Sectioning, Mounting, Grinding, Surface Preparation, Technique for Polishing and Etching of Materials (including Electropolishing, tint etching etc.)
- Sample selection
Select a representative sample that accurately depicts the material's unique microstructural characteristics. Based on the needs of the analysis, take the sample's dimensions and form into consideration.
- Sectioning
Section the sample using a precision cutting machine. The sections ought to be divided perpendicularly to the interest areas. Use a coolant or lubricant when cutting to avoid overheating and sample damage.
- Mounting
Insert the divided sample into a mounting substance (often a thermosetting resin) to sustain and uphold the specimen's integrity in the ensuing stages. Make sure you're oriented correctly to get the analysis plane you want.
- Grinding
Using abrasive papers or grinding stones, coarsely grind the mounted sample to get rid of extra material and create a smooth, even surface. To improve the surface finish, go to finer abrasive sheets.
- Polishing
To achieve a mirror-like surface, polish the sample with polishing papers of varying grit sizes to eliminate scratches and grinding marks. For the last stages of polishing, use a polishing cloth dipped in a polishing suspension (usually alumina or colloidal silica).
- Electropolishing
To get rid of any impurities that could impede the electropolishing process, such as grease, oils, or oxides, the workpiece is carefully cleaned. The electrolyte bath is submerged with the cleaned workpiece. The application of a DC current starts the dissolution of the metal surface. An even and smooth surface is the consequence of the removal of metal ions from high points, peaks, and asperities in a preferred location. Any leftover electrolyte solution is rinsed from the workpiece.
- Etching
An essential first step in exposing the material's microstructure is etching. Choose the right etchant according to the content being examined. Chemical solutions such as picral and nital are frequently used as etchants. To ensure even and regulated etching, apply the etchant for a predetermined amount of time.
- Tint etching
The stock tint-etching solution is prepared in a beaker and activated according to the prescribed protocol, or the required tint etchant is freshly mixed using the appropriate formulation. Typically, 100–200 mL of solution is used in a small glass or polyethylene beaker. Prior to etching, the sample must be thoroughly cleaned, as any surface residue can inhibit uniform film formation.
The cleaned specimen is placed face-up at the bottom of the beaker, as many tint etchants require an immersion time of approximately 60–90 s. During etching, the solution is gently swirled without splashing. Depending on the material and etchant composition, surface coloration generally begins within 20–40 s. The beaker is then left undisturbed until the surface color transitions from red to violet.
After etching, the sample is removed, rinsed with warm water, sprayed with ethanol, and dried. Care is taken to avoid touching the etched surface. For tint etchants with rapid reaction kinetics, the sample is held with tongs and gently agitated in the solution until sufficient surface darkening is achieved. The resulting macroscopic surface appearance is typically grey to black.
- Rinsing and drying- To get rid of any last bits of debris or etchant, thoroughly rinse the polished and etched sample with water or an appropriate solvent. Use a gentle, lint-free cloth or a stream of air to dry the specimen.
- Mount removal
If required, use a heated mount remover or an appropriate solvent to remove the mounting material.
- Final cleaning
Use a mild detergent or solvent to clean the sample and get rid of any leftover contaminants. Before examining the specimen under a microscope, make sure it is completely dry.
- Microscopic examination
The prepared specimen should be placed on the microscope stage. For a thorough examination of the microstructure, use the proper magnification and lighting. Take pictures or draw sketches for your documentation.
- Analysis and reporting
Conduct any required measurements or analyses in accordance with the study's goals. Note down all the results, including phases, microstructural characteristics, and any anomalies.
- Preservation (optional)
If the specimen needs to be preserved for an extended period, think about applying a protective layer (like lacquer) to stop oxidation.
