Tungsten Carbide (WC)

Use diamond saw with continuous coolant flow. Diamond saws are essential for cutting hard ceramic materials. Standard diamond blade (0.3-0.5 mm thickness) is appropriate. Use adequate coolant flow to prevent overheating and minimize thermal shock. Cutting speed: 100-200 RPM for most diamond saws. Apply light to moderate pressure - the very hard material requires careful handling to avoid cracking. Avoid forcing the cut which can cause blade damage and sample cracking. Leave adequate allowance (~1-2 mm) for grinding away any damage from cutting.

Cold mounting with epoxy resin is preferred to avoid heat that could affect the microstructure. Use a low-shrinkage epoxy resin for best edge retention. Ensure complete cure before grinding to prevent edge rounding and maintain sample integrity. The very hard material requires careful handling during mounting to avoid cracking. For cutting tool and wear-resistant applications, ensure the mounting material provides adequate edge retention.

The very-hardness (2400 HV) of Tungsten Carbide (WC) requires careful grinding. Use standard SiC grinding papers with adequate water lubrication. Disc speed: 200-300 RPM. Apply light to moderate pressure (30-40 N per 30 mm sample) - the hard material may require longer grinding times. Use sharp, fresh grinding papers to minimize deformation.

Grinding sequence:

• 120 grit: Remove sectioning damage (40-90 seconds). Use moderate pressure to remove heat-affected zone.
• 240 grit: Remove previous scratches (40-90 seconds). Ensure complete scratch removal.
• 320 grit: Remove previous scratches (40-90 seconds). Ensure complete scratch removal.
• 400 grit: Remove previous scratches (40-90 seconds). Ensure complete scratch removal.
• 600 grit: Remove previous scratches (40-90 seconds). Ensure complete scratch removal.

Always rotate the specimen holder 90° between steps to ensure complete scratch removal. Use complementary rotation (platen and holder same direction, different speeds) rather than contra-rotation to minimize deformation. Adequate water lubrication is critical - avoid drying during grinding which can cause smearing.

The very-hardness requires careful polishing. Use diamond polishing with appropriate polishing pads for each stage. Apply light to moderate pressure throughout to prevent deformation.

Diamond polishing sequence:

• 6μm diamond: 2-4 minutes on a medium-hard synthetic pad (e.g., TEXPAN) with light to moderate pressure (30-40 N per 30 mm sample). Start with 6μm to minimize damage. The hard material may require longer polishing times.
• 3μm diamond: 2-4 minutes on a medium-hard synthetic pad (e.g., TEXPAN) with light pressure (25-35 N). Continue removing scratches from previous step.
• 1μm diamond: 2-3 minutes on a medium-hard synthetic pad with lighter pressure (25-35 N). These pads provide gentle material removal.
• 0.05μm colloidal silica: 1-2 minutes on a high-napped final polishing pad (e.g., MICROPAD) with very light pressure. This removes any remaining fine scratches and prepares the surface for etching. Monitor for relief - reduce polishing time if excessive relief develops.

Use appropriate polishing lubricants. The very-hard material means polishing times should be sufficient but not excessive - avoid over-polishing which can cause relief and affect grain boundary revelation. Monitor the surface frequently under the microscope to check for smearing or excessive relief.

Pure tungsten carbide (without cobalt binder) is etched similarly to WC-Co cemented carbides. Murakami's Reagent is the standard etchant. An HCl/H₂O₂ mixture can also be used for rapid attack. Murakami's Reagent - Standard etchant for WC:

• Composition: 10 g K₃Fe(CN)₆ + 10 g KOH + 100 ml water. Prepare fresh — solution degrades with use.
• Application: Immerse for 3–10 min at room temperature. May require heating to 50–60°C for pure WC (no binder phase).
• Reveals: WC grain boundaries, eta phase (if present), and free carbon. Grains appear as angular, geometric shapes with clear boundaries.
• Rinse: Water, then ethanol. Dry with warm air.

HCl + H₂O₂ (30%) - Rapid chemical etchant for WC:

• Composition: 10 ml HCl + 10 ml H₂O₂ (30%). Mix fresh immediately before use.
• Application: Immerse for seconds to minutes. Monitor carefully — can be aggressive.
• Reveals: WC grain structure. More aggressive than Murakami's — useful for heavily sintered or resistant grades.
• Rinse: Immediately with water, then ethanol. Dry with compressed air.

Etching Strategy:

• Start with Murakami's Reagent for controlled, reproducible results
• Use HCl/H₂O₂ for rapid grain boundary revelation or when Murakami's is insufficient
• For WC with cobalt binder, see the WC-Co cemented carbide page for additional etchants (10% HCl for selective Co removal)

Safety: Murakami's Reagent contains potassium ferricyanide — do NOT acidify (releases HCN gas). HCl/H₂O₂ mixture generates chlorine gas — prepare and use in a fume hood. Wear gloves, safety glasses, and lab coat.