MFET 3451
EXPERIMENT # 3
METALLOGRAPHY LABORATORY
OBJECTIVE: To learn specimen preparation techniques in metallography and study the microstructures of
typical engineering alloy(s).
EQUIPMENT USED:
Grinders, polishing wheels, drying fans, and metallurgical microscopes.
SUPPLIES:
Acrylic resin etching solutions (nitric acid, alcohol), Al2O3 (5µm, 1µm
and 0.05 µm) and consumable supplies as needed and given
engineering alloy specimens.
REFERENCE MATERIAL: Operating instruction of the equipment to be used.
METALLOGRAPHIC STUDY: Using steel ,aluminum and/or brass (60% Cu; 40% Zn) specimen,
and the metallurgical microscope, analyze the microstructure of your given engineering alloys.
Identify the phase or phases present and the grain size of the material
from your metallographic examination. Study the microstructures
using the metallurgical microscope and appropriate phase diagrams.
Provide interpretation of your microstructures and prepare a laboratory
report of your experiment.
PROCEDURE:
See attached experimental procedure.
ASSIGNMENT:
Each student is to prepare metallographic specimens as provided in the
laboratory, and to sketch and show typical, representative
microstructure of these specimens.
Draw the microstructure you observe in your specimens. Comment on
the phases, composition of the phase(s), amounts of phase(s), and
estimate the ASTM grain size of the microstructures.
Using phase diagram information, identify in your results the phases, amounts of phases and types of
microstructures that you observe in your metallographic analysis.
1.
From your understanding of grain size, calculate or give an
estimate if the material is coarse grained or fine grained, with
its approximate ASTM grain size number.
2.
Comment on type of deformation or heat treatment the
specimen might have undergone.
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Metallography Observation Record
Grind, polish, and etch the two specimens given to you. Draw the microstructures you observe in
your specimens.
Magnification:
Specimen:
Etchant:
Observation:
Magnification:
Specimen:
Etchant:
Observation:
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Stage I: MAKING SPECIMEN MOUNTS:
Cold mounting procedure will be used to mount the specimens. Place the sample in a
mounting cup with the help of mounting clips and then pour a mixture of resin mixture of two
components). Now allow the resin to solidify (curing) and then take the sample out of the
mounting cup. Applying release agent to the walls of the mounting cup before pouring the
resin will help in easily removing the sample after curing process.
Figure 1: Various resins used for cold
mounting
Stage II: Grinding
The specimens will be taken and grinded on different emery papers (SiC) using grinding
machine (Figure 2).
Procedure:
(1)
Open water line located behind grinder.
Starting on the 120 and then 240 grit size, place prepared specimen, or metal face down of abrasive
surface, and being sliding specimen against abrasive in a forward and backward motion.
(2)
Next, turn specimen 90 degrees and repeat above procedure on the 320 Grit surface.
(3)
Again turn specimen 90 degrees and repeat procedure (2) now on the 400 Grit surface.
(4)
Finally, turning specimen 90 degrees and repeat procedure (2) now on the 600 Grit
surface.
(5)
Close water line.
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Figure 2: Grinding Machine
Stage III: Polishing Wheels
Polish the specimen on polishing wheels (Figure 3) using liquid suspension of Al2O3 and
water, which is a very fine abrasive, until a mirror like finish is obtained. Start with 5 µm and
then with 1 µm and then proceed to 0.05 µm grit size Al2O3 powder polishing station. At this
stage the microscopic examination may reveal cracks, seams, non-metallic inclusions, and
any other similar scale inhomogeneties.
Figure 3: Polishing Station
Stage IV: Etching the Surface
Etching is the selective attack by a chemical reagent that reveals the microstructural detail of
the polished mount. The grain boundaries are attacked to a higher extent than grains because
of their high energy. This results in depression of grain boundaries. To reveal the crystalline
structure of the specimen, the polished surface is etched using appropriate etching solution.
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For this experiment use 3% Nitol (97%Alcohol-3% Nitric Acid) to etch the surface of the
polished steel specimen. For brass specimens 50% nitric acid solution can be used. The
etching solution may be applied on the specimen using a swab. It is very important to not over
etch or under etch the specimen.
Stage V: Microscopy
The etched specimen will be examined using metallurgical microscope (shown in Figure 4).
The photographs will be printed and also the digital image of the grain structure will be saved
for further image analysis.
Figure 4: Metallurgical Microscopes
References:
1. ASM Handbook, Metalography, vol. 9, ASM-International, Ohio.
2. William D. Callister Jr., “Fundamentals of Materials Science and Engineering-An Integrated
Approach”, 2nd edition, 2005, ISBN 0-471-47014-7
3. “Metallurgy and metallography of pure metals”, Edited by V.S. Yemelýanov [and] A.I.
Yevstyukhin, 1962, OCLC # 1629772.
4. Thompson Henry, “Microscopical techniques in metallurgy”, 1954, OCLC# 2144627.
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