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
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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

• 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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(No Transcript)
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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.

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If you are given these materials, how do you
inspect their properties???
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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.

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• 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.

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• Non-Destructive Testing (NDT)
• Ultrasound
• Radiology
• liquid penetrant
• Eddy current, etc.

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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.

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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.

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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.

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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.

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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).

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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.

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Optical microscope
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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.

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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.

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Optical Microscope
Principle components of reflection optical
microscope
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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.

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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.

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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.

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(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)
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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.

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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
Lapping
Polishing
Etching
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• 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.

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• 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.

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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,
• 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
• 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
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• 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)

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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

Over etched copper specimen
Etched copper specimen
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Effect of Etching
Etched Steel 200 X
Unetched 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.
• 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
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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
• 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.