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Contents Page no.

1. Abstract …………………………………..(2)

2. Metallography Introduction ……………...( 3)

3. Quantitative Metallography Introduction…(4)

4. Quantitative Metallography Applications...(7)

5. Quantitative Metallography Methods …….(8)

Comparison Method …………………………….(8)

Measurement Method…………………………..(9)

6. Quantitative Metallography Equipments ...(18)

7. Summary………………………………….(19)

8. References ………………………………..(21)

9. External Links…………………………….(22)

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Abstract WHEN MAKING A QUALITATIVE EXAMINATION OF A

MICROSTRUCTURE, the interpretation of the structure is to a high

degree based on the knowledge and experience of the observer. In

quantitative metallography/materialography the constituents in the

microstructure are measured to provide more reliable data for

materials engineering and quality control purposes. Typical

microstructural measurements include the length, width, and area of

features or the relative amount of a structure or phase. The

application of stereological principles enables two-dimensional

measurement data extracted from metallographic/materialographic

specimens to provide accurate information about three-dimensional

structures increasing the usefulness and importance of quantitative

microstructural analysis. It can be tedious to implement quantitative

methods. Digital image analysis equipment and software have been

developed as tools to automate the collection and reporting of

quantitative data.

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Metallography

Metallography is the study of the physical structure and

components of metals, typically using microscopy.

Ceramic and polymeric materials may also be prepared

using metallographic techniques, hence the

terms ceramography, plastography and, collectively,

materialography.

A micrograph of bronze revealing a cast dendritic

structure

In some cases, the metallographic structure is

Larg enough to be seen with the unaided eye.

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Quantitative metallography

Quantitative Metallography involves determination of specific

characteristics of a microstructure by making quantitative

measurements on micrographs or metallographic images.Quantities

so measured include volume concentration of phases, grain size,

particle size and surface area to volume ratio of micro constituents.

A number of techniques exist to quantitatively analyze

metallographic specimens. These techniques are valuable in the

research and production of all metals and alloys and non-metallic

or composite materials.

Microstructural quantification is performed on a prepared, two-

dimensional plane through the three-dimensional part or component.

Measurements may involve simple metrology techniques, e.g., the

measurement of the thickness of a surface coating, or the apparent

diameter of a discrete second-phase particle, (for

example, spheroidal graphite in ductile iron). Measurement may also

require application of stereology to assess matrix and second-phase

structures. Stereology is the field of taking 0-, 1- or 2-dimensional

measurements on the two-dimensional sectioning plane and

estimating the amount, size, shape or distribution of the

microstructure in three dimensions. These measurements may be

made using manual procedures with the aid of templates overlaying

the microstructure, or with automated image analyzers. In all cases,

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adequate sampling must be made to obtain a proper statistical basis

for the measurement. Efforts to eliminate bias are required.

An image of the microstructures of ductile cast iron.

Some of the most basic measurements include determination of

the volume fraction of a phase or constituent, measurement of

the grain size in polycrystalline metals and alloys, measurement of

the size and size distribution of particles, assessment of the shape of

particles, and spacing between particles.

Standards organizations, including ASTM International's Committee

E-4 on Metallography and some other national and international

organizations, have developed standard test methods describing how

to characterize microstructures quantitatively.

For example, the amount of a phase or constituent, that is, its volume

fraction, is defined in ASTM E 562; manual grain size measurements

are described in ASTM E 112 (equiaxed grain structures with a

single size distribution) and E 1182 (specimens with a bi-modal grain

size distribution); while ASTM E 1382 describes how any grain size

type or condition can be measured using image analysis methods.

Characterization of nonmetallic inclusions using standard charts is

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described in ASTM E 45 (historically, E 45 covered only manual

chart methods and an image analysis method for making such chart

measurements was described in ASTM E 1122. The image analysis

methods are currently being incorporated into E 45). A stereological

method for characterizing discrete second-phase particles, such as

nonmetallic inclusions, carbides, graphite, etc., is presented in ASTM

E 1245.

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Quantitative Metallography Applications :-

Grain size measurement

Inclusion rating

Determination of porosity in sintered carbides

Classification of graphite structure in Cast irons.

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QUANTITATIVE METALLOGRAPHY Methods:

There are two methods used in quantitative metallography

1)- Comparison method

2)- Measurement method

Comparison Method

It is a quickest method for routine analysis

In this method, the microstructure image or micrograph is compared

with series of Standard charts. In Microscopes, facilities are provided

for inserting standard templates which are reproduced simultaneously

with the object, thus making for easy and rapid comparison. The

standard charts and templates have been issued by ASTM, ISO & SIS

for,

• Grain size measurement

• Inclusion rating

• Determination of porosity in sintered carbides

• Classification of graphite structure in Cast irons.

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Measurement Methods

# Microscopic measurements can be made either,

• On the virtual image in the microscope

• On the micrograph

• On the ground glass screen

# Advanced microscope with image analyzing facilities give fully

automatic quantitative measurements.

# The measuring methods are,

• By comparison with charts or templates

• By means of square grid

- Measuring ways are,

Measuring the area of each individual particle or grain.

Then measured areas are divided by the square of the

linear magnification.

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Drawing straight lines on the image projected on the

ground glass screen or micrograph .The average grain size

is the total length of the lines divided by number of grains

intercepts and by the linear magnification.

- Determination of Particle size and Number

-Comparison method

When determining particle size and size distribution

of powders, inclusion etc., the area, diameter or

length of each individual particle is measured

The standard reference template is placed over the

image projected on the microscope ground glass

screen or micrograph.

Each particle is then classified in accordance with

such templates.

- Determination of Particle size and Number

Comparison method, Graphite Shape comparison as per ASTM A247

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- Determination of Particle size and Number

- Linear analysis

• Drawing straight lines on the image or micrograph ,the length of all

intercepts for a certain phase are summated.

• The Ratio between the summated length and the total length of the

lines is equal to the volume fraction which occupies the structure.

- Point counting method (ASTM E 562)

• A standard grid containing large number of points is placed on

the image or micrograph

.• The number of points which coincide with the phase ,in

comparison with the total number of grid points gives the

surface proportion (or volume fraction) of the phase.

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• For accuracy, large number of grid points must be used.

Determination of Particle size and Number

Point counting method (ASTM E 562)

• The grid consists of 100 points

• 7 “points” were inside the constituent of interest. So, the point fraction is

calculated as:

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_ Determination of Grain size :

Comparison method

It is the simplest method in determining grain size

For spherical, equiaxed grains standard charts are available

from ASTM (ASTM E 112)

For Elongated grains reference charts also available ,but usually

other methods like Planimetric and intercepts methods are used

A round , polished and etched specimen surface is compared

with standard charts and templates.

Comparison method ASTM E112 Plate II ,Rating of Grain size of

Austenitic Twinned alloy

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Comparison method ASTM E112 Plate III, Rating of Austenitic Grain

size of copper alloy

- Planimetric method (Jeffries method)

In this method a Circle or rectangle of known area is drawn on

the image on the ground glass screen or micrograph.

A magnification should be selected such that at least 50 grains

are thus enclosed

In counting, half the number of grains which are cut the

confining lines is added to number of grains inside the area

The average grain area=Total surface area / ( No .of grains x

surface magnification (M2) )

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The Root of this value is designated as the average grain size.

For elongated grains, determination should be made in three

section surfaces which right angles to each other. The number of

grains per cubic millimeter is N = 0.7 (n1 x n2 x n3) ^ ½ where,

n1, n2, n3 are three planes of intersection

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- Determination of Grain size

- Planimetric method (Jeffries method)

n1= number of grains completely inside the test circle

n2= number of grains intercepting the circle

f = Jeffries multiplier; f = magnification^ 2/circle area

Magnification 100X

NA = Average Grain area

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- Determination of Grain size

- Intercept method

• It is simple and rapid than Planimetric method

.• In this method, the number of grains which are cut by straight

lines are measured

.• The total length of the straight line is divided by the No. of

grains cut by the lines and by the linear magnification.

• The total length of the straight line drawn should cut at least

50 grains.

• In elongated grains, measurement is carried out in three

directions at right angles & one is parallel to elongated

direction. The Number of grains/Cmm is N = 0.7 (n1xn2xn3)

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Quantitative Metallography Equipments :

1- Stereomicroscope Nikon SMZ-2T

with fibre optic illumination and digital photography (Nikon Coolpix 4500)

2- Optical Microscope ZEISS - Axioplan 2, with digital photography ZEISS

AxioCam ICc3

3- Quantitative Image Analysis PAQI

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Summary

The metallographic examination constitutes simply a planar section

view of a three dimensional structure. It is not enough to recognize

this fact; one must also understand how shape in a three dimensional

construction can degenerate into traces in random planar section. In

fact, one must be able by mental visual skill to recreate from slices of

hard boiled egg, the oblate ellipsoid when they came. For example,

an inclusion, or porosity can appear to be different when observed in

different planer section and the assessment of volume will be

qualitative and only quantitative to the extent of visual judgement.

Actual quantitative evaluation of inclusion and porosity, their shape

and size distribution are very important for predicting the mechanical

properties of the metals and alloys. Similarly, the grain size is

another important factor in the hardenability of steels, ductility of

brass and in the ductile-brittle transition of alloys. The amount of

ferrite in stainless steels is a factor in their foregeability. The average

flake size of graphite is a control parameter in the strength of gray

cast iron. These are only a few instances where numerical limits to

metallographic parameters are practical factors in quality or

production control. Since we can not obtain large number of

specimens to get correct three dimensional picture, quantitative

analysis is an appropriate alternative. Two factors must be assumed

in all such quantitative studies. The planar section or sections be

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representative of the whole. In the matter of arriving at average

values for dimensions of distributed particles one must have a

knowledge of the actual or approximate shape of the particles. Few

particles are actually perfectly spherical. but this is a mathematical

convenience.

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References

Metallurgical Microscopy by Helfrid Modin &Sten modin

Standards for Metallography by George F.Vander Voort,

Director, Research &Technology Buehler Ltd.

"Metallographic and Materialographic Specimen Preparation,

Light Microscopy, Image Analysis and Hardness Testing",

Kay Geels in collaboration with Struers A/S, ASTM

International 2006.

Metallography and Microstructures, Vol. 9, ASM Handbook,

ASM International, Materials Park, OH, 2005.

Metallography: Principles and Practice, G.F. Vander Voort,

ASM International, Materials Park, OH, 1999.

Vol. 03.01 of the ASTM Standards covers standards devoted to

metallography (and mechanical property testing)

G. Petzow, Metallographic Etching, 2nd Ed., ASM

International, 1999.

Metalog Guide, L. Bjerregaard, K. Geels, B. Ottesen, M.

Rückert, Struers A/S, Copenhagen, Denmark, 2000.

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External links

HKDH Bhadeshia An Introduction to Sample Preparation for

Metallography, Cambridge University.

Video on metallography Metallography Part I - Macroscopic

Techniques, Karlsruhe University of Applied Sciences.