Titanium Sample Preparation

Introduction

Titanium and its alloys combine high strength-to-weight ratio with excellent corrosion resistance, making them essential in aerospace (Ti-6Al-4V airframe and engine components), biomedical (hip implants, pacemaker casings, dental work), chemical processing, and sports equipment. Per Don §11.6.2, metallographic preparation of titanium is fairly straightforward by conventional techniques; the harder problem is etching, where the same corrosion resistance that makes titanium useful also resists most reagents.

Ti-6Al-4V titanium alloy microstructure showing alpha and beta phases, etched with Kroll's reagent.

Sectioning

Per Don §11.6.2, use a MAXCUT MAX-C or MAX-I series blade. MAX-C is specifically the silicon-carbide / resin-rubber bonded blade designed for hard non-ferrous metals (titanium, zirconium); MAX-I is a thinner industrial alternative. Standard alumina blades (MAX-D, MAX-E, MAX-VHS) are formulated for steels and are wrong for titanium.

MAX-C silicon-carbide / resin-rubber bonded cut-off blade, designed for hard non-ferrous metals including titanium and zirconium. MAX-I is the industrial thin-blade alternative.

• Blade: MAX-C (preferred) or MAX-I for general titanium work. SiC abrasive resists the work-hardening and gummy behavior titanium exhibits against alumina blades.
• Coolant: Flood coolant continuously. Never dry-cut titanium. Fine Ti swarf is pyrophoric and can ignite. Water-based cutting fluid is standard.
• Feed rate: Slow, steady. Excessive force burns the blade and work-hardens the cut surface.
• Blade thickness: Thin (0.5-1.0 mm) precision blades minimize heat input and HAZ depth.
• Clean immediately after sectioning to remove cutting fluid and prevent contamination during mounting.

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

Mounting

Mounting provides edge retention and easier handling. For titanium, compression mounting with phenolic or epoxy resins works well. 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

1. Clean the sample thoroughly to remove cutting fluid and debris
2. Place sample in mounting press with appropriate resin
3. Apply pressure: 3000-4000 psi for phenolic, 2000-3000 psi for epoxy
4. Heat to 150-180°C and hold for 5-8 minutes
5. Cool under pressure to room temperature

Castable Mounting (also known as Cold Mounting)

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 heat that could affect titanium microstructure.

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

Grinding

Don §11.6.2 specifies a 5-step SiC progression from 240 grit through 1200 grit (P220 → P500 → P1200 → P2400 → P4000). The full sequence is needed because titanium work-hardens and smears under coarse abrasive; jumping grit steps leaves subsurface deformation that no amount of polishing fully removes.

Silicon carbide (SiC) grinding papers. The full P220 → P4000 progression is needed for titanium to control work-hardening and smearing. Rotate the sample 90° between each grit.

Grinding Sequence (Don §11.6.2)

1. 240 grit (P220) SiC: Water lubricant, 5-10 lb, 200/200 rpm head/base, grind until plane.
2. 360 grit (P500) SiC: Water, 5-10 lb, 200/200 rpm, 1 minute.
3. 600 grit (P1200) SiC: Water, 5-10 lb, 200/200 rpm, 1 minute.
4. 800 grit (P2400) SiC: Water, 5-10 lb, 200/200 rpm, 1 minute.
5. 1200 grit (P4000) SiC: Water, 5-10 lb, 200/200 rpm, 1 minute.

Important: Rotate the sample 90° between each grit to confirm complete scratch removal. Use water lubrication and maintain consistent 5-10 lb force. Clean the sample ultrasonically between steps to prevent contamination from coarser SiC particles carrying forward.

For more information on grinding supplies, visit our Silicon Carbide Grinding Papers collection.

Polishing

Polishing removes grinding scratches and prepares a mirror-like surface. For titanium, diamond polishing followed by oxide polishing typically yields excellent results. Use appropriate pads and maintain consistent pressure to avoid contamination and relief.

Polycrystalline diamond compound provides consistent cutting action for titanium alloys.

Various polishing pads for different polishing stages. Select pad hardness based on titanium alloy and polishing stage.

Don's handbook documents two polishing paths for titanium: a conventional mechanical path (§11.6.2) used for most aerospace and industrial work, and an attack-polishing path (§11.6.3, contributed by Medtronic) used for biomedical titanium where high-contrast phase imaging is required. Pick the path by goal.

Standard Path: Conventional Polishing (Don §11.6.2)

Use for: Routine grain size, alpha/beta phase identification, alpha-case measurement, weld analysis, fatigue/failure analysis. The default for aerospace and industrial titanium work.

1. 6 µm DIAMAT diamond on TEXPAN polishing pad: DIALUBE Purple Extender lubricant, 5-10 lb, 200/200 rpm head/base, 3 minutes.
2. 1 µm DIAMAT diamond on GOLDPAD polishing pad: DIALUBE Purple Extender, 5-10 lb, 200/200 rpm, 2 minutes.
3. 0.05 µm Nanometer alumina on ATLANTIS polishing pad: 5-10 lb, 100/100 rpm, 1 minute.
4. Rinse thoroughly with water, then ethanol; dry with compressed air.

Pad Map & Parameters Summary (Standard Path)

Attack Polishing Path (Don §11.6.3, biomedical)

Use for: Biomedical titanium (hip implants, pacemaker casings, dental work) where enhanced microstructural contrast is needed. Contributed to Don's handbook by Jim Hallquist at Medtronic. The chemo-mechanical action of colloidal silica with H₂O₂ and Kroll's reagent simultaneously polishes and etches, producing surfaces with strong phase contrast under both brightfield and polarized light without a separate etch step.

1. 180 grit SiC paper: Water, 5-10 lb, 200/200 rpm, until plane.
2. 240 (P220) grit SiC paper: Water, 5-10 lb, 200/200 rpm, 1 minute.
3. 320 (P360) grit SiC paper: Water, 5-10 lb, 200/200 rpm, 1 minute.
4. 9 µm DIAMAT diamond on TEXPAN polishing pad: 5-10 lb, 200/200 rpm, 10 minutes.
5. Attack polish: 100 mL SIAMAT colloidal silica + 20 mL H₂O₂ (3%) + 10 mL Kroll's reagent. 5-10 lb, 100/100 rpm, 10 minutes.

Safety: The attack-polish slurry contains HF (from the Kroll's reagent component). Mix in a fume hood with HF-rated gloves and face shield. Calcium gluconate gel within reach. Discard after each session; don't store the mixed slurry.

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

Etching

Titanium and its alloys resist most metallographic etchants because the same passive oxide that gives titanium its corrosion resistance also protects it from chemical attack. Successful titanium etchants are nearly all HF-based. Kroll's reagent is the standard first choice for general microstructure imaging; specialty reagents handle specific tasks (color etching, beta-phase revelation, Cu-bearing alloys, etc.).

Microetchants for Titanium (Don's Table LI)

• Kroll's Reagent: first choice for Ti alloys; very good general etch revealing α/β phases and grain boundaries.
  • Composition: 1-3 mL HF + 2-6 mL HNO₃ + 100 mL DI water
  • Use: Swab 3-10 seconds, or immerse 10-30 seconds. Standard reagent for Ti-6Al-4V, CP-Ti, most alpha-beta alloys.
• Keller's Reagent (for Ti): etches Ti alloys (note: same reagent name as aluminum's Keller, but different recipe).
  • Composition: 1 mL HF + 3 mL HCl + 5 mL HNO₃ + 190 mL DI water
  • Use: Immerse 3-10 seconds.
• R-Etch: specialized for Ti-Al and Ti-Al-Zr alloys.
  • Composition: 25 mL HF + 18.5 mg benzalkonium chloride + 35 mL ethanol + 40 mL glycerin
  • Use: Swab up to 20 seconds, or immerse up to 90 seconds with agitation.
• Smith Reagent: for β-Ti alloys heat-treated below β-transus; reveals grain boundaries.
  • Composition: 60 mL propionic acid + 20 mL HNO₃ + 10 mL HF
  • Use: Swab.
• Gallagher Reagent: for Ti-Cu alloys specifically.
  • Composition: 60 mL lactic acid + 20 mL HNO₃ + 10 mL HF + 10 mL DI water
  • Use: Immerse 3-10 seconds.
• Gurevich Reagent: reveals β phase in Ti alloys.
  • Composition: 10 mL HF + 10 mL HNO₃ + 10 mL H₂SO₄ + 1 g succinic acid
  • Use: Heat to 40-50 °C; immerse 20-180 seconds.
• Ogden & Holden Reagent: differentiates phases in α-β alloys; HF-free.
  • Composition: 1-4 mL HCl + 1 mL H₂SO₄ + 95-98 mL DI water
  • Use: Use boiling, 3-10 minutes. Slower but avoids HF if equipment is unavailable.

Color (Tint) Etchants

• Weck's Tint Etch (for Ti): colors α grains and twins according to crystal orientation; excellent for grain-orientation imaging. Note: Weck's for Ti is a different reagent than Weck's for Al.
  • Composition: 5 g ammonium bifluoride (NH₄HF₂) + 100 mL DI water
  • Use: Immerse at 20 °C for a few seconds. Don's Fig 11-49 uses this for wrought Ti.
• Beraha's Tint Etch (for Ti): for as-cast Ti alloys; colors α matrix blue or green, intermetallics yellow or dark brown.
  • Composition: 2-3 g sodium molybdate + 5 mL HCl + 1-2 g ammonium bifluoride + 100 mL DI water
  • Use: Immerse at 20 °C until surface is colored.

Stain Removal

Titanium etchants frequently leave stains, particularly on alpha-rich regions. Don's recommended stain-removal recipe:

• Composition: 1 mL HF + 2 mL HNO₃ + 50 mL H₂O₂ + 47 mL DI water
• Use: Immerse sample for several seconds. Works on most titanium and titanium alloys.

Macroetchants (Don's Table LII)

• General Ti macroetch: 50 mL DI water + 40 mL HNO₃ + 10 mL HF (40%). Etch 5-8 min at 60-80 °C. (HF content may be reduced.) For Ti, Ti-base, and Ti-Al-Mo alloys.
• Flow lines and defects: 75 mL DI water + 15 mL HNO₃ + 10 mL HF. Etch ~2 min.
• General α + β: 50 mL HCl + 50 mL DI water. Etch ~2 min.
• Macro contrast: 30 mL DI water + 10 mL HF (40%) + 60 mL H₂O₂ (30%). Swab until desired contrast.
• Welded seams: 200 mL DI water + 10 mL HF (40%) + 10 g Fe(NO₃)₃·9H₂O. Etch seconds to minutes at 50-60 °C.

Etching Procedure

1. Ensure sample is clean and dry. Residual colloidal silica from polishing gives mottled etch results.
2. Apply etchant per the recipe: swab for short exposures (Kroll's, Keller's, R-etch), immerse for color etches (Weck's, Beraha's) and boiling/heated etches (Ogden-Holden, Gurevich).
3. Etch for the recommended time. Start at the short end of any range.
4. Rinse immediately with water, then ethanol. For HF-containing etchants, neutralize and dispose of waste per HF protocol.
5. Dry with compressed air. Do not wipe.

Tip: Most HF-containing titanium etchants lose activity within 30-60 minutes of mixing; make small batches fresh. If a Kroll's etch leaves stains, use the stain-removal recipe above and re-examine; if the structure is now too faint, repeat the etch.

For more information on etchants, visit our Etchants collection.

Troubleshooting

Common Issues and Solutions

• Scratches reappear after Kroll's etch (smeared/work-hardened layer): Classic Ti problem. The polish produced a smeared layer that hides scratches; the etch dissolves the smear and the scratches reappear. Fix: extend the 1 µm DIAMAT step (3-4 min instead of 2) at lighter force (5-6 lb); confirm the GOLDPAD is fresh. If scratches persist, return to 1200 grit (P4000) SiC with fresh paper.
• Scratches remaining after polish: Insufficient time at one of the SiC grinding steps, or skipped grit. Don's 5-step ladder (240→360→600→800→1200) must be run in full; skipping leaves subsurface deformation that the diamond steps cannot remove in reasonable time.
• Stains after Kroll's etch: Common with Ti. Use the stain-removal recipe (1 mL HF + 2 mL HNO₃ + 50 mL H₂O₂ + 47 mL water, immerse a few seconds). Re-etch if structure becomes too faint.
• Mottled or uneven etch: Residual colloidal silica or polishing debris on the sample. Rinse thoroughly with ethanol before etching. Verify the sample is fully dry.
• No etch / weak structure: Etchant past its useful life (HF-containing reagents drop in activity within 30-60 minutes of mixing). Mix fresh and retry. Or switch from swab to immerse for harder alloys.
• Pitting after etching: Time too long or etchant too aggressive. Reduce time, dilute etchant, or switch to the HF-free Ogden-Holden boiling reagent.
• Alpha-case ambiguous on imaging: The brittle oxygen-enriched surface layer (typical 5-100 µm) sometimes etches more slowly than the bulk. View at 200× brightfield after Kroll's etch; case appears lighter, more featureless. For quantitative case-depth measurement per ASTM E1558 / AMS 2249, use Weck's tint etch with polarized light for better contrast at the case/bulk boundary.
• Relief around second phases or interstitials: Over-polishing or too soft a pad at the final step. Reduce alumina-on-ATLANTIS time to 30-45 seconds; confirm ATLANTIS is the pad (not a higher-nap final).
• Cross-contamination with iron particles: Ti can pick up Fe from prior steel samples on the same equipment. Use dedicated wheels/pads for Ti when possible; clean ultrasonically between sample types.
• Surface oxidation between polish and etch: Ti forms a passive oxide quickly. Etch promptly after final polish; if delay is unavoidable, store in desiccator and re-polish briefly on alumina-on-ATLANTIS before etching.
• Smeared structure on biomedical Ti: Conventional polishing leaves smear that hides fine microstructural features. Switch to the attack-polishing path (Don §11.6.3): 9 µm DIAMAT on TEXPAN for 10 min, then SIAMAT silica + H₂O₂ + Kroll's for 10 min. The chemical action lifts smear that mechanical polishing alone cannot.

Additional Reading

• Zipperian, D.C. Metallographic Handbook, §11.6.2 (Titanium Conventional) and §11.6.3 (Titanium Attack Polishing, contributed by Jim Hallquist, Medtronic Inc.). PACE Technologies, Tucson, AZ. The house reference. The grinding, polishing, and etchant recipes in this guide come from these sources.
• Vander Voort, G.F. Metallography: Principles and Practice. ASM International. Comprehensive reference for Ti etchant procedures and color metallography techniques.
• Petzow, G. Metallographic Etching, 2nd ed. ASM International. Comprehensive reference for Kroll's, Keller's, Weck's, Beraha's, and specialty Ti reagent formulations.
• ASM Handbook, Vol. 9: Metallography and Microstructures. ASM International. Titanium preparation, etching, and phase identification.
• ASTM E407 — Standard Practice for Microetching Metals and Alloys (titanium etchants section).
• ASTM E1558 — Standard Guide for Electrolytic Polishing of Metallographic Specimens (and alpha-case evaluation reference).
• AMS 2249 — Chemical Check Analysis Limits, Titanium and Titanium Alloys (alpha-case depth specifications).
• ASTM E3 — Standard Guide for Preparation of Metallographic Specimens.
• ASTM E112 — Standard Test Methods for Determining Average Grain Size.