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BMFB 3263: Materials Characterization

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BMFB 3263: Materials Characterization Dr. Mohd Warikh Bin Abd Rashid Room: 2nd Floor, PFI, Block B Email: warikh_at_utem.edu.my * Sample preparation for metal ... – PowerPoint PPT presentation

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Title: BMFB 3263: Materials Characterization


1
BMFB 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!!!!

3
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.

4
Course Structure
5
Course 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

7
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

8
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.

9
Space Shuttle Columbia Disaster 2003
10
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
11
(No Transcript)
12
Risk 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.

13
If you are given these materials, how do you
inspect their properties???
14
Introduction
  • 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.

17
Material 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.

18
Material 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.

19
Microstructure 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.

20
Microstructure 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.

21
Microstructure 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).

22
Microstructure 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.

23
Optical microscope
24
Optical 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.

25
Optical 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.

26
Optical Microscope
Principle components of reflection optical
microscope
27
Optical 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.

28
Optical 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.

29
Optical 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)
  1. Cu-4Ti cast, cold worked aged.
  2. Cu-5Ni-2.5Ti cast, cold worked aged.
  3. high N2, high Mn, austenitic stainless steel.

(iii)
31
Optical 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.

32
How to prepare samples for optical microscopy
observation?
33
How to prepare metal sample for optical
microscope observation??
34
Sample 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.

39
180 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
44
Effect 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
46
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.

47
Polymer 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.
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