% of the
volume is vacant or void space

c- Face Centered Cubic (FCC)
FCC structure has 8 corner
atoms and 6 face centre atoms.
Each corner atom is shared by 8
unit cells.
Each face centered atom is
shared by 2 unit cells.
So the
Number of atoms present in unit
cell is
n = (1/8 x8) + (1/2 x 6)
= 1 + 3
= 4

48
• Co ordination Number
• The corner atom in its own plane touches 4 face centred
atoms.
• In the plane just above, the corner atom has another 4
face centered atoms as its nearest neighbours
• Similarly, in the plane just below it has 4 more face
centered atoms as its nearest neighbours
• Therefore the no. of nearest neighbours are :
4 + 4 + 4 = 12
Many of common metals (Cu,Ni,Pb..etc) crystallize in FCC
structure.
CrystalStructure

4 (0.353a)
FCC
0.74
CrystalStructure
Atomic Packing Factor of FCC

CrystalStructure
Atoms Shared Between: Each atom counts:
corner 8 cells 1/8
face centre 2 cells 1/2
body centre 1 cell 1
lattice type cell contents
P 1 [=8 x 1/8]
I 2 [=(8 x 1/8) + (1 x 1)]
F 4 [=(8 x 1/8) + (6 x 1/2)]
Unit cell contents
Counting the number of atoms within the unit cell

Introduction:
 The term “defect” or “imperfection” is generally used to describe any deviation from the
perfect periodic array of atoms in the crystal.
 The properties of some materials are extremely influenced by the presence of imperfections
such as mechanical strength, ductility, crystal growth, dielectric strength, condition in
semiconductors, which are termed structure-sensitive are greatly affected by the relatively
minor changes in crystal structure caused by defects or imperfections.
 There are some properties of materials such as stiffness, density and electrical conductivity
which are termed structure-insensitive, are not affected by the presence of defects in crystals.
 It is important to have knowledge about the types of imperfections that exist and the roles they
play in affecting the behavior of materials.
 Crystal imperfections can be classified on the basis of their geometry

0D
(Point defects)
CLASSIFICATION OF DEFECTS BASED ON DIMENSIONALITY
1D
(Line defects)
2D
(Surface / Interface)
3D
(Volume defects)
Vacancy
Impurity
Dislocation
Grain
boundary
Twins
Precipitate
Disclination
Frenkel
defect
Schottky
defect
Twin
boundary Voids /
Cracks
Stacking
faults Porosity
Inclusions

0D
(Point defects)
Impurity
Frenkel defect
Non-ionic
crystals
Interstitial
Substitutional
Point Defects
Schottky defect
Ionic
crystals
Imperfect point-like regions in the crystal about the size of 1-2 atomic
diameters
Other ~
It is a zero dimension defect, associated with one or two atomic positions.
Vacancy

Vacancy
Missing atom from an atomic site
Atoms around the vacancy displaced
Tensile stress field produced in the vicinity
Tensile Stress
Fields ?
Point Defects : Non-
ionic crystals
Interstitial
Impurity
Substitutional
Substitutional Impurity
• Foreign atom replacing the parent atom in the crystal
• E.g. Cu sitting in the lattice site of FCC-Ni
Interstitial Impurity
• Foreign atom sitting in the void of a crystal
• E.g. C sitting in the octahedral void in HT FCC-Fe
Relative size
Compressive Stress Fields Tensile Stress Fields

Point Defects : Ionic crystals
Frenkel Defect:
 To maintain the charge neutrality, a cation
vacancy-cation interstitial pair occur
together. This is called a Frenkel defect.
 The cation leaves its normal position and
moves to the interstitial site.
 There is no change in charge because the
cation maintains the same positive charge
as an interstitial.
E.g.AgI, CaF

Schottky Defect:
 Acation vacancy–anion vacancy pair known as a
Schottky defect.
 To maintain the charge neutrality, remove one
cation and one anion; this creates two vacancies.
E.g.Alkali halides

Effect of point imperfections:
 The presence of a point imperfection introduces distortions in the crystal.
 In the case of impurity atom, because of its difference in size, elastic
strains are created in the regions surrounding the impurity atom.
 All these factors tend to increase the potential energy of the crystal called
‘enthalpy’.
 The work done for the creation of such a point defect is called the
‘enthalpy of formation’of the point imperfection.

EDGE
1D Defects :
DISLOCATIONS
MIXED SCREW
 A dislocation is a linear or one-dimensional defect around which some of the
atoms are misaligned. The defects, which take place due to distortion of atoms
along a line, in some direction are called as ‘line defects.
 Line defects are also called dislocations.
 It is responsible for the phenomenon of slip by which most metals deform
plastically.

Edge dislocation:
• It is a linear defect that centers around the line that is
• defined along the end of the extra half-plane of atoms.
• The distorted configuration extends all along the edge into the crystal.
• Thus as the region of maximum distortion is centered around the
edge of the incomplete plane, this distortion represents a line
imperfection and is called an edge dislocation.
• Edge dislocations are represented by ‘’ or ‘T‘ depending on whether
the incomplete plane starts from the top or from the bottom of the
crystal.
• These two configurations are referred to as positive and

Burgers Vector
Crystal with edge dislocation
Edge dislocation
Perfect crystal
RHFS:
Right Hand Finish to Start convention
t vector
dislocation line vector
b vector
Direction of t
r
Direction of b
r

Edge Dislocation Glide
Shear stress
Surface
step

Edge Climb
Positive climb
Removal of a row of atoms
Negative climb
Addition of a row of atoms

Screw dislocation:
• In this dislocation, the atoms are displaced in
two separate planes perpendicular to each
other.
• It forms a spiral ramp around the dislocation.
• The Burgers Vector is parallel to the screw
dislocation line.
• Speed of movement of a screw dislocation is
lesser compared to edge dislocation.

Burgers Vector in Edge & Screw dislocations

Geometric properties of dislocations
Dislocation Property
Type of dislocation
Edge Screw
Relation between dislocation
line (t) and b
⊥
||
Slip direction || to b || to b
Direction of dislocation line
movement relative to b
||
⊥
Process by which dislocation
may leave slip plane
Glide/Climb Cross-slip

Mixed dislocations
b
t
P
Pu
ur
re
eEd
dg
ge
e
P
Pu
urre
es
sc
crre
ew
w
We are looking at the plane of the cut (sort of a
semicircle centered in the lower left corner). Blue
circles denote atoms just below, red circles atoms just
above the cut. Up on the right the dislocation is a pure
edge dislocation on the lower left it is pure screw. In
between it is mixed. In the link this dislocation is shown
moving in an animated illustration.

Surface imperfections:
• Surface imperfections arise from a change in the stacking of atomic planes on
or across a boundary.
• The change may be one of the orientations or of the stacking sequence of
atomic planes.
• In geometric concept, surface imperfections are two- dimensional. They are of
two types external and internal surface imperfections.
Surface imperfections (2D Defects)

External
Grain boundary
Low
angle
High
angle
2D Defects : Surface
defects
2D in a mathematical sense
The region of distortion is ~ few atomic diameters in thickness
Homophase
Heteropase
Twin Boundary
Stacking Faults
Internal
2D DEFECTS
(Surface / Interface)
Coherent Semi-coherent
Incoherent

External Surfaces:
 They are the imperfections represented by a boundary. At the boundary the
atomic bonds are terminated.
 Surface atoms are not bonded to the maximum number of nearest neighbors,
and are therefore in a higher energy state than the atoms at interior positions.
The bonds of these surface atoms that are not satisfied give rise to a surface
energy, expressed in units of energy per unit area (J/m2 or erg/cm2).

Grain Boundaries:
The boundary separating two small grains or
crystals having different crystallographic
orientations in polycrystalline materials.

Twin Boundaries:
A twin boundary is a special type of grain
boundary across which there is a specific mirror
lattice symmetry; that is, atoms on one side of the
boundary are located in mirror image positions of
the atoms on the other side.
The region of material between these boundaries
is appropriately termed a twin.
Twins result from atomic displacements that are
produced from applied mechanical shear forces
(mechanical twins), and also during annealing heat
treatments following deformation (annealing
twins).

Stacking Fault
Error in the sequence of stacking atomic planes → Stacking fault
Defined by a shift vector
…ABCABCABCABC…
FCC stacking
…ABCABABABC…
FCC stacking
with a stacking fault
Thin region of HCP type of stacking
In above the number of nearest neighbours remains the same
but next-nearest neighbours are different than that in FCC
Stacking fault energy ~ 0.01 – 0.05 J/m2
Stacking fault in HCP can lead to thin region of FCC kind of stacking

3D Defects : volume
defects
Volume ddeef
feeccttssin crystals aa
rr
eetthhrreeeedimensional aggregates o
o
f
fatoms or vacancies
Volume defects
Precipitates Dispersants Inclusions Voids (or pores)
PRECIPITATES
Precipitates are small particles that are introduced into the matrix by solid state
reactions. While precipitates are used for several purposes, their most common
purpose is to increase the strength of structural alloys by acting as obstacles to the
motion of dislocations. Their efficiency in doing this depends on their size, their
internal properties, and their distribution through the lattice. However, their role in the
microstructure is to modify the behavior of the matrix rather than to act as separate
phases in their own right.

3D Defects : volume
defects
DISPERSANTS
Dispersants are larger particles that behave as a second phase as well as influencing the
behavior of the primary phase. They may be large precipitates, grains, or polygranular particles
distributed through the microstructure. When a microstructure contains dispersants such
properties as mechanical strength and electrical conductivity are some average of the
properties of the dispersant phase and the parent.
INCLUSIONS
Inclusions are foreign particles or large precipitate particles. They are usually undesirable
constituents in the microstructure. For example, inclusions have a deleterious effect on the
useful strength of structural alloys since they are preferential sites for failure. They are also
often harmful in microelectronic devices since they disturb the geometry of the device by
interfering in manufacturing, or alter its electrical properties by introducing undesirable
properties of their own.
VOIDS (OR PORES)
Voids (or pores) are caused by gases that are trapped during solidification or by vacancy
condensation in the solid state. They are almost always undesirable defects. Their principal
effect is to decrease mechanical strength and promote fracture at small loads.

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