1. Group members : 19M2052 Sarika
19M2050 Riya
19M2051 Sajal jain
19M2053 Sachi shrivastava
19M2054 Shail kumari verma
19M2055 Shubhanshu kushwaha
19M2056 Simran sardar
2. 1. To learn and to
gain experience in
the preparation of
metallographic
specimens.
2. To examine and
analyze the
microstructures of
metals and metallic
alloys.
3. WHAT IS
METALLOGR
APHY??
Metallography basically is
the study of the
structures and
constitutution of metals
and alloys using
metallurgical
microscopes and
magnifications, so that
the physical and
mechanical properties of
an alloy can be related to
its obtained
microstructure.
4. Metallography is the science and art of preparing a metal
surface for analysis by grinding, polishing, and etching to
show microstructual component.
5. • Metallurgical microscope is the most important
tool for the metallurgist for observing a
microstructure and studying various Metals or
alloys and their uses in engineering applications.
• In contrast to biological microscopes,
this microscope uses the principal of reflection
of light, which will be due to polished
or opaque specimen-surface.
Types of metallurgical microscopes:
1.optical microscope
2.Scanning electron microscope
3.Transmission electron microscope
4.Auger electron microscope
6.
7. Sample preparation is the process of
preparing the metallographic specimen to
determine microstructure or for metallurgic
analysis.
For this there are 6 step by step processes
involved that should be followed in sequence.
These steps are
1.Cutting 2.Mounting 3.Granding
4.Polishing 5.Etching 6.Observing.
9. Sectioning is the first step
in the overall
process of specimen
preparation. It is a step
that should be given
considerable thought and
care. Where the
sectioning should be
placed, and also the
proper equipment to use
should be considered.
10. MOUNTING
Small samples can be difficult
to hold safely during grinding
and polishing operations, and
their shape may not be
suitable for observation on a
flat surface. Therefore Small
samples are generally
mounted in plastic for
convenience in handling and
to protect the edges of the
specimen being prepared.
11. Cold mounting in a vacuum is required for green
specimens and samples taken from magnetic
applications. All pores connected to the surface
require special procedures that include the use of
epoxy resin and vacuum impregnation. The
specimens are put in a cup and air is evacuated in a
vacuum chamber for at least 15 minutes. When
evacuation is completed, resin is carefully poured
over the specimens. The specimens are then cured
at 70°C for 1-2 hours.
12. Cold mounting can be done using two components
resins (epoxies) which are liquid to start with but
which set solid shortly after mixing.
It requires very simple equipment consisting of a
cylindrical ring which serves as a mould and a
flat piece which serves as the base of the mould.
the sample is placed on the flat piece within the
mould and the mixture poured in and allowed to
set. Cold mounting takes few hours to complete.
13. Hot compression mounting is used with
sintered and heat-treated specimens. The
sample is put in the mounting press and
1/3 of resin with glass fibre is added first
and then 2/3 of bakelite. The sample is
processed under high pressure both
during the heating and cooling cycles.
This results in the least shrinkage and
helps to maintain good adhesion between
the resin and the sample.
14. Hot compression mounting can also be
used with metallic powders. It is
possible to reach a good result with
hot mounting of powder particles if a
resin with fine particle size is used.
Mix 1-2 ml of the powder with 5 ml of a
fineparticle resin in a small container.
Pour the powder mix in the mounting
press, add 5 ml bakelite on top, and
process as above.
15. GRINDING
grinding removes
damaged or deformed
surface material, while
introducing only limited
amounts of new
deformation. The aim is
to reach a plane surface
while creating minimal
damage that can be
removed easily during
polishing, in the shortest
possible time. Grinding
consists of two separate
processes: Plane
grinding and
16. Plane grinding :- Plane grinding ensures that the surface of all
specimens are similar and in the same level or plane. Relatively
coarse fixed abrasive particles are used to remove material
quickly. SiC papers or Al2 O3 grinding stones are employed
with most ferrous materials.
Fine grinding:- Fine grinding produces a surface with such a
small amount of deformation that it can be removed during
polishing. Five different grades of SiC paper (220, 320, 500, 800
and 1200 mesh) or a thin hard composite disc with 9 µm DP-
suspension can be used for fine grinding. For non-sintered
components and powders, it is usually possible to begin fine
grinding with SiC paper 500 or 800.
19. After the final grinding operation on 1200 paper,
wash the sample in water followed by alcohol and
dry it before moving to the polishers.
Polishing
After grinding, the pores on a sample surface will
be almost completely smeared. The aim of
polishing is to open all the pores, and to show the
true area-fraction of porosity, and to remove
scratches.
20. The polishers consist of rotating discs covered with soft
cloth impregnated with a pre-prepared slurry of hard
powdery alumina particles (Al2O3, the size ranges
from 0.5 to 0.03 µm).
Begin with the coarse slurry and continue
polishing until the grinding scratches have been
removed. It is of vital importance that the
sample is thoroughly cleaned using soapy water,
followed by alcohol, and dried before moving onto
the final stage. Any contamination of the final
polishing disc will make it impossible to achieve
a satisfactory polish.
Examining the specimen in the microscope after
polishing should reveal mirror like surface.
21. ETCHING
The purpose of etching is two-fold.
1. Grinding and polishing operations produce a
highly deformed, thin layer on the surface which
is removed chemically during etching.
2. attacks the surface with preference for those
sites with the highest energy, leading to surface
relief which allows different crystal
orientations, grain boundaries, precipitates,
phases and defects to be distinguished in
reflected light microscopy .
22. Etching should always be done in stages,
beginning with light attack, an examination in
the microscope and further etching only if
required.
If you overetch a sample on the first step then
the polishing procedure will have to be repeated.
The table below gives the etchants for alloys that will
be examined in this experiment
.Kellers (2 ml HF 3 ml HCL 5 ml NO3 190 ml water)
Al alloys
10 ml HNO390 ml water Cu-Zn alloy (brass)
Nital (2 HNO3 98 ethanol) Steel and cast irons
23.
24. 1 .Nital Fe 1 100 ml - 95% Ethyl alcohol, 1 ml
concentrated HNO3 .
Etching time: 10-60 seconds
Common etchant for steel with ferritic, pearlitic and
bainitic structures. Base materials: NC100.24,
SC100.26, ASC100.29, AHC100.29, PASC and PNC-
grades, Astaloy™ A, Astaloy Mo and Astaloy 85 Mo.
Uses: • Grain boundaries in ferrite. • Amount of
pearlite and ferrite to estimate carbon content. •
Amount of martensite to define the case depth. • 4%
Nital can be used to detect the diffusion of
phosphorous in PASC and PNC materials.
25. 2. Picral ( 100 ml-95% Ethyl alcohol, 4 g
Picric acid).
Etching time: 10-60 seconds
depending on carbon content. Etchant for
materials where Ni is diffusion bonded or
added in the mix.
Uses: For diffusion bonded Ni or mixed in Ni.
26. 3. Nital + Picral (100 ml 95% Ethyl alcohol, 4g
Picric acid +1-2 ml HNO3).
Etching time: 20-100 seconds depending on
carbon and alloying content. Martensitic
structures need longer times and sometimes it is
necessary to add 2 ml HNO3 to the etchant. It is
an etchant for pre-alloyed materials with low Cr-
content.
Uses: To develop good contrast between pearlite,
bainite, martensite and lower bainite.
27. In observing we obserb the grains developed .
Initial microscopic viewing should be done utilizing a
stereomicroscope, which reveals a three-dimensional
scanning of the specimen surface. The specimen is
placed on the stage of the microscope so that its
surface is perpendicular to the optical axis. Detailed
viewing is done with a Metallurgical Microscope.
A metallurgical microscope has a system of lenses
(objectives and eyepiece) so that different
magnifications (25X to 1000X) can be achieved.
28. . The important characteristics of the microscope are:
(1) magnification, (2) resolution and (3) flatness of field.
The resultant magnification is the product of the
magnifying power of the objective and that of the ocular.
Scanning Electron Microscopes (SEMs) are capable of
magnifications up to 20,000X and Transmission Electron
Microscopes (TEMs) are utilized to view at magnifications
up to 100,000X for highly detailed microstructural study.
The ASTM grain size number, n, can be calculated
using the following relationship:
N (M/100)2 = 2(n - 1)
N = number of grains per square inch at 100X n =
ASTM grain size number
M = Magnification
