04/18/231Exp.4: Preparation of Specimens

To prepare the specimens surfaces to be examined by the microscope.

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

04/18/23 2Exp.4: Preparation of Specimens

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.

04/18/23 3Exp.4: Preparation of Specimens

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, 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

04/18/23 4Exp.4: Preparation of Specimens

Minitom: Small, automatic precision cut-off machine for sectioning all materialographic 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.

04/18/23 5Exp.4: Preparation of Specimens

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

04/18/23 6Exp.4: Preparation of Specimens

04/18/23 7Exp.4: Preparation of Specimens

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 mm) of Resin after Mounting in an Empty Cylinder

1.2

sin

hight sample

height of one spoon of re

04/18/23 8Exp.4: Preparation of Specimens

04/18/23 9Exp.4: Preparation of Specimens

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 504/18/23 10Exp.4: Preparation of Specimens

Surface MD-Dac MD-Nap or MD-Chem

Abrasive DP-Suspension OP-S or OP-U

Grit / Grain size 3µm -

Lubricant Green/Blue -

rpm 150 150

Force(N) 190 60

Time (min) 5

04/18/23 11Exp.4: Preparation of Specimens

04/18/23 12Exp.4: Preparation of Specimens

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? 

04/18/23 13Exp.4: Preparation of Specimens