Exp.3: Preparation of Specimens for

Metallographic Examination

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ENG. MOHAMMED ABU ELKHAER

ENG.HASAN ZAIDAH

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Objective of the experiment

To learn and to gain experience in the preparation of metallographic specimens.

To prepare the specimens surfaces to be examined for their microstructure study by the

microscope .

Introduction

Metallography is basically the study of the structures and

constitution of metals and alloys, using metallurgical microscopes

and magnifications, so that the physical and mechanical properties

of an alloy can be related to its observed microstructure.

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Introduction …cont.

Such microscopic studies can provide constitutional information

about the specimen under investigation, including:

• The size and shape of the grains,

• The presence of micro defects.

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Introduction …cont.

Proper preparation of metallographic specimens to determine

microstructure and content requires that a rigid step-by-step

process be followed. In sequence, the steps include:

• Sectioning (cutting),

• Mounting,

• Grinding,

• Polishing,

• Etching ,

• Microscopic examination.October 11,

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Sectioning (cutting)

The preparation starts by cutting a small representative piece of the

metal to be studied.

Cutting can change the microstructure of a sample.

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Sectioning (cutting)

Minitom: Small, automatic precision cut-off machine for

sectioning all materialographic and ceramic specimens.

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Cleaning

Specimens must be kept clean in order to reveal accurate

microstructures.

Metason: Ultrasonic Cleaning.

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Cleaning

The process is carried out using an ultrasonic cleaning machine.

The process removes dirties and loose particles.

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Mounting

The process of coating the sample.

Mounting of specimens is usually necessary to:

• Allow them to be handled easily.

• Minimizes the amount of damage likely to be caused to the

specimen itself.

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Mounting

LaboPress-3: Semi-automatic mounting press for hot mounting of all

materials.

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Mounting

In hot-mounting the sample is surrounded by an organic polymeric

powder which melts under the influence of heat (about 200 𝑂𝐶).

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Mounting

It is important to supply enough resin during mounting. If the

amount of resin is too small to cover the specimen after curing, the

specimen, the ram and the cylinder may all be damaged.

Min. no. of Spoons =

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Grinding

Surface layers damaged by cutting must be removed by grinding.

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Grinding

LaboPol (grinding and polishing machine): Machines for

grinding, lapping and polishing for 200 or 230 mm discs.

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MD-Largo MD-Primo

Grinding

LaboForce: Specimen movers for semi-automatic

preparation of materialographic specimens on LaboPol

grinding and polishing machines.

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Grinding

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Polishing

To remove deformations from grinding and obtain a surface that is

highly reflective.

Polishing discs are covered with soft cloth.

MD-ClothsOctober 11,

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Polishing

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Etching

Etching occurs when the acid or base is placed on the specimen

surface. The purpose of etching:

• Grinding and polishing operations produce a highly deformed,

thin layer on the surface which is removed chemically during

etching.

• Etching is used to reveal the microstructure of the metal

through selective chemical attack.October 11,

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Etching

LectroPol-5: Automatic, microprocessor controlled

electrolytic polishing and etching of metallographic

specimens.

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Grinding

Polishing Etching

More Etching

Procedure

n100 = Nm * [M / 100]2

n100 : number of grains per square inch at 100x magnification.

Nm : number of grains per square inch at the magnification M of the

photomicrograph.

N100= 2N-1

The ASTM grain size number N= [ ln (N100 ) / ln ( 2) ] + 1

How to calculate the are of one grain (actual area of grain at M1)?

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How to calculate the grain size

Let M =200

A = 2*3 = 6 inch2

nm = 200 grain /6 inch2 = 33.3 grain / inch2

n100 = nm * [M / 100]2

=33.3*[200/100]2

n100 =133.2 grain / inch2

N= [ ln ( n ) / ln ( 2) ] + 1

= [ ln ( 133.2) / ln ( 2) ] + 1

= 8.06 grain / inch2

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