Cermets & Technical Glasses Sample Preparation

Introduction

Cermets (ceramic-metal composites) and technical glasses are important materials in cutting tools, wear parts, optics, and electronics. Common cermets include tungsten carbide-cobalt (WC-Co, ~1500-2000 HV), titanium carbide-nickel (TiC-Ni), and other carbide-metal composites. Technical glasses include borosilicate glass, fused silica, quartz, and specialty optical glasses (~500-800 HV). Both material families are hard and brittle, requiring diamond abrasives, consistent pressure, and careful handling to reveal the true microstructure without cracking, chipping, or pullout.

Sectioning

When sectioning cermets and technical glasses, use a very slow cutting speed to minimize heat generation and prevent cracking. A cutting speed of 20-50 RPM is typically appropriate - much slower than most other materials. These materials are extremely hard and brittle, requiring very careful handling to prevent chipping and cracking. Thermal shock during cutting can cause catastrophic failure, so adequate cooling is absolutely critical.

Diamond wafering blades are essential for cermets and technical glasses due to their extreme hardness. Use precision wafering saws with diamond blades. Apply very light, steady pressure and use adequate coolant to prevent thermal shock and cracking.

• Use diamond wafering blades - diamond is essential due to the extreme hardness of these materials
• Use precision wafering saws for best results with these brittle materials
• Apply very light, steady pressure - avoid any sudden changes that could cause cracking
• Use adequate coolant continuously to prevent overheating and thermal shock
• Cut very slowly (20-50 RPM) to prevent cracking and chipping
• Allow the blade to do the cutting - avoid forcing or excessive pressure
• Clean sample immediately after sectioning to remove cutting fluid and debris
• Inspect the cut surface carefully for any signs of cracking or damage

For more information on sectioning blades, visit our Abrasive Blades collection.

Mounting

Mounting provides edge retention and easier handling. For cermets and technical glasses, compression mounting with phenolic resins works well due to their hardness and provides good edge support. Castable mounting with epoxy is also suitable and avoids potential heat-related issues. Ensure the sample is thoroughly cleaned before mounting to prevent contamination.

Compression Mounting (Recommended)

1. Clean the sample thoroughly to remove cutting fluid and debris
2. Place sample in mounting press with phenolic resin (provides good edge support for hard materials)
3. Apply pressure: 3000-4000 psi for phenolic
4. Heat to 150-180°C and hold for 5-8 minutes
5. Cool slowly under pressure to room temperature to prevent thermal shock

Castable Mounting (also known as Cold Mounting) — Alternative

1. Clean and dry the sample thoroughly
2. Place in mounting cup with epoxy resin
3. Allow to cure at room temperature (typically 4-8 hours)

Castable mounting avoids the heat and pressure that could cause thermal shock in brittle materials.

Important: Cermets and technical glasses are very hard, so phenolic mounting resins provide better edge support than softer resins. However, if the material is particularly sensitive to heat or thermal shock, castable mounting may be preferred. Cool slowly after compression mounting to prevent thermal shock that could cause cracking.

For more information on mounting equipment, visit our Compression Mounting Equipment page.

Grinding

Cermets and technical glasses require different grinding approaches. Because cermets (1500-2000 HV) are close in hardness to SiC abrasive (~2500 HV), standard SiC papers remove material very slowly and wear rapidly. Diamond grinding discs and diamond lapping films are strongly recommended for cermets. Technical glasses (500-800 HV) can be ground with SiC papers, though diamond lapping films produce less subsurface damage on these brittle materials.

Metal-bonded diamond grinding discs provide effective material removal on hard cermets where SiC papers are inefficient.

Cermets (WC-Co, TiC-Ni)

1. 70 or 45 μm diamond grinding disc: Remove sectioning damage (2-5 minutes). Metal-bonded discs are preferred for initial stock removal
2. 30 μm diamond lapping film: Intermediate grinding (2-4 minutes)
3. 15 μm diamond lapping film: Fine grinding (2-3 minutes)
4. 9 μm diamond lapping film: Final grinding (1-2 minutes)

Technical Glasses

1. 320 grit SiC paper: Remove sectioning damage (60-90 seconds). Use light pressure to prevent fracture
2. 600 grit SiC paper: Intermediate grinding (60-90 seconds)
3. 15 μm diamond lapping film: Fine grinding (1-2 minutes). Transition to diamond minimizes subsurface damage
4. 9 μm diamond lapping film: Final grinding (1-2 minutes)

Rotate the sample 90° between each step to verify complete scratch removal. Use water as a lubricant and maintain consistent, moderate pressure. Clean the sample thoroughly between steps to prevent cross-contamination.

Polishing

Diamond abrasives are required throughout all polishing steps — other abrasives are not effective on these materials. Expect extended polishing times (often 2-3x longer than metals) and use consistent, moderate pressure to avoid chipping or carbide pullout.

Polycrystalline diamond compound provides aggressive material removal on hard cermets and glasses.

Various polishing pads and cloths for different polishing stages. Start with hard cloths for coarse diamond polishing, then progress to softer cloths for final polishing steps. Consistent pressure is critical.

Diamond Polishing

1. 9 μm diamond: 6-10 minutes on a hard cloth (e.g., Texpan, Cermesh)
2. 3 μm diamond: 6-10 minutes on a medium-hard cloth
3. 1 μm diamond: 4-6 minutes on a soft cloth

Final Polishing

1. 0.05 μm colloidal silica: 3-5 minutes on a soft cloth
2. Rinse thoroughly with water and dry with compressed air

Tip: Clean thoroughly between steps to prevent contamination. For cermets, use harder cloths (Texpan, Cermesh) during coarse steps to minimize carbide pullout, then transition to softer cloths for final polishing. Monitor edges for chipping and reduce pressure if needed. WC-Co and TiC-Ni may require times at the upper end of the ranges above.

For more information on polishing supplies, visit our Diamond Abrasives and Polishing Pads collections.

Etching

Etching reveals the microstructure. Cermets typically use Murakami's reagent or similar etchants to reveal the carbide phase and binder distribution. Technical glasses typically do not require etching, but can be examined in the as-polished condition. Some glasses may be etched with HF-based solutions, but this requires extreme caution and proper safety equipment.

Common Etchants for Cermets and Technical Glasses

• Murakami's Reagent: For WC-Co cermets. Mix 10g K₃Fe(CN)₆, 10g KOH, 100ml H₂O. Etching time: 10-60 seconds. Most commonly used for tungsten carbide-cobalt cermets. Reveals the WC phase and Co binder distribution.
• Modified Murakami's: For TiC-Ni and other cermets. Mix 10g K₃Fe(CN)₆, 10g NaOH, 100ml H₂O. Etching time: 10-40 seconds. Similar to standard Murakami's but with NaOH instead of KOH.
• Various Acid Mixtures: For TiC-Ni and other cermets. Composition varies by specific cermet type. Etching time: 10-30 seconds. Consult specific references for exact compositions.
• No Etching: Technical glasses typically do not require etching - examine in as-polished condition. The microstructure of glasses is usually visible without etching.
• HF-based Solutions (Glasses): Very dilute HF solutions (0.5-2%) may be used for some glasses, but this requires extreme caution. Warning: HF is extremely hazardous and requires proper safety equipment including calcium gluconate gel for first aid.

Etching solutions and reagents for cermets and technical glasses. Common etchants include Murakami's reagent (WC-Co cermets) and modified Murakami's (TiC-Ni cermets). Technical glasses typically do not require etching. Etching time for cermets typically ranges from 10-60 seconds. Warning: HF-based etchants for glasses are extremely hazardous and require proper safety equipment.

Etching Procedure

1. Ensure sample is clean and dry
2. Apply etchant with cotton swab or immerse sample (depending on etchant)
3. Etch for 10-60 seconds (time varies by etchant and material - cermets may require longer times)
4. Immediately rinse with water, then alcohol
5. Dry with compressed air

Tip: For WC-Co cermets, Murakami's reagent is the most commonly used etchant and typically provides good results. Technical glasses usually do not require etching as their microstructure is visible in the as-polished condition. If etching is needed for glasses, use very dilute HF solutions (0.5-2%) with extreme caution and proper safety equipment. Cermets may require longer etching times than typical metals due to their chemical resistance.

For more information on etchants, visit our Etchants collection.

Troubleshooting

Common Issues and Solutions

• Cracking: Excessive pressure or thermal shock during sectioning/mounting. Use lighter pressure, very slow cutting speeds (20-50 RPM), and ensure adequate coolant flow. Thermal shock is a major concern with brittle materials. Cool slowly after compression mounting to prevent thermal shock.
• Chipping: Too aggressive grinding or excessive pressure. Use finer starting grits (240 or 320) and diamond abrasives. Maintain consistent, moderate pressure. Avoid sudden pressure changes that could cause chipping.
• Scratches remaining: Insufficient polishing time - these materials are extremely hard and require extended polishing times (often 2-3x longer than typical materials). Increase polishing duration significantly. Ensure you're using diamond abrasives - SiC will not be effective for these materials.
• Pullout (cermets): Cermet particles pulling out during polishing. Use softer cloths and lighter pressure. For cermets, the binder phase (Co, Ni) may polish faster than the carbide phase, causing pullout. Adjust cloth hardness and pressure to minimize this.
• Poor edge retention: Consider using phenolic mounting material which provides better edge support for hard materials. Ensure proper mounting pressure and temperature.
• Inconsistent polishing: Use diamond abrasives throughout - SiC is not effective for these extremely hard materials. Ensure consistent pressure and adequate polishing time. These materials require much longer polishing times than typical metals.
• Slow material removal: Cermets and technical glasses are extremely hard, so material removal will be much slower than softer materials. This is normal - be patient and allow adequate time for each step. Diamond abrasives are essential.
• Edge chipping during polishing: Use softer cloths for final polishing steps and reduce pressure slightly. Hard cloths can cause chipping at sample edges, especially for brittle technical glasses.
• Insufficient etching: Cermets may require longer etching times or more aggressive etchants due to their chemical resistance. Try increasing etching time or using a more concentrated etchant solution.