1. Preparation of Specimens for Metallographic Examination
Exp.#1.

2. Objective
To prepare the specimens surfaces to be examined by the microscope.
To learn and to gain experience in the preparation of metallographic specimens.
Exp.4: Preparation of Specimens
11/13/2018

3. 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.
Such microscopic studies can provide an abundance of constitutional information about the specimen under investigation, including the size and shape of the grains (crystallites), the presence of micro defects (such as segregation, hair cracks, and nonmetallic inclusions), and the nature and distribution of secondary phases.
The metallographic examination can be used in quality control and to predict and/or explain the mechanical properties.
Exp.4: Preparation of Specimens
11/13/2018

4. 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), ultrasonic cleaning, mounting, course grinding, fine grinding, and polishing, etching and microscopic examination. Specimens must be kept clean and preparation procedure carefully followed in order to reveal accurate microstructures
Exp.4: Preparation of Specimens
11/13/2018

5. Equipment
Minitom: Small, automatic precision cut-off machine for sectioning all metallographic and ceramic specimens.
Metason: Ultrasonic Cleaning: For effective ultrasonic cleaning of metallographic, ceramic, and mineralogical specimens
LaboPress-3 :Semi-automatic mounting press for hot mounting of all materials.
Exp.4: Preparation of Specimens
11/13/2018

6. Equipment cont.
LaboPol (grinding and polishing machine): Machines for grinding, lapping and polishing for 200 or 230 mm discs.
LaboForce : Specimen movers for semi-automatic preparation of materialographic specimens on LaboPol grinding and polishing machines.
LectroPol-5: Automatic, microprocessor controlled electrolytic polishing and etching of metallographic specimens
Exp.4: Preparation of Specimens
11/13/2018

7. Hot Mounting In hot-mounting the sample is surrounded by an organic polymeric powder which melts under the influence of heat (about 200 oC). Pressure is also applied by a piston, ensuring a high quality mould free of porosity and with intimate contact between the sample and the polymer.
Cylinder dia.
Resin
heating
Cooling
30 mm
Type
Quantity
Time
Temp.
Force
Rate
[spoons]
[ml]
[min]
[oC]
[kN]
PolyFast
1.5 23
4-6
180 20
2-3
HIGH
MultiFast (block) 2 30
Exp.4: Preparation of Specimens
11/13/2018

8. Optimizing the amount of resin
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 =
The factor 1.2 is multiplied to eliminate variation in the resin densities and the measuring during mounting.
Height of 1 Spoon (15 ml) of Resin after Mounting in an Empty Cylinder
Cylinder dia:
30 mm
Resin: mm
inch
PolyFast
11.3
0.44
MultiFast (black)
8.9
0.35
Exp.4: Preparation of Specimens
11/13/2018

9. Grinding and Polishing The specimen must: 1
Grinding and Polishing The specimen must: 1. Be free from scratches, stains and others imperfections which tend to mark the surface. 2. Retain non-metallic inclusions. 3. Reveal no evidence of chipping due to brittle intermetallic compounds and phases. 4. Be free from all traces of disturbed metal.
Indication
Force (N) 1
2.2 2 5 3
7.5 4 10
12.5 6 15 7
17.5 8 20
Exp.4: Preparation of Specimens
11/13/2018

10. Grinding Surface MD-Primo 220 MD-Largo Abrasive SiC DP-Suspension
Grit / Grain size -
9µm
Lubricant
Water
Green/Blue
rpm
300
150
Force(N)
120
180
Time (min)
Until Plane 5
Exp.4: Preparation of Specimens
11/13/2018

11. Polishing Surface Abrasive Grit / Grain size Lubricant rpm Force(N)
MD-Dac
MD-Nap or MD-Chem
Abrasive
DP-Suspension
OP-S or OP-U
Grit / Grain size
3µm -
Lubricant
Green/Blue
rpm
150
Force(N)
190 60
Time (min) 5
Exp.4: Preparation of Specimens
11/13/2018

12. Electrolytic Polishing
Exp.4: Preparation of Specimens
11/13/2018

13. Electrolytes: Sample material Etchant Composition Remarks Carbon steel
(usually 2%)
(nitric acid)
HNO ml
Ethyl alcohol 100ml
Immersion. Time ranges from a few seconds to a minute
(picric acid)
Picric acid g
Immersion. Time ranges from a few seconds to
Over a minute.
Aluminum
Hydrofluoric acid
HF (concen) ml
H2O ml
Swab for 15 sec.
Copper-based alloys
50% nitric acid
50% distilled water
Exp.4: Preparation of Specimens
11/13/2018

14. Questions
Describe the steps involved in the preparation of a metallographic sample:
Sectioning (cutting)
Plastic coating of the samples
Mounting
Grinding
Polishing
Etching
Why should the specimen be roughly washed after each stage during either grinding or polishing?
Why is fine grinding performed wet?
What is the purpose of etching metallographic samples?
What are the advantages of electrolytic polishing?
Exp.4: Preparation of Specimens
11/13/2018