Ti-3Al-2.5V

Use slow-speed diamond saw with continuous coolant flow. Diamond saws are preferred for titanium alloys to minimize deformation and work hardening. Standard diamond blade (0.3-0.5 mm thickness) is appropriate. Use adequate coolant flow to prevent overheating and minimize work hardening. The reactive nature of titanium requires careful handling. Cutting speed: 150-250 RPM for most diamond saws. Apply light to moderate pressure - the material can work-harden if excessive pressure is applied. Avoid forcing the cut which can cause sample damage and work hardening. Leave adequate allowance (~1-2 mm) for grinding away the heat-affected zone and any deformation 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 material requires careful handling during mounting to avoid deformation. For critical applications, ensure the mounting material is compatible with the intended use environment.

The softness (140 HB) of Ti-3Al-2.5V requires careful grinding. Use standard SiC grinding papers with adequate water lubrication. Disc speed: 200-300 RPM. Apply light to moderate pressure (20-30 N per 30 mm sample) - the soft material is prone to smearing if too much pressure is applied. Use sharp, fresh grinding papers to minimize deformation.

Grinding sequence:

• 240 grit: Remove sectioning damage (20-40 seconds). Use moderate pressure to remove heat-affected zone.
• 320 grit: Remove previous scratches (20-40 seconds). Ensure complete scratch removal.
• 400 grit: Remove previous scratches (20-40 seconds). Ensure complete scratch removal.
• 600 grit: Remove previous scratches (20-40 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 softness 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 soft synthetic pad (e.g., TEXPAN) with light to moderate pressure (20-25 N per 30 mm sample). Start with 6μm to minimize damage. Monitor constantly for smearing and reduce pressure if any deformation is observed.
• 1μm diamond: 2-4 minutes on a soft synthetic pad (e.g., TEXPAN) with light pressure (15-20 N). Continue removing scratches from previous step.
• 0.05μm colloidal silica: 1-2 minutes on a soft 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 soft 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.

Ti-3Al-2.5V (Grade 9) is a lean alpha-beta alloy commonly used in aerospace tubing and bicycle frames. The low alloy content produces a predominantly alpha microstructure with minor beta phase, often in cold-worked and stress-relieved conditions. Kroll's Reagent (Chemical Etching) - Standard etchant:

• Composition: 2-3ml HF + 5ml HNO₃ + 100ml H₂O
• Preparation: Add acids to water slowly with stirring in a plastic container (HF attacks glass). Prepare fresh for best results.
• Application: Swab for 5-15 seconds. The low beta content means less contrast between phases than Ti-6Al-4V.
• Reveals: Alpha grains (light) with thin beta phase at grain boundaries (dark). In cold-worked tubing, reveals elongated grain structure and deformation texture.
• Rinse: Immediately with water, then ethanol. Dry with compressed air.

Modified Kroll's Reagent (Chemical Etching) - For fine-grained or cold-worked material:

• Composition: 1ml HF + 3ml HNO₃ + 100ml H₂O
• Application: Swab for 10-30 seconds. Less aggressive — preferred for cold-worked tubing where finer grain detail is needed.
• Reveals: Grain boundaries and deformation bands with better contrast control than standard Kroll's.

Etching Strategy:

• Start with Kroll's at 5 seconds for general examination
• Cold-worked tubing sections (longitudinal vs transverse) will show different grain aspect ratios
• For stress-relieved vs. fully annealed comparisons, Modified Kroll's gives more controlled contrast
• Grain size assessment per ASTM E112 after standardized etching

Safety: HF is extremely hazardous — always use in a fume hood with HF-rated gloves, face shield, and lab coat. Have calcium gluconate gel available. Store all HF solutions in plastic containers.