Handbook of Analytical Methods for Materials Copyright © 2001 by Materials Evaluation and Engineering, Inc.
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LIGHT MICROSCOPY
DESCRIPTION OF TECHNIQUE
Light microscopy in materials analysis generally refers to reflected light microscopy. In this method,
light is directed vertically through the microscope objective and reflected back through the objective
to an eyepiece, view screen, or camera. Transmitted light is occasionally used for transparent and
translucent materials. For some low-magnification work (stereo microscopy), external, oblique
illumination can be reflected off the sample into the objective.
Magnification of the sample image is obtained by light refraction
through a combination of objective lenses and eyepieces. The
minimum feature resolution is approximately 0.2 µm. However,
smaller features - as small as about 0.05 µm - can be detected
by image contrast enhancement with polarized light, interference
contrast, and dark field illuminations. The resulting images can be
recorded either on traditional films or as digital files for computer
display, analysis, and storage.
ANALYTICAL INFORMATION
Bright Field Light Microscopy - This method produces true color images at magnifications up to
approximately 2000X. The sample surface is uniformly illuminated by incident light rays directed
perpendicularly to the sample surface. Light reflected back toward the objective lens is collected and
focused on the eyepieces to form the observed image.
Surfaces that are reflective and perpendicular to the light rays
appear bright. Alternatively, nonreflective or oblique features
reflect less light and appear darker.
Polarized Light - This method produces enhanced contrast
for features that have anisotropic refractive properties. Two
polarizing lenses are inserted into the optical path - one in the
incoming illumination and one between the sample and
eyepieces. When these lenses are rotated 90° to one another,
the “crossed polarizers” result in the subtraction of a portion

of the light spectrum by destructive interference. Contrast is
obtained between sample features that have different reflec-
tive properties. Many metals, including beryllium, zirconium and titanium, are anisotropic and exhibit
grain contrast with polarized light illumination. Polarized light enhances contrast for many polymer
samples and shows variations of internal stress in some clear polymers.
Interference Contrast Image of IC
Corrosion on the Inside of a Copper Pipe
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Differential Interference Contrast after Nomarski (DIC) - This method produces a 3-dimen-
sional image by creating brightness contrast on very minor topographical changes. DIC utilizes
crossed polarizers as described for polarized light. A double quartz prism is also inserted into the light
path to split the incident light into two separate paths. This results in two slightly shifted images of the
sample on the viewing plane, which produces contrast between features with different heights and
topographic orientations. The analyzer can be adjusted to obtain various degrees of interference to
enhance selected features or create contrast colors in the image.
Darkfield - Enhanced contrast from subtle topographic features is produced with this method. An
occluding disk is placed in the light path, blocking the direct vertical illumination. Peripheral rays in the
illumination are reflected in such a way that light reaches the sample at oblique angles. The absence of
incident vertical rays results in bright reflectance only from oblique features, such as ridges, pits,
scratches and particles. Thus, subtle features that might be completely invisible in bright field micros-
copy are readily observed with this method.
Quantitation - Microscope magnification is calibrated against reference standards. Lateral feature
dimensions can be measured to an accuracy greater than 0.5 µm. Computer analysis of digitally-
acquired images can measure area and volume fractions, particle sizes, grain size, and other features.
TYPICAL APPLICATIONS
• Small sample inspection
• Metal microstructure evaluation
• Small feature measurements
• Fracture mode identification

• Corrosion failure inspection
• Surface contamination evaluation
SAMPLE REQUIREMENTS
Sample size, shape, and condition requirements depend on the configuration of the microscope. Low-
magnification stereo microscopes are small and have a long focal length (up to 5 in.), so these can be
set up to examine even relatively large samples. Some portable field microscopes can be fixtured
directly to large structures. For magnifications of 100X and above, microscopes are not usually
amenable to portable use (except specialized field units). Samples for typical high-resolution light
microscopes are limited to a few pounds in weight, and examination is limited to readily accessible flat
surfaces due to the small depth of field at higher magnifications.
LIGHT MICROSCOPY
Metallurgical Light Microscope
Handbook of Analytical Methods for Materials Copyright © 2001 by Materials Evaluation and Engineering, Inc.
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METALLOGRAPHIC STUDY
DESCRIPTION OF TECHNIQUE
Metallographic study, or metallography, is the imaging of topographical or microstructural features on
prepared surfaces of materials. The structures studied by metallography are indicative of the proper-
ties and performance of materials studied.
In this technique, planar surfaces are prepared to obtain a
polished finish. Chemical or other etching methods are often
used to delineate macrostructure and microstructure features.
Once prepared, samples are examined by the unaided eye, light
microscopy, and/or electron microscopy. (See sections on Light
Microscopy and Scanning Electron Microscopy.)
Samples for microstructure evaluation are typically encapsulated
in a plastic mount for handling during sample preparation. Large
samples or samples for macrostructure evaluation can be pre-
pared without mounting. Sample preparation consists of grinding and then polishing using successively
finer abrasives to obtain the desired surface finish. For microstructure examination, a mirror finish is

needed, but a finely-ground finish is adequate for macrostructure evaluation. Etchants are specially
formulated for the specific sample material and evaluation objectives.
Sampling for metallography can be a random section to evaluate representative bulk properties or a
section in a specific location to characterize localized material conditions. For example, a section
through the facture initiation site is often made to assist with a component failure analysis. For micro-
electronic components, precision metallographic methods can obtain sections though specific wire
bonds, solder pads, or even individual components on an
integrated circuit device.
ANALYTICAL INFORMATION
Macrostructure Evaluation - Deep chemical etching is
used to characterize large-scale variations in material
composition, structure, density, etc. This method is useful
for evaluation of welds, brazes, forgings, and polymer-
matrix composites for configuration, defects, and struc-
ture.
Microstructure Evaluation - Characteristic features provide information about composition, phase
distribution, mechanical and physical properties, thermo-mechanical process history, and defects. In
failure analysis, the morphology of corrosion or cracks can be characteristic of the failure mode.
Stress Corrosion Cracking at SS Weld
Microstructure of Welded Titanium
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Quantitative Metallography - Observed features can
be analyzed to obtain measurements of microscopic
characteristics, including grain size, phase volume fractions,
and linear dimensions. Measurements are made manually
or by computerized semi-automated methods on digitally-
acquired images.
Field Metallography - Metallographic examination can
be performed in situ for large components or on structures

in the field. The selected areas of the sample surface are
polished using portable tools. The prepared surface can be
examined directly with a portable light microscope. Alter-
natively, the surface can be replicated with an acetate tape
or castable polymer for examination by light microscopy or electron microscopy in the laboratory.
TYPICAL APPLICATIONS
• Metal alloy heat treatment verification
• Coating thickness measurement
• Weld or braze joint evaluation
• Case hardening depth determination
• Corrosion resistance evaluation
• Failure analysis
• Microscopic defects in IC devices
• In situ evaluation of thermo-mechanical
degradation
SAMPLE REQUIREMENTS
Most samples are sectioned and encapsulated in a
metallographic mount to facilitate preparation. The mount
sizes range from about 1 in. (25 mm) to 3 in. (75 mm) in
diameter. Sections up to approximately 8 in. (200 mm)
across can be prepared in the laboratory without mount-
ing. Localized areas on large samples or those that
cannot be cut are prepared in situ and evaluated using a
field microscope or replicas of the prepared surface.
METALLOGRAPHIC STUDY
Manganese Bronze Microstructure
Mis-registration in Multilayered Circuit Board
Plating Defect Caused by Chemical Attack
Before Plating at Nonmetallic Inclusion
Handbook of Analytical Methods for Materials Copyright © 2001 by Materials Evaluation and Engineering, Inc.

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MICROINDENTATION HARDNESS TESTING
DESCRIPTION OF TECHNIQUE
Microindentation hardness testing (or microhardness testing) is a method for measuring the hardness
of a material on a microscopic scale. A precision
diamond indenter is impressed into the material at
loads from a few grams to 1 kilogram. The impres-
sion length, measured microscopically, and the test
load are used to calculate a hardness value. The
hardness values obtained are useful indicators of a
material’s properties and expected service behavior.
Conversions from microindentation hardness values
to tensile strength and other hardness scales (e.g.,
Rockwell) are available for many metals and alloys.
The indentations are typically made using either a square-based pyramid indenter (Vickers hardness
scale) or an elongated, rhombohedral-shaped indenter (Knoop hardness scale). The tester applies the
selected test load using dead weights. The length of the hardness impressions are precisely measured
with a light microscope using either a filar eyepiece or a video image and computer software. A
hardness number is then calculated using the test load, the impression length, and a shape factor for
the indenter type used for the test.
ANALYTICAL INFORMATION
Bulk Hardness - Randomly-located impressions measure
the representative bulk hardness value of a relatively
homogeneous material.
Localized Hardness - Impressions are made at specific
sites located using the light microscope to determine the
hardness at discrete features or phases in the sample.
Hardness can be measured for features less than 0.1 mm
across.
Hardness Survey - A series of hardness impressions are made along a line from a surface or a

specific point in the sample to systematically measure the hardness variation within a sample.
Thin Coatings - The hardness of coatings as thin as a few microns can be determined by measuring
directly on the coated surface of a sample. Coating thickness must be known to assess accuracy of
these measurements.
Knoop Microindentation Hardness Survey for
Chromium-Plated, Case-Hardened Steel
Knoop Indenter Vickers Indenter
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TYPICAL APPLICATIONS
• Bulk hardness of small or thin samples
• Heat treated steel case depth evaluation
• Decarburization in steels
• Evaluation of welds
• Hardness of thin coatings
• Evaluation of machinability
SAMPLE REQUIREMENTS
Most microindentation hardness testing is performed on samples that have been metallographically
mounted and polished. These samples are usually no larger than about 1 in. (25 mm) by 1 in. (25
mm) by 1/2 in. (12 mm) thick. Larger samples can be tested with special fixturing. Thin, flat samples,
such as sheet material, can be tested without mounting or preparation if the surface finish is suitable.
The ideal surface finish is a high-quality metallographic polish. Where polishing is not feasible, the
surface finish must be sufficiently smooth and reflective to clearly resolve the microscopic hardness
impression with the measuring microscope. The specific finish requirement depends on the material
and test load.
MICROINDENTATION HARDNESS TESTING
Microhardness Tester
Handbook of Analytical Methods for Materials Copyright © 2001 by Materials Evaluation and Engineering, Inc.
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NANOINDENTATION HARDNESS TESTING

DESCRIPTION OF TECHNIQUE
Nanoindenting is a new method to characterize material mechanical properties on a very small scale.
Features less than 100 nm across, as well as thin films less than 5 nm thick, can be evaluated. Test
methods include indentation for comparative and quantitative hardness determination and scratching
for evaluation of wear resistance and thin film adhesion.
Nanoindenting is performed in conjunction with atomic force microscopy (AFM). The area for testing
is located by AFM imaging, and indentations and scratching marks are imaged by AFM after testing.
A three-sided, pyramid-shaped diamond probe tip is
typically used to indent, scratch and image the sample.
For indentation, the probe is forced into the surface at a
selected rate and to a selected maximum force. In
scratching, the probe is dragged across the sample
surface. The force, rate, length and angle of the scratch
is controlled.
Imaging is performed in situ using the probe in intermit-
tent contact (tapping mode) AFM. The depth of the
indentation is measured from the AFM image to evaluate
hardness. A force-displacement curve obtained during indentation also provides indications of the
sample material’s mechanical and physical properties.
ANALYTICAL INFORMATION
Nanoindentation - Indentation forces ranging from 1µN to 100 mN can be made to measure
material hardness. Indentation depth or area is inversely proportional to hardness. Force displace-
ment curves obtained during the indentation process indicate hardness and elastic modulus properties.
Scratching - Patterns scribed in the sample surface show the potential for spalling or delamination of
thin films.
Wear Testing - The diamond probe tip is repeatedly scanned over the same sample surface area at
a selected force. Wear durability is measured by the material lost from the tested surface. Depth of
material loss is measured by AFM imaging after testing.
AFM Images of Two Impressions in a Polymer
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TYPICAL APPLICATIONS
• Hardness measurements for submicron-size features
• Thin film adhesion evaluation
• Coating wear durability evaluation
• Elastic modulus comparisons for thin films
SAMPLE REQUIREMENTS
Samples up to 8 in. (200 mm) across and 1 in. (25 mm) thick can be fixtured and tested in some
instruments. Larger samples can be fixtured for access to limited surface areas. The sample surface
must have a smooth finish for uniform indentation and to allow AFM imaging for indentation depth.
The required finish depends on the material and the test force.
NANOIDENTATION HARDNESS TESTING
AFM Section Analysis for Nanoindentation Hardness
Handbook of Analytical Methods for Materials Copyright © 2001 by Materials Evaluation and Engineering, Inc.
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QUANTITATIVE CHEMICAL ANALYSIS
DESCRIPTION OF TECHNIQUES
Quantitative chemical analysis is performed to accurately determine the concentration of elements in
the material comprising a given sample. A variety of analysis techniques are used for metals and alloys
to determine the alloy composition of raw materials to verify conformance to a specification or to
identify the alloy used to make a specific component. Quantitative analysis methods are also used
occasionally for evaluation of foreign material contaminants in special cases for failure analysis or
investigation of product manufacturing or handling problems.
Quantitative chemical analysis may be performed by one or more complimentary techniques, com-
monly including spark optical emission spectroscopy (Spark-OES), inductively-coupled plasma
spectroscopy optical emission spectroscopy (ICP-OES), x-ray fluorescence spectroscopy (XRF),
wet chemical analyses, combustion methods, and inert gas fusion(IG).The specific technique chosen
will depend on the type of sample, quantity of material available for analysis, desired result, and cost
constraints. In most cases, the applicable analysis techniques can detect parts-per-million concentra-
tions or better.

Most of these techniques are destructive to the original sample. XRF can be performed nondestruc-
tively and Spark-OES can be performed with only minimal surface damage if the specimen size
configuration allow the part to fit into the instrument without cutting. For the remaining methods
discussed here, a small specimen is removed from the sample and is consumed in the analysis.
Prior to the widespread availability of analytical instruments, chemical analyses were performed by
dissolving the sample and performing a specific chemical reaction with a standardized reagent for
each element of interest. These ‘wet chemistry’ techniques are typically labor intensive and time
consuming, and sometimes less accurate than the current instrumental methods.
Wet Chemistry - These methods include gravimetric and titrimetric techniques. An example of a
gravimetric technique is the precipitation of chloride ion with silver to form a silver chloride precipitate
which is dried and weighed to determine the chloride concentration in the original sample solution.
Titrimetric procedures are typically based on acid-base reactions or complexing agents for metal ions.
Since wet chemical analyses are now less common for the analysis of metals and similar inorganic
materials, the remainder of this section will focus on the instrumental methods of analysis.
Spark-OES - Spark optical emission spectroscopy is a technique used for direct analysis of solid
metal samples. The specimen is prepared by grinding to obtain a uniform, clean, flat area about 1 to 2
cm across. The prepared sample is placed in the spark-OES instrument and flooded with argon. A
rapid series of high energy sparks are created across the argon-filled gap between an electrode
(cathode) and the prepared sample’s surface (acting as the anode). The sparks first ionize the argon,
creating a conductive plasma. Secondly, the sparks melt, evaporate, and excite the sample elements
at the spark point of impact. When the excited atoms in the plasma relax (de-excite) to a lower
energy state, they emit light at characteristic wavelengths for each element. The intensities of these
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emissions at the characteristic wavelengths are detected, measured, and compared to intensities for
known standards to provide quantitative results. The total duration of the sparking is only a few
milliseconds. Prior to actual measurements, the sample surface may be subjected to high power
discharges to melt the surface and create a more homogeneous material.
XRF - X-ray fluorescence spectroscopy is a technique that can be used for direct analysis of solid
metal samples, thin metal films, petroleum products, cement, coal, and various other materials. XRF is

a fast technique and is non-destructive to the sample. It is frequently used for analyses performed in
the field and for industrial quality control.
An x-ray tube is used to irradiate the sample with a primary beam of x-rays. Some of the impinging
primary x-rays are absorbed by the sample elements in a process known as the photoelectric effect.
The photoelectric effect occurs when all the energy of a primary x-ray is absorbed by an electron in
an atom’s innermost electron shell. This causes excitation and ejection of the absorbing electron
(photoejection). The electron vacancies caused by the photoelectric effect are filled by electrons from
higher energy states, and x-rays are emitted (fluorescence) to balance the energy difference between
the electron states. The x-ray energy is characteristic of the element from which it was emitted.
The fluorescence x-rays are collimated and directed to an x-ray detector. The energy of each x-ray
and number of x-rays at each energy are recorded. The x-ray intensities (counts) at each energy are
compared to values for known standards for quantitatively analysis of the unknown specimen.
ICP-OES - Inductively coupled plasma-optical emission spectroscopy is a technique for analyzing
the concentration of metallic elements in solid and liquid samples. Like spark-OES, ICP-OES uses
the optical emission principles of exited atoms to determine the elemental concentration. However, for
ICP-OES, solid samples are dissolved (digested) in an appropriate solvent (typically acid) to pro-
duce a solution for analysis. The resulting sample solution (or an original liquid solution for analysis) is
often diluted in water to obtain a final specimen suitable for analysis.
The ICP-OES instrument uses argon gas flowing through a torch consisting of three concentric quartz
tubes. A copper coil circumscribing the top of the torch is connected to a radio frequency (RF)
generator. The use of the copper coil with the RF power is called inductive coupling.
When the RF power is applied in the copper coil, an alternating current occurs within the coil. The
oscillation of the alternating current causes electric and magnetic fields at the end of the torch. A spark
applied to the argon gas causes some electrons to be stripped from the argon atoms. The electrons
are caught and accelerated by the RF generated electric/magnetic field. The high energy free electrons
collide with other atoms, stripping off more electrons in a chain reaction, resulting in a plasma of
electrons, ions, and atoms. This is known as an inductively coupled plasma (ICP) discharge. This ICP
discharge is maintained as the RF energy is continually transferred to the plasma by the copper coil.
The liquid samples are nebulized into an aerosol and introduced into the center of the plasma. The
plasma excites the sample atoms, which subsequently relax to a lower energy state by emitting light at

elementally characteristic wavelengths. The intensities of these characteristic wavelengths are de-
tected, measured, and compared to intensities for known standards to provide quantitative results.
QUANTITATIVE CHEMICAL ANALYSIS