- Selection of the sample- Select a representative sample that accurately depicts the material's unique microstructural characteristics. Based on the needs of the analysis, the dimensions and form of the sample are to be taken into consideration.
- Sectioning- Section the sample using a precision cutting machine. The sections are 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 the sample is oriented correctly to get the analysis plane desired.
- 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, use 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).
- Etching- Different etchants are required for different metals and alloys. The etching procedures for commonly used alloys are summarized below.
Aluminum (Al) Alloys
• Purpose: Reveal grain boundaries, precipitates, and phase distribution.
• Etchant: Keller’s reagent- 95 mL H₂O + 2.5 mL HNO₃ + 1.5 mL HCl + 1 mL HF
• Procedure: Immerse in Keller’s reagent for 5–10 s and rinse with distilled water and dry.
Brass (Cu-Zn Alloys)
• Purpose: Highlight grain structure and phase separation (α, β phases).
• Etchant: Ferric chloride solution- FeCl3 + HCl + water
• Procedure: Immerse in FeCl3 solution for 5–20 s (depending on alloy composition). and rinse with water and ethanol.
Bronze (Cu-Sn Alloys)
• Purpose: Reveal grain boundaries, α and δ phases, and inclusions.
• Etchant: Ammonium persulfate (5 g in 100 mL water)
• Procedure: Etch briefly (5–30 s) until microstructure is visible. Rinse with water and ethanol, and then dry.
Titanium (Ti) and Ti Alloys
• Purpose: Highlight α and β phases, twins, and grain structure.
• Etchant: Kroll’s reagent- 2–3 mL HF + 5–10 mL HNO₃ + 92–93 mL H₂O
• Procedure: Immerse in Kroll’s reagent for 5–15 s (short immersion to avoid over-etching). Rinse thoroughly in water, followed by alcohol, and dry.
- 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. Ensure the sample is completely dry before examining the specimen under a microscope.
- Microscopic examination- Place the prepared specimen 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, applying a protective layer (like lacquer) can be preferred to stop oxidation.
