1. INDIAN INSTITUTE OF TECHNOLOGY ROORKEE
MATERIAL CHARACTERIZATION AND TESTING
Dr. Kaushik Pal
Professor
Department of Mechanical and Industrial Engineering
Indian Institute of Technology Roorkee
Lecture 01 : Introduction
2. 2
About Course
Subject Code: MIN:615 Course Title: Material Characterization and Testing
Contact Hours: L : 3 T : 1 P : 2/2
Examination Duration (Hrs.): Theory : 3 Practical : 0
Relative Weightage: CWS: 15-30 PRS: 20 MTE: 15-25 ETE:30-40
PRE: 0
Credits: 4 Semester: Autumn Subject Area: PCC
Pre-requisite: Nil
Objective: To give students a thorough and conceptual understanding of various material
characterization and testing techniques.
3. 3
S. No. Contents
Contact
Hours
1. Introduction: Engineering Materials, Properties of Materials; Crystal
Structure, Strengthening Mechanisms in Metals; Fundamentals of
Materials Characterization; Basic Sample Preparation and Interpretation of
Data.
03
2. Optical Microscopy: Fundamentals of Optics, Optical Microscope and
Image Formation, Depth of Field and Depth of Focus; Specimen
Preparation, Metallographic Principles, Applications.
05
3. Electron Microscopy: Scanning Electron Microscopy- Working Principle,
Electron Specimen Interaction, Instrumentation and Applications of SEM,
Chemical analysis in SEM (EDS & WDS), Electron Backscatter
Diffraction, Applications of EBSD; Transmission Electron Microscopy-
Instrument Details and Imaging Modes, Specimen Preparation Methods.
08
Course Content
4. 4
4. X-ray Diffraction: Properties of X-rays, Geometry of Crystals,
Bragg’s Law, Diffraction Methods, Intensity of Diffracted Beams,
Structure Factor Calculations, Diffractometer Measurement;
Applications of XRD- Phase Identification, Crystal Structure and
Phase Diagram Determination, Crystallite Size, and Lattice Parameter
Determination.
10
5. Thermal and Thermomechanical Methods: Thermal Gravimetric
Analysis (TGA), Differential Thermal Analysis (DTA), Differential
Scanning Calorimetry (DSC), and Dynamic Mechanical Analysis
(DMA), Thermomechanical Analysis (TMA).
09
6. Mechanical Testing: Uniaxial Tension Test, Compression Test, Three
and Four Point Bending Test, Hardness Tests, Impact Tests, Creep and
Stress Rupture Tests, Fatigue Test and Failure Analysis.
07
Total 42
5. 5
List of Experiments:
1. Sample preparation for optical and SEM observations.
2. Grain size determination of given metallic sample using optical microscopy.
3. Microstructural study and chemical analysis using SEM.
4. To demonstrate the TEM sample preparation and TEM analysis.
5. Determination of phases in multiphase powder sample using XRD.
6. DSC/DTA analysis.
7. To study dynamic mechanical behavior of polymers.
8. To determine the tensile properties of given samples.
9. To determine the hardness of given metallic sample by Brinell, Vickers, and Rockwell
hardness tester.
10. To determine the impact strength of given metallic sample by Izod and Charpy methods.
11. To perform fatigue test on given sample.
6. 6
• What is materials science?
• Why should we know about it?
• Materials drive our society
– Stone Age
– Bronze Age
– Iron Age
– Now?
• Silicon Age?
• Polymer Age?
Introduction
7. 7
Materials
• Over 70,000 different kinds and grades of engineering
materials
• This number grows daily
• 1,000 different materials make up an automobile
8. 8
Historical Perspective
• Earliest humans had access to only a very limited number
of materials, those that occur naturally:
Stone, wood, clay, skins, and so on.
• With time they discovered techniques for producing
materials that had properties superior to those of the
natural ones (pottery and various metals).
• Furthermore, it was discovered that the properties of a
material could be altered by heat treatments and by the
addition of other substances.
9. 9
• Metals:
– Strong, ductile
– High thermal & electrical conductivity
– Opaque, reflective
– e.g. aluminum, iron, and titanium
• Polymers/plastics: Covalent bonding sharing of electrons
– Soft, ductile, low strength, low density
– Thermal & electrical insulators
– Optically translucent or transparent
– e.g. acrylic, polyethylene, and nylon
Primary Classes of Materials
10. 10
• Ceramics: ionic bonding (refractory) – compounds of metallic &
non-metallic elements (oxides, carbides, nitrides, sulfides)
– Brittle, glassy, elastic
– Non-conducting (insulators)
– e.g. Al2O3, Fe3C, and SiC
Other “classes”:
• Composites
• Semiconductors (e.g. silicon, germanium)
11. 11
• Cast Iron
• Steel
– Mild steel, medium carbon steel, high carbon steel
• Specialty steel
– Stainless (tin plated or galvanized)
• Alloys (two or more pure metals)
– Steel= iron & carbon
– Brass= copper & zinc
– Bronze= copper & tin
Metals
14. 14
Composite Materials
Multiphase materials with measurable fraction of every phase
Obtained by artificial combination of different materials, so as to
attain properties that the individual components by themselves
cannot attain.
Composite materials are not the by-product of any chemical
reaction between two or more of its constituents.
Two major components in a composite:
I. Reinforcement (Discontinuous/dispersed
phase): Material that provide strength to
the matrix.
II.Matrix (Continuous phase): Material that
holds the reinforcement in place.
15. 15
Classification of Composite Materials:
Composite Material
Based on matrix material
Metal Matrix Composites
Polymer Matrix Composites
Ceramic Matrix Composites
Based on reinforcing material
structure
Particulate Composites
Fibrous Composites
Laminate Composites
16. 16
Naturally Occurring Composites:
Bone: Collagen fibers embedded in
hydroxyapatite matrix.
Wood: Cellulose fibers held together by
lignin matrix.
Man-made Composites:
Reinforced Concrete: Steel reinforcing
bars embedded in the concrete.
Fibrous Composites: Variety of fibers
(glass, Kevlar, carbon, nylon, etc.) bound
together by a polymeric matrix.
Cermets: Composite material composed of
ceramic and metal materials.
Examples:
19. 19
NonFerrous
Alloys
• Al Alloys
-low ρ: 2.7 g/cm3
-Cu, Mg, Si, Mn, Zn additions
-solid sol. or precip.
strengthened (struct.
aircraft parts
& packaging)
• Mg Alloys
-very low ρ: 1.7g/cm3
-ignites easily
-aircraft, missiles
• Refractory metals
-high melting T’s
-Nb, Mo, W, Ta
• Noble metals
-Ag, Au, Pt
-oxid./corr. resistant
• Ti Alloys
-relatively low ρ: 4.5 g/cm3
vs 7.9 for steel
-reactive at high T’s
-space applic.
• Cu Alloys
Brass: Zn is subst. impurity
(costume jewelry, coins,
corrosion resistant)
Bronze : Sn, Al, Si, Ni are
subst. impurities
(bushings, landing
gear)
Cu-Be :
precip. hardened
for strength
Nonferrous Alloys
20. 20
Ferrous Alloys
Iron-based alloys
• Steels
• Cast Irons
Types of Steels
• Steels- alloys of iron-carbon, may contain other alloying elements
• Several grades are available
• Low Alloy (<10 wt%)
– Low Carbon (<0.25 wt% C)
– Medium Carbon (0.25 to 0.60 wt% C)
– High carbon (0.60 to 1.4 wt% C)
• High Alloy
– Stainless Steel (>11 wt% Cr)
– Tool Steel
21. 21
Steels
Low Alloy High Alloy
low carbon
<0.25wt%C
Med carbon
0.25-0.6wt%C
high carbon
0.6-1.4wt%C
Uses auto
struc.
sheet
bridges
towers
press.
vessels
crank
shafts
bolts
hammers
blades
pistons
gears
wear
applic.
wear
applic.
drills
saws
dies
high T
applic.
turbines
furnaces
Very corros.
resistant
Example 1010 4310 1040 43 40 1095 4190 304, 409
Additions none
Cr,V
Ni, Mo
none
Cr, Ni
Mo
none
Cr, V,
Mo, W
Cr, Ni, Mo
plain HSLA plain
heat
treatable
plain tool stainless
Name
Hardenability 0 + + ++ ++ +++ varies
TS - 0 + ++ + ++ varies
EL + + 0 - - -- ++
increasing strength, cost, decreasing ductility
22. 22
• Four digit number
– First two give alloy
– Second two give wt%
carbon 100
– UNS number starts
with G
• Some alloy types
– 10XX, plain carbon
– 41XX, Cr + Mo
– 43XX, Ni + Cr + Mo
Low and Medium Carbon Steel Nomenclature
23. 23
• Tool steels
– High carbon content (0.6-1.4 wt. %)
– AISI code denoted by letter+number
• e.g. M1, A2, etc.
– UNS number starts with T
• Stainless steels
– >11 wt. % Cr
– 3XX series, austenitic
– 4XX series, ferritic and martensitic
– XX-XPH, precipitation hardened
– UNS number starts with S
Tool and Stainless Steel Nomenclature
24. 24
Types of Cast Iron
• Grey Cast Iron - Carbon as Graphite
• White Cast Iron - Carbides, Often Alloyed
• Ductile Cast Iron
o Nodular, Spheroidal Graphite
• Malleable Cast Iron
• Compacted Graphite Cast Iron
• CG Or Vermicular Iron
Cast Irons
Ferrous alloys with carbon content above 2.14 wt.%, and in addition other
alloying elements
Low melting – relatively easy to cast
Generally brittle
26. 26
What do these things do in steels?
Change C content
Mechanical work
Heat treat
Alloying elements
Change “structure”
Changing structure changes properties
27. 27
Components of Materials Engineering
• Materials science is the study of the relationships
between the structures and properties of materials.
• Materials engineering is the design or engineering of
a material to produce the desired properties.
Components of materials engineering:
28. 28
• Structure, processing, and properties are interrelated
Structure
Processing Properties
Fundamental Principle of Material Science
29. 29
• How do atoms assemble into solid structures?
• How does the density of a material depend on
its structure?
• When do material properties vary with the
sample (i.e., part) orientation?
The Structure of Crystalline Solids
30. 30
• Non dense, random packing
• Dense, ordered packing
Dense, ordered packed structures tend to have lower energies.
Energy and Packing
Energy
r
typical neighbor
bond length
typical neighbor
bond energy
Energy
r
typical neighbor
bond length
typical neighbor
bond energy
31. 31
• atoms pack in periodic, 3D arrays
Crystalline materials...
-metals
-many ceramics
-some polymers
• atoms have no periodic packing
Noncrystalline materials...
-complex structures
-rapid cooling
crystalline SiO2
noncrystalline SiO2
"Amorphous" = Noncrystalline
Materials and Packing
Si Oxygen
• typical of:
• occurs for:
32. 32
Metallic Crystal Structures
• How can we stack metal atoms to minimize empty
space?
2-dimensions
vs.
Now stack these 2-D layers to make 3-D structures
33. 33
• Tend to be densely packed.
• Reasons for dense packing:
- Typically, only one element is present, so all atomic
radii are the same.
- Metallic bonding is not directional.
- Nearest neighbor distances tend to be small in
order to lower bond energy.
- Electron cloud shields cores from each other
• Have the simplest crystal structures.
We will examine three such structures...
Metallic Crystal Structures
34. 34
• Rare due to low packing density (only Po has this structure)
• Close-packed directions are cube edges.
• Coordination # = 6
(# nearest neighbors)
Simple Cubic Structure (SC)
35. 35
• APF for a simple cubic structure = 0.52
APF =
a3
4
3
p (0.5a) 3
1
atoms
unit cell
atom
volume
unit cell
volume
Atomic Packing Factor (APF)
APF =
Volume of atoms in unit cell*
Volume of unit cell
*assume hard spheres
close-packed directions
a
R=0.5a
contains 8 x 1/8 =
1 atom/unit cell
36. 36
• Coordination # = 8
Adapted from Fig. 3.2,
Callister & Rethwisch 8e.
• Atoms touch each other along cube diagonals.
--Note: All atoms are identical; the center atom is shaded
differently only for ease of viewing.
Body Centered Cubic Structure (BCC)
ex: Cr, W, Fe (), Tantalum, Molybdenum
2 atoms/unit cell: 1 center + 8 corners x 1/8
37. 37
Atomic Packing Factor: BCC
a
APF =
4
3
p ( 3a/4 )3
2
atoms
unit cell atom
volume
a3
unit cell
volume
length = 4R =
Close-packed directions:
3 a
• APF for a body-centered cubic structure = 0.68
a
R
a
2
a
3
38. 38
• Coordination # = 12
• Atoms touch each other along face diagonals.
--Note: All atoms are identical; the face-centered atoms are shaded
differently only for ease of viewing.
Face Centered Cubic Structure (FCC)
ex: Al, Cu, Au, Pb, Ni, Pt, Ag
4 atoms/unit cell: 6 face x 1/2 + 8 corners x 1/8
39. 39
• APF for a face-centered cubic structure = 0.74
Atomic Packing Factor: FCC
maximum achievable APF
APF =
4
3
p ( 2a/4 )3
4
atoms
unit cell atom
volume
a3
unit cell
volume
Close-packed directions:
length = 4R = 2 a
Unit cell contains:
6 x1/2 + 8 x1/8
= 4 atoms/unit cell
a
2 a
40. 40
A sites
B B
B
B
B
B B
C sites
C C
C
A
B
B sites
• ABCABC... Stacking Sequence
• 2D Projection
• FCC Unit Cell
FCC Stacking Sequence
B B
B
B
B
B B
B sites
C C
C
A
C C
C
A
A
B
C
41. 41
• Coordination # = 12
• ABAB... Stacking Sequence
• APF = 0.74
• 3D Projection • 2D Projection
Hexagonal Close-Packed Structure (HCP)
6 atoms/unit cell
ex: Cd, Mg, Ti, Zn
• c/a = 1.633
c
a
A sites
B sites
A sites Bottom layer
Middle layer
Top layer
42. 42
Theoretical Density
where n = number of atoms/unit cell
A = atomic weight
VC = Volume of unit cell = a3 for cubic
NA = Avogadro’s number
= 6.022 x 1023 atoms/mol
Density = =
VCNA
n A
=
Cell
Unit
of
Volume
Total
Cell
Unit
in
Atoms
of
Mass
43. 43
• Ex: Cr (BCC)
A = 52.00 g/mol
R = 0.125 nm
n = 2 atoms/unit cell
theoretical
a = 4R/ 3 = 0.2887 nm
actual
=
a3
52.00
2
atoms
unit cell
mol
g
unit cell
volume atoms
mol
6.022x1023
Theoretical Density
= 7.18 g/cm3
= 7.19 g/cm3
a
R
44. 44
Densities of Material Classes
metals > ceramics > polymers
Why?
(g/cm
)
3
Graphite/
Ceramics/
Semicond
Metals/
Alloys
Composites/
fibers
Polymers
1
2
20
30
*GFRE, CFRE, & AFRE are Glass,
Carbon, & Aramid Fiber-Reinforced
Epoxy composites (values based on
60% volume fraction of aligned fibers
in an epoxy matrix).
10
3
4
5
0.3
0.4
0.5
Magnesium
Aluminum
Steels
Titanium
Cu,Ni
Tin, Zinc
Silver, Mo
Tantalum
Gold, W
Platinum
Graphite
Silicon
Glass -soda
Concrete
Si nitride
Diamond
Al oxide
Zirconia
HDPE, PS
PP, LDPE
PC
PTFE
PET
PVC
Silicone
Wood
AFRE *
CFRE *
GFRE*
Glass fibers
Carbon fibers
Aramid fibers
Metals have...
• close-packing
(metallic bonding)
• often large atomic masses
Ceramics have...
• less dense packing
• often lighter elements
Polymers have...
• low packing density
(often amorphous)
• lighter elements (C,H,O)
Composites have...
• intermediate values
In general
45. 45
• Mechanical
• Electrical
• Thermal
• Magnetic
• Optical
What are some general categories of properties
of engineering materials?
47. 47
Electrical Properties
• Electrical Resistivity of Copper:
• Adding “impurity” atoms to Cu increases resistivity.
• Deforming Cu increases resistivity.
T (°C)
-200 -100 0
1
2
3
4
5
6
Resistivity,
ρ
(10
-8
Ohm-m)
0
48. 48
Thermal Properties
• Space Shuttle Tiles:
-- Silica fiber insulation
offers low heat conduction.
• Thermal Conductivity
of Copper:
-- It decreases when
you add zinc!
Composition (wt% Zinc)
Thermal
Conductivity
(W/m-K)
400
300
200
100
0
0 10 20 30 40
49. 49
Magnetic Properties
• Magnetic Permeability
vs. Composition:
-- Adding 3 atomic % Si
makes Fe a better
recording medium!
• Magnetic Storage:
-- Recording medium
is magnetized by
recording head.
Magnetic Field
Magnetization
Fe+3%Si
Fe
50. 50
• Transmittance:
o Aluminum oxide may be transparent, translucent, or opaque
depending on the material’s structure (i.e., single crystal vs.
polycrystal, and degree of porosity).
Single Crystal
Polycrystal:
No Porosity
Polycrystal:
Some Porosity
Optical Properties
51. 51
Deformation & Strengthening Mechanisms
• Materials experience two kinds of deformation:
1. Elastic deformation
2. Plastic deformation
• Elastic deformation:
o involves temporary stretching or bending of the bonds between atoms, but
the atoms do not slip past each other.
• Plastic deformation:
o Permanent deformation; strength and hardness are measures of a
material’s resistance to this deformation.
o On a microscopic scale, plastic deformation corresponds to the net
movement of large numbers of atoms in response to an applied stress.
o During this process, interatomic bonds must be ruptured and then
reformed.
o In crystalline solids, plastic deformation most often involves the motion of
dislocations, linear crystalline defects
53. 53
Dislocation Motion & Plastic Deformation
• Metals – plastic deformation occurs by slip – an edge
dislocation (extra half-plane of atoms) slides over adjacent
plane half-planes of atoms.
• If dislocations can't move,
plastic deformation doesn't occur!
54. 54
Dislocation Motion
• A dislocation moves along a slip plane in a slip direction
perpendicular to the dislocation line
• The slip direction is the same as the Burgers vector direction
Edge dislocation
screw dislocation
55. 55
Slip System
– Slip Plane - plane on which easiest slippage occurs
• Highest planar densities (and large interplanar spacings)
– Slip Directions - directions of movement
• Highest linear densities
Deformation Mechanisms
– FCC Slip occurs on {111} planes (close-packed) in <110>
directions (close-packed)
=> total of 12 slip systems in FCC
– For BCC & HCP there are other slip systems.
56. 56
Stress and Dislocation Motion
• Resolved shear stress, 𝜏𝑅
– results from applied tensile stresses
slip plane
normal, ns
Resolved shear
stress: τR =Fs /As
AS
τR
τR
FS
Relation between
σ and τR
τR =FS /AS
F cos λ A/cos ϕ
λ
F
FS
ϕ
nS
AS
A
Applied tensile
stress: = F/A
σ
F
A
F
cos
cos
R
57. 57
• Condition for dislocation motion: CRSS
R
• Ease of dislocation motion depends
on crystallographic orientation
10-4 GPa to 10-2 GPa
typically
cos
cos
R
Critical Resolved Shear Stress
maximum at = = 45º
τR = 0
λ = 90°
σ
τR = σ/2
λ = 45°
ϕ = 45°
σ
τR = 0
ϕ= 90°
σ
59. 59
Example: Deformation of single crystal
So the applied stress of 45 MPa will not cause the crystal to
yield.
= 35°
= 60°
τcrss = 20.7 MPa
a) Will the single crystal yield?
b) If not, what stress is needed?
σ = 45 MPa
MPa
7
.
20
MPa
4
.
18
)
41
.
0
(
MPa)
45
(
)
60
)(cos
35
cos
(
MPa)
45
(
crss
60. 60
MPa
0.5
5
41
.
0
MPa
0.7
2
cos
cos
crss
y
Example: Deformation of single crystal
What stress is necessary (i.e., what is the yield
stress, σy)?
)
41
.
0
(
cos
cos
7
.
20
crss y
y
MPa
MPa
5
.
50
y
So for deformation to occur the applied stress must be
greater than or equal to the yield stress.
61. 61
Four Strategies for Strengthening:
1: Reduce Grain Size
• Grain boundaries are barriers to slip.
• Barrier "strength“ increases with
increasing angle of misorientation.
• Smaller grain size: more barriers to
slip.
2
/
1
0
d
ky
yield
Hall-Petch Equation:
62. 62
Four Strategies for Strengthening:
2: Form Solid Solutions
• Smaller substitutional
impurity
Impurity generates local stress at A and
B that opposes dislocation motion to the
right.
A
B
• Larger substitutional
impurity
Impurity generates local stress at C and
D that opposes dislocation motion to the
right.
C
D
• Impurity atoms distort the lattice & generate lattice strains.
• These strains can act as barriers to dislocation motion.
64. 64
Example: Solid Solution Strengthening in Copper
• Tensile strength & yield strength increase with wt% Ni.
• Empirical relation:
• Alloying increases σy and TS.
2
/
1
~ C
y
Tensile
strength
(MPa)
wt.% Ni, (Concentration C)
200
300
400
0 10 20 30 40 50
Yield
strength
(MPa) wt.%Ni, (Concentration C)
60
120
180
0 10 20 30 40 50
65. 65
• Hard precipitates are difficult to shear.
Example: Ceramics in metals (SiC in Iron or Aluminium).
• Result:
S
y
1
~
Four Strategies for Strengthening:
3: Precipitation Strengthening
Large shear stress needed
to move dislocation toward
precipitate and shear it.
Dislocation
“advances” but
precipitates act as
“pinning” sites with
S .
spacing
Side View
precipitate
Top View
Slipped part of slip plane
Unslipped part of slip plane
S
spacing
66. 66
Four Strategies for Strengthening:
4: Cold Work (Strain Hardening)
• Deformation at room temperature (for most metals).
• Common forming operations reduce the cross-sectional area:
-Forging
Ao Ad
force
die
blank
force
-Drawing
tensile
force
Ao
Ad
die
die
-Extrusion
ram billet
container
container
force
die holder
die
Ao
Ad
extrusion
100
x
%
o
d
o
A
A
A
CW
-Rolling
roll
Ao
Ad
roll
67. 67
• Dislocation structure in Ti after cold working.
• Dislocations entangle
with one another
during cold work.
• Dislocation motion
becomes more difficult.
Dislocation Structures Change During Cold Working
68. 68
Fundamentals of Materials Characterization
• Definition of Material Characterization:
“Characterization describes those features of a composition
and structure (including defects) of a material that are
significant for a particular preparation, study of properties, or
use, and suffice for the reproduction of the material”
• Two main aspects of the material characterization:
Accurately measuring the physical and chemical properties of materials.
Accurately measuring (determining) the structure of a material (Atomic
level structure and microscopic level structure)
• Mechanical, electrical, magnetic and optical properties of a
material are strongly dependent on its structural characteristics.
69. 69
Sample Preparation in Characterization
• Preliminary (and important) step in material characterization
• Before samples can be analysed using advanced scientific
equipment and instruments, they must be properly treated and
prepared.
• It is an important stage of the overall analysis process as it helps
to:
o prevent contamination
o improve accuracy
o minimize the risk of results distortion
• Almost always, sample preparation starts with extraction -
isolating a representative piece of material from a larger source.
