Transcript EBB 333 PENCIRIAN BAHAN KEJURUTERAAN

BMFB 3263: Materials
Characterization
Dr. Mohd Warikh Bin Abd Rashid
Room: 2nd Floor, PFI, Block B
Email: [email protected]
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OBE – Outcome Based Education.
 Student-centered learning rather than
lecture based.
 Active Learning (AL) - Students actively
involved in the learning process. Learners
activity in class.
 Please read before coming to class!!!!
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Learning Outcomes
1. Explain the fundamental of materials characterization including the
theory, working principle and application.
2. Analyze the materials characterization results qualitatively and
quantitatively.
3. Summarize material characteristics based on its characterizations
results.
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Course Structure
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Course Synopsis :
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This course will discuss about material characterization
techniques from the theoretical aspect, instrumentations
and applications.
The techniques include:
 Microstructural Analysis (optical microscope, SEM,
TEM and SPM) and
 Thermal Analysis (TGA, DTA, DSC, DTMA and
TMA).
Case studies and example will be given for each technique
to show how these methods are used to characterize
engineering materials.
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References:
Refer to Teaching Plan
 Materials Characterization: Introduction To Microscopic
and Spectroscopic Methods, Yang Leng, John Wileys &
Sons
 Microstructural Characterization of Materials by David
Brandon and Wayne D. Kaplan, John Wileys & Sons
 Database: www.sciencedirect.com
 Internet
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Topic Outcomes:
By the end of this topic, you should be:
 able to understand the importance of materials
characterization for materials engineers
 able to list down types of materials characterization
 know the concept of microstructure and evaluation
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Why do you think materials
characterization is important
for materials engineer?
In 5 minutes, discuss with 1-2
persons next to you, and write
down on a piece of paper.
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Space Shuttle Columbia Disaster
2003
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The loss of the Columbia was a result of
damage sustained during launch when
a piece of foam insulation the size of a
small briefcase broke off the Space
Shuttle external tank (the main
propellant tank) under the aerodynamic
forces of launch. The debris struck the
leading edge of the left wing, damaging
the Shuttle's thermal protection system
(TPS). While Columbia was still in orbit,
some engineers suspected damage, but
NASA managers limited the
investigation on the grounds that little
could be done even if problems were
found
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Risk Management
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NASA management failed to recognize the
relevance of engineering concerns for
safety
 failure
to honour engineer requests for
imaging to inspect possible damage
 failure to respond to engineer requests about
status of astronaut inspection of the left wing.
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If you are given these materials, how
do you inspect their properties???
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Introduction
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Material characterization
 Physical
method
 Mechanical tests
 Chemical analysis
 Thermal analysis
 Non-destructive evaluation
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Physical
 Microstructural
evaluation
 X-Ray Diffraction (XRD)
 X-Ray Fluorescence Spectroscopy (XRF)
 Mass Spectroscopy
 FTIR spectroscopy.
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Mechanical tests
 Tensile
 Compression
 Creep
 Fatigue
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Chemical analysis
 Atomic
Absorption Spectroscopy (AAS)
 functional group analysis.
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Thermal analysis
 Differential
thermal analysis (DTA)
 Differential Scanning Calorimetry (DSC )
 Thermogravimetry Analysis (TGA )
 Dynamic Mechanical analysis (DMA), etc.
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Non-Destructive Testing (NDT)
 Ultrasound
 Radiology
 liquid
penetrant
 Eddy current, etc.
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Material Characterization
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1.
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4.
5.
6.
Analysis depends on
 application
 intended use.
Examples:
Materials used for high Temperature: corrosion, optical
field, structural etc.
Polymer : Tg point, curing T, degradation T, degree of
crystallinity.
Compound: melting point, phase transformation.
Magnetic material: Curie T.
Non-destructive Testing (NDT) – checking without affecting
usefulness. Usually inspection to finish product.
New materials – thorough characterization.
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Material Properties
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Mechanical – not a unique function of a material but
valued from test pieces e.g. response from certain
mechanical loading. Tensile strength (yield & UTS),
modulus, fatigue, creep.
Physical – unique properties of material. Density,
thermal, electrical, magnetic and optical properties.
Thermal – thermal expansion (CTE), thermal
conductivity, specific heat & thermal diffusivity.
Electrical – conductivity, thermoelectricity, charge
storing capacity, dielectric loss.
Optical – refractive index, transparency, colour, etc.
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Microstructure Characterization
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Visually observable – limited range of wavelength & limited
resolution.
Optical microscope – 1000x magnification.
TEM – wavelength of energetic electrons much lesser than
interplanar spacing in crystal  potentially able to resolve
crystal lattice.
SEM – usually limited by inelastic scattering under probe, & is
the order of few nanometers for secondary electrons.
Resolution depends on focus of electron beam into fine probe,
but beam current available decreases.
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Microstructure Characterization
Achieved by allowing some form of probe to
interact carefully on prepared specimen.
 Probe – visible light (optical microscope), Xray radiation (EDX, XRD) & high energy
electron beams (electron microscopy).
 Resolution – ability to distinguish closely
spaced features. Determined by wavelength of
probe radiation, characteristic of interaction, &
nature of image-forming system.
 Shorter wavelength & wider acceptance angle
of imaging system – better resolution.
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Microstructure Evaluation
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Microstructure – identical arrangement in 3-D space
of atoms & all types of non-equilibrium defects.
Very important since microstructure often affects
properties. E.g different phases (diff. microstructure)
in steel / iron give different properties ; pearlite,
bainite & martensite.
Fracture surface, failure initiation point, defects such
as pores, grain size, particle distribution & many
other features can be examined.
Parameters – qualitative (shape, distribution, colour)
& quantitative (grain size, % of second phase,
dislocation density).
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Microstructure Evaluation
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Grain size – DV, DA, DL, DASTM.
Dv – average number of grains in a unit vol.
DA – average number of grains intercepted per unit
area.
DL – mean linear intercept. DASTM – compare sample
microstructure with ASTM Grain-size Charts.
Phase volume fraction – length of line traversing 2nd
phase relative to total length. Also random grid of test
points.
Optical – info obtained thru light (visible light)
transmitted or reflected from matter.
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Optical microscope
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Optical Microscope
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Sample & sectioning – often best to have samples
from more that one orientation.
E.g rolled part – sections taken perpendicular to all 3 ;
rolling direction, transverse & thru-thickness.
Casting – differences in cooling rate & effects of
segregation.
Mounting, grinding & polishing – prepare surface to
be flat, devoid of topographical features unrelated to
bulk microstructure of sample.
Polishing – mechanical, chemical & electrochemical.
Etching – selective removal of material from surface
in order to develop surface features – microstructure.
Develop topography – grooving grain boundaries.
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Optical Microscope
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Reflection – only surface is imaged, topology and any
other features which give contrast.
Transmission – very thin specimen. In med science,
bio tissues. Geology, mineral specimen thickness < 50
micron, polarized light frequently give contrast &
provides info on optical properties and spatial
orientation of the crystalline phases.
Metallurgical samples – reflection, Polymer – either
method, Ceramic & Semiconductor – reflection.
Specimen preparation – important to have good
preparation to get successful image.
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Optical Microscope
Principle
components of
reflection
optical
microscope
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Optical Microscope
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3 separate system – illuminating system, specimen
stage & imaging system.
Condenser lens – focus an image of the source.
Condenser aperture – limits amount of light from
source.
Virtual-image aperture – ensure light is not internally
reflected within m/scope, leading to unwanted
background intensity.
Objective lens – performance depends on its
numerical aperture (NA). Not only resolution, but
brightness also depends on NA.
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Optical Microscope
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Numerical aperture, NA – important characteristic of
objective lens system, µ sin α.
Working distance of objective lens from specimen
surface decreases dramatically as NA is increased.
Specially designed long-working-distance lenses allow
specimen to be imaged in hostile environment –
corrosive medium, elevated or cryogenic T.
Image magnification by objective lens is insufficient
to be fully resolvable by human eye – insert eyepiece,
additional lens to focus on light-sensitive,
photographic emulsion, or scan image in tv raster and
display on monitor.
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Optical Microscope
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Or different height of neighbouring grain surface.
Different phases (second phases, reinforcement,
inclusion, etc).
Thermal etching – usually for material which inert to
chemical attack in etching.
Image contrast – developed thru proper polishing and
etching.
Most metals absorb significant portion of incident
light. E.g Cu & gold absorb blue, so reflected light
appear reddish or yellow.
Angle of incidence – reflected, transmitted or
absorbed.
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(i)
(ii)
(i) Cu-4Ti : cast, cold worked
& aged.
(ii) Cu-5Ni-2.5Ti : cast, cold
worked & aged.
(iii)
(iii) high N2, high Mn,
austenitic stainless steel.
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Optical Microscope
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Common magnification 10x –
1500x, resolution limit about 0.2
microns.
Imaging modes – transmitted &
reflected light, polarized light, brightfield, dark field, differential
interference contrast, and phase
contrast.
In transmission mode, thickness no
more than 5 microns.
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How to prepare samples for optical
microscopy observation?
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How to prepare metal sample for
optical microscope observation??
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Sample preparation for metal
Cut the sample
Mounting in resin
Grinding with
SiC paper
Etching
Polishing
Lapping
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
Cutting a specimen
 Specimen
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from a larger piece of material
ensure that it is representative of the features found in
the larger sample
it contains all the information required to investigate a
feature of interest.
 Problem:
preparation of the specimen could change
the microstructure of the material e.g. through
heating, chemical attack, or mechanical damage. The
amount of damage depends on the method by which
the specimen is cut and the material itself.
 Cutting with abrasives → high amount of damage
 Cutting with low-speed diamond saw → lessen the
problems.
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Mounting
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Mounting of specimens:
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necessary to allow them to be handled easily.
Minimise the amount of damage likely to be caused to the specimen
itself.
Mounting material
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not influence the specimen as a result of chemical reaction or
mechanical stresses.
should adhere well to the specimen
if the specimen is to be electropolished later in the preparation then
the mounting material should also be electrically conducting.

Hot mounting: (about 150°C) using a mounting press
either in a thermosetting plastic, e.g. phenolic resin, or a
thermosoftening plastic e.g. acrylic resin.
 Cold mounting: e.g. epoxy, acrylic or polyester resin.
 Porous materials must be impregnated by resin before
mounting or polishing
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to prevent grit, polishing media or etchant being trapped in the
pores, and to preserve the open structure of the material.
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A
mounted specimen usually has a thickness
of about half its diameter, to prevent rocking
during grinding and polishing.
 The edges of the mounted specimen should
also be rounded to minimise the damage to
grinding and polishing discs.
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Grinding
 Grinding- remove surface layers damaged by cutting
 Mounted specimens are ground with rotating discs of abrasive
paper, for example wet silicon carbide paper → COARSER to
FINER.
 The coarseness of the paper is indicated by a number: the number
of grains of silicon carbide per square inch. So, for example, 180
grit paper is coarser than 1200.
 The grinding procedure involves several stages,
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using a finer paper (higher number) each time.
Each grinding stage removes the scratches from the previous coarser
paper.
Easily achieved by orienting the specimen perpendicular to the previous
scratches.
Between each grade the specimen is washed thoroughly with soapy
water to prevent contamination from coarser grit present on the
specimen surface.
Typically, the finest grade of paper used is the 1200, and once the only
scratches left on the specimen are from this grade, the specimen is
thoroughly washed with water, followed by alcohol and then allowed to
dry. The drying can be made quicker using a hot air drier.
Cleaning specimens in an ultrasonic bath can also be helpful, but is
not essential.
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180 grit
400 grit
1200 grit
800 grit
Copper specimen after series of grinding
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Lapping
 The
lapping process is an alternative to grinding, in
which the abrasive particles are not firmly fixed to
paper.
 Lapping process: applied a paste and lubricant to the
surface of a disc.
 Surface roughness from coarser preparation steps is
removed by the micro-impact of rolling abrasive
particles.
Lapping machine
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Polishing
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Polishing discs are covered with soft cloth impregnated
with abrasive diamond particles and an oily lubricant.
 Particles of two different grades are used :
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a coarser polish - typically with diamond particles 6 microns in
diameter: remove the scratches produced from the finest grinding
stage
finer polish – typically with diamond particles 1 micron in diameter,
to produce a smooth surface. Before using a finer polishing wheel
the specimen should be washed thoroughly with warm soapy water
followed by alcohol to prevent contamination of the disc.
Copper specimen polished to
6 micron level
Copper specimen
polished to 1 micron
level. Ideally there
should be no
scratches after
polishing, but it is often
hard to completely
remove them all.
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Etching
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Etching is used to reveal the microstructure of the metal through
selective chemical attack.
In alloys with more than one phase: etching creates contrast
between different regions through differences in topography or
the reflectivity of the different phases.
The rate of etching is affected by crystallographic orientation, so
contrast is formed between grains, for example in pure metals.
The reagent will also preferentially etch high energy sites such
as grain boundaries. This results in a surface relief that enables
different crystal orientations, grain boundaries, phases and
precipitates to be easily distinguished.
The specimen is etched using a reagent. For example,
 etching stainless steel or copper and its alloys: a saturated
aqueous solution of ferric chloride, containing a few drops of
hydrochloric acid is used. This is applied using a cotton bud
wiped over the surface a few of times The specimen should
then immediately be washed in alcohol and dried.
 metal: Nital 5-10% (nitric acid in alcohol)
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 Following
the etching process there may be
numerous small pits present on the surface. These
are etch pits caused by localised chemical attack, and
in most cases they do not represent features of the
microstructure. They may occur preferentially in
regions of high local disorder, for example where
there is a high concentration of dislocations.
 If the specimen is over etched, ie. etched for too long,
these pits tend to grow, and obscure the main
features to be observed - as seen in the images
below:
Etched copper specimen
Over etched copper specimen
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Effect of Etching
Unetched
Steel
200 X
Etched
Steel
200 X
Unetched
Brass
200 X
Etched
Brass
200 X
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Surface requirement:
 Flat
and level.
 If not, then as the viewing area is
moved across the surface it will
pass in and out of focus.
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In addition, it will make it difficult to
have the whole of the field of view in
focus - while the centre is focused, the
sides will be out of focus.
Use a specimen levelling press –
overcome this problem
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Press the mounted specimen into
plasticene on a microscope slide,
making it level.
Use a small piece of paper or cloth
covers the surface of the specimen
to avoid scratching.
Specimen levelling
press
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Ceramic Samples
Thin Sections

To prepare ceramic specimens, a thin slice, approximately 5 mm thick,
is cut using a diamond saw or cutting wheel.
 One surface is then lapped using liquid suspensions of successively
finer silicon carbide powders. Between stages in the process the
specimen must be thoroughly cleaned. After final washing and drying
the ground surface is bonded to a microscope slide with resin.
 A cut off saw is used on the exposed face to reduce the thickness to
about 0.7 mm. The specimen is then lapped to take it to the required
thickness – usually about 30 mm, although some ceramic specimens
are thinned to as little as 10 mm, due to their finer grain size. The slide
is checked for thickness under the microscope, and then hand finished.
Polished sections
 These differ from ordinary thin sections in that the upper surface of
the specimen is not covered with a cover slip, but is polished. Care
must be taken to prevent the specimen breaking. Sections may be
examined using both transmitted and reflected light microscopy,
which is particularly useful if some constituents are opaque.
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Polymer Samples
Thin sections
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Thin sections of organic polymers are prepared from solid material by cutting slices
using a microtome. They must be cut at a temperature below the glass transition
temperature of the polymer.
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A cut section curls up during cutting and must be unrolled and mounted on a
microscope slide and covered with a cover slip. A few drops of mounting adhesive
wet the specimen and must be compatible with it. The mounting temperature must
not affect the microstructure of the specimen.
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The thickness of cut slices of polymer tends to lie in the range 2 to 30 mm depending
on the type of material.
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Harder polymers can be prepared in the same way as thin ceramic specimens.
Polished sections
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These are prepared in the same way as metallographic specimens.
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Elastomers are more difficult to polish than thermosetting polymers and require
longer polishing times. Lubricants used during polishing must not be absorbed by the
specimen.
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As crystalline regions are attacked more slowly than amorphous ones, etching of
polymer specimens can produce contrast revealing the polymer structure.
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