Title: BMFB 3263: Materials Characterization
1BMFB 3263 Materials Characterization
Dr. Mohd Warikh Bin Abd Rashid Room 2nd Floor,
PFI, Block B Email warikh_at_utem.edu.my
2- 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!!!!
3Learning 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.
4Course Structure
5Course Synopsis
- 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.
6- 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
7Topic 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
8Why 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.
9Space Shuttle Columbia Disaster 2003
10The 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
11(No Transcript)
12Risk Management
- 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.
13If you are given these materials, how do you
inspect their properties???
14Introduction
- Material characterization
- Physical method
- Mechanical tests
- Chemical analysis
- Thermal analysis
- Non-destructive evaluation
- Physical
- Microstructural evaluation
- X-Ray Diffraction (XRD)
- X-Ray Fluorescence Spectroscopy (XRF)
- Mass Spectroscopy
- FTIR spectroscopy.
15- Mechanical tests
- Tensile
- Compression
- Creep
- Fatigue
- Chemical analysis
- Atomic Absorption Spectroscopy (AAS)
- functional group analysis.
- Thermal analysis
- Differential thermal analysis (DTA)
- Differential Scanning Calorimetry (DSC )
- Thermogravimetry Analysis (TGA )
- Dynamic Mechanical analysis (DMA), etc.
16- Non-Destructive Testing (NDT)
- Ultrasound
- Radiology
- liquid penetrant
- Eddy current, etc.
17Material Characterization
- 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.
18Material Properties
- 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.
19Microstructure Characterization
- 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.
20Microstructure Characterization
- Achieved by allowing some form of probe to
interact carefully on prepared specimen. - Probe visible light (optical microscope), X-ray
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.
21Microstructure Evaluation
- 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).
22Microstructure Evaluation
- 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.
23Optical microscope
24Optical Microscope
- 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.
25Optical Microscope
- 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 lt 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.
26Optical Microscope
Principle components of reflection optical
microscope
27Optical Microscope
- 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.
28Optical Microscope
- Numerical aperture, NA important characteristic
of objective lens system, µ sin a. - 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.
29Optical Microscope
- 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.
30(i)
(ii)
- Cu-4Ti cast, cold worked aged.
- Cu-5Ni-2.5Ti cast, cold worked aged.
- high N2, high Mn, austenitic stainless steel.
(iii)
31Optical Microscope
- Common magnification 10x 1500x, resolution
limit about 0.2 microns. - Imaging modes transmitted reflected light,
polarized light, bright-field, dark field,
differential interference contrast, and phase
contrast. - In transmission mode, thickness no more than 5
microns.
32How to prepare samples for optical microscopy
observation?
33How to prepare metal sample for optical
microscope observation??
34Sample preparation for metal
Cut the sample
Mounting in resin
Grinding with SiC paper
Lapping
Polishing
Etching
35- Cutting a specimen
- Specimen 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.
36- Mounting
- Mounting of specimens
- necessary to allow them to be handled easily.
- Minimise the amount of damage likely to be caused
to the specimen itself. - Mounting material
- 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 150C) 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 - to prevent grit, polishing media or etchant being
trapped in the pores, and to preserve the open
structure of the material.
37- 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.
38- 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,
- 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.
39180 grit
400 grit
1200 grit
800 grit
Copper specimen after series of grinding
40- 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
41- Polishing
- Polishing discs are covered with soft cloth
impregnated with abrasive diamond particles and
an oily lubricant. - Particles of two different grades are used
- 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 1 micron level.
Ideally there should be no scratches after
polishing, but it is often hard to completely
remove them all.
Copper specimen polished to 6 micron level
42- Etching
- 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)
43- 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
Over etched copper specimen
Etched copper specimen
44Effect of Etching
Etched Steel 200 X
Unetched Steel 200 X
Unetched Brass 200 X
Etched Brass 200 X
45- 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. - 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 - 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
46Ceramic 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.
47Polymer Samples
- Thin sections
- 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. - 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. - The thickness of cut slices of polymer tends to
lie in the range 2 to 30 mm depending on the type
of material. - Harder polymers can be prepared in the same way
as thin ceramic specimens. - Polished sections
- These are prepared in the same way as
metallographic specimens. - 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. - As crystalline regions are attacked more slowly
than amorphous ones, etching of polymer specimens
can produce contrast revealing the polymer
structure.