Experiment 3

U13ME036 U13ME037 U13ME039

Prepared by-

Faculty –S. N. PANDYA

Preparation of Specimenfor

Microscopic Observation

Required Things:

• Piece of metal (about 30mm length and 18mm dia)

• Bench Grinder

• Belt grinder

• Emery paper or emery disk different grades(1/0,2/0,3/0,4/0)

• A piece of velvet cloth

• Chemical agent

• Drier

Purpose:

• To find out the various phases present in the material.

• To find out Approximate strength, and Hardness.

• To find out Approximate composition material.

• To find out the reason of failure of Material.

PROCEDURE:

Basically preparation of specimen for optical microscopy is done by respective processes.

Cutting required part of metal for specimen.Mounting the specimen in mounting press.Grinding the specimen as per to requirements.Polishing the specimen.Etching .

•Cut a piece from the material supplied using Proper Equipments.

• Mount the Specimen.

• This types of machines are used to mount the specimen.

Mounting press

• Grind the two opposite faces to flat surface on the bench grinder till they become parallel to each other.

Double disk polishing machine

• Choose one of the two surface and further grind it till all scratches are reduced by turning the specimen by 90 degrees before grinding on the finner grinding wheel.

Specimen

Rotating water Lubricated disk

• After removing the scratches with the help of bench grinder then the specimen through 90 degree and again grind it on belt grinder to remove scratches formed by the wheel of the bench grinder and make surface completely flat.

Bench grinder

Belt grinder

Turn the specimen through 90 degrees and using emery paper go on publishing. The specimen consequently with 1/0,2/0,3/0,4/0 papers each time turning the specimen through 90 degrees while switching over to next emery paper.

Emery paper

The same process can also be done ; if required by using Metallographic Composite Disks or using more than one Metallographic Composite Diskswe can use it as LAPPING FILMS also.

Metallographic Composite Disks

LAPPING FILMS

Etching

Apply the chemical agent (etching agent) method of etching,

oSpecimen is dipped in etching agent which is immersion method.oRubbing cotton soaked in etching agent.oElectrolyte etching.

Some general purpose Etching Agents:

• Steel and Cast iron:

(a)con. Nitric acid 2 c.c, absolute methyl alcohol 98 c.c.

(b)saturated solution of picric acid in alcohol.

• Cementite:

Picric acid 2 gm,Caustic soda 20 gm , Water 73 gm.

• Carbide in chromium steel:

Potassium ferocyanide 10 gm , kolt 10gm ,water 100 c.c.

IMMERSION:

• Specimen is immersed in the etching agent . Swabbing agent is applied with the help of a piece of cloth . This specimen is then washed in distilled water . A drop of spirit is placed on the surface and is dried with the help of the drier and then the specimen is ready to see under the metallurgical microscope.

General purpose of Etching Agent:• Material Etching agent Solvant of Etching agent Etching time

• Wrought iron 5% solution of HNO3 alcohol 30 sec. to 1 min.

• Anneled carbon and C.I. 2% solution of HNO3Or5% picric acid

alcohol 10 to 30 sec.

• Hardened and tempered high carbon steel

1% sol. Of HNO3 alcohol 5 to 15 sec.

• Low alloy steel 10% sol. Or HNO3 alcohol Up to 1 min

• Stainless steel 10% sol. Of HCl alcohol 5 to 40 min.

• High speed steel 10 gms of of potassium ferrialdehydeand 10 gms of KOH

10 c.c. of water 20 sec. to 6 min.

• Cu and its alloys 10% sol. Of ammonium sulphate water

• Magnesium alloys 2 to 4% solution of HNO3 alcohol

• Alluminium and its alloys 2% HE and HNO3 in water water

Specimen is washed with distilled water then put a drop of spirit to dry it quickly. Air is blown first cold and then hot and then again cold with the help of dryers.

After that specimen is ready which can be seen under the microscope.

Image of a low alloy steel specimen etched in 10% HNO3 in

alcohol at Different magnification.

10X5X

U13ME036 U13ME037U13ME039

SANKET RATANKARPARTH RANAARCH DESAI