C17200 Beryllium Copper

Use slow-speed diamond saw or abrasive cut-off wheel designed for non-ferrous materials. Standard cut-off wheel (1.0-1.5 mm thickness) is appropriate. Use adequate coolant flow to prevent overheating and minimize deformation. Cutting speed: 150-250 RPM for most cut-off saws. Apply steady, moderate pressure - the material allows for reasonable feed rates. Avoid forcing the cut which can cause wheel wear and sample damage. Leave adequate allowance (~2-3 mm) for grinding away the heat-affected zone 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.

Hot compression mounting is acceptable if the part tolerates ~150-180°C and moderate pressure (2000-3000 psi for phenolic). Use phenolic or epoxy-phenolic resins. Ensure proper cooling under pressure to minimize shrinkage.

The hardness (380 HB) of C17200 Beryllium Copper 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:

• 240 grit: Remove sectioning damage (40-90 seconds). Use moderate pressure to remove heat-affected zone.
• 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 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.
• 1μm 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.
• 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 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.

C17200 Beryllium Copper is a precipitation-hardened alloy (Cu-1.9Be) with high hardness (380 HB in aged condition). The microstructure consists of an alpha copper matrix with gamma-phase (CuBe) precipitates that provide the high strength. Etching behavior varies significantly with heat treatment condition. Two primary etchants are recommended:

Ammonium Persulfate (Chemical Etching) - Primary choice for general microstructure:

• Composition: 10g (NH₄)₂S₂O₈ in 90ml H₂O
• Application: Immerse or swab for 10-30 seconds. The high hardness means slightly longer etch times than soft copper alloys. Prepare fresh.
• Reveals: Grain boundaries and general microstructure. Precipitation structure may require higher magnification to resolve.
• Rinse: Immediately with water, then ethanol. Dry with compressed air.

Copper No. 2 (Chemical Etching) - For revealing precipitate structure:

• Composition: 10g FeCl₃, 50ml HCl, 200ml H₂O
• Application: Immerse for 10-30 seconds, or swab for more controlled results.
• Reveals: Grain boundaries and gamma-phase precipitates. Better phase contrast than ammonium persulfate for this alloy. Useful for evaluating aging response.
• Rinse: Immediately with water, then ethanol. Dry with compressed air.

Safety: CAUTION — Beryllium is toxic. Avoid generating dust or fumes from the sample. Use appropriate containment during all preparation steps. Wear gloves, safety glasses, and lab coat. Use fume hood for all etching.