Etching In Metallography

Preparing Electrolyte

Each specimen may require different types of electrolytes. Proper electrolyte should be selected for specimen. Please see below table for common electrolytes. Fill electrolyte container of ELOPREP with correct electrolyte and place it on polishing unit. If you have different specimens which required different electrolytes, you can use additional electrolyte containers. Thus, you do not have to change electrolyte for different types of specimen, you only need to change electrolyte container.

Choosing Masks

Acid resistant masks are used for determining polishing area of specimen. There are specific aperture on the masks. Electrolyte will contact the specimen surface from this aperture thus only this area will be polished. Masks are available with 0.5-1-2 and 5 cm2 aperture size. Mask should be placed on cathode and specimen should be placed on the mask.

Adjusting Flowrate

Flowrate of electrolyte should be adjusted before operation. In other words, electrolyte should be reached upper level of the mask without any turbulance. Otherwise, polishing operation cannot be done properly. To adjust flowrate, press Pump button without placing sample. If the flow rate is not enough, increase the set value until the flow is sufficient.

Preparing Specimen

Surface of specimen should not be rough for electrolyic preparation. Specimen should be grinded before electrolytic preparation.

Determining Correct Voltage

Voltage is one of the most important parameter for electrolytic polishing. The ELOPREP has a scanning function for easy and exact determination of the parameters. If you do not know the polishing voltage to be set for your sample, you can use the scanning function to determine the exact voltage.

• Place specimen on the mask. Be sure that the aperture is covered and closed completely.
• Place the anode arm on the top of the sample to ensure good contact.
• Enter Scan menu, set scanning voltage and flowrate parameters and press Start.
• After a while, the ideal polishing voltage for your specimen will be seen on the screen.

Electrolytic Polishing & Metallographic Etching

ELOPREP has 4 different operation modes; only polishing, only etching, automatic etching after polishing and external etching.

• Place specimen on the mask. Be sure that the aperture is covered and closed completely.
• Place the anode arm on the top of the sample to ensure good contact.
• Enter Polishing&Etching menu. Set parameters: Voltage, flowrate, mask type and time.

For only polishing: Set only polishing time and polishing voltage. Do not set etching time and etching voltage, these should be zero “0”. Press start and operation will be completed automatically. The specimen must be washed after polishing operation is completed.

Polished surface and microstructure (Microstructure of Al-Cu-Steel)

For only etching: Set only polishing time and polishing voltage. Do not set etching time and etching voltage, these should be zero “0”. Press start and operation will be completed automatically. The specimen must be washed after etching operation is completed. Microstructure of etched surface can be seen as below:

Microstructure of etched surface (Microstructure of Al-Cu-Steel)

For automatic etching after polishing: Set polishing voltage, polishing time, etching voltage and etching time. Do not set etching time and etching voltage. Press start. Etching will be done automatically after polishing operation is completed. The specimen must be washed after etching operation is completed. For external etching: If polishing and etching electrolytes different than each other, in this case external etching unit can be used.

• Fill external etching unit with electrolyte.
• Connect cables of external etching unit to control unit.
• Enter External Etching menu. Set etching voltage and time.
• Hold the sample with scissors.
• Plunge the sample into the external etching unit. As soon as the sample contacts with the electrolyte the process will start automatically.
• As soon as the set etching time is reached an audible signal notifies the operator that the process is completed. Wash your specimen after etching is completed.