Titanium Etchants

Complete guide to selecting and applying etchants for titanium and titanium alloys. The strong oxide layer on titanium requires aggressive etchants to reveal alpha and beta phases, grain boundaries, and prior-beta grain boundaries.

Titanium Prep Guide Etchant Catalog

Cast titanium alloy microstructure showing alpha-beta phases

Alloy Classification & Preparation

Understanding the alloy phase composition helps select the right etchant. Titanium alloys are classified by their stabilizing elements and resulting microstructure.

Alloy Classification System

Titanium alloys are grouped by phase stability determined by alloying elements.

View alloy types

Alpha alloys: Contain alpha stabilizers (Al, O, N, C). Good creep resistance, weldable, non-heat-treatable
Near-alpha alloys: Predominantly alpha with small amounts of beta stabilizers. High-temperature applications
Alpha-beta alloys: Both alpha and beta stabilizers (e.g., Ti-6Al-4V). Heat treatable, most widely used
Near-beta alloys: High beta stabilizer content. High strength, good formability
Beta alloys: Contain beta stabilizers (V, Mo, Nb, Fe, Cr). Heat treatable, high strength, good cold formability
Commercially pure (CP): Grades 1–4, varying oxygen content. Corrosion resistance, biocompatibility

Common Designations

Key titanium alloy grades and their typical applications.

View grade designations

Grade 1–4 (CP Ti): Unalloyed titanium with increasing oxygen content and strength
Grade 5 (Ti-6Al-4V): Most common titanium alloy; aerospace, medical implants
Grade 9 (Ti-3Al-2.5V): Moderate strength; tubing, aerospace hydraulic systems
Grade 12 (Ti-0.3Mo-0.8Ni): Improved corrosion resistance; chemical processing
Grade 23 (Ti-6Al-4V ELI): Extra low interstitials; medical implants, cryogenic applications
Ti-6Al-2Sn-4Zr-2Mo: High-temperature alpha-beta alloy; jet engine components
Ti-10V-2Fe-3Al: Near-beta alloy; high strength aerospace forgings

Preparation Tips

Titanium is reactive and prone to forming a deformed surface layer during grinding.

View key considerations

Use water-based coolants during sectioning to prevent heat damage and oxidation
Avoid excessive grinding pressure to minimize subsurface deformation
Final polishing with colloidal silica or alumina is recommended to remove the disturbed layer
Clean thoroughly between preparation steps to prevent cross-contamination
Store prepared samples in a desiccator to prevent surface oxidation before etching
Hydrofluoric acid requires special safety precautions: use HF-rated PPE

Recommended Etchants

While Kroll's reagent is the most commonly used general-purpose etchant for titanium, specific alloy systems and microstructural features may require specialized etchants. For PACE's full etchant catalog and the Materials Prep ELN, see Etchant Resources.

Etchant	Composition	Conditions	Applications
Kroll's Reagent	Nitric acid: 2–3 ml Hydrofluoric acid: 1–2 ml Distilled water: 100 ml	Immerse or swab for 3–10 seconds Rinse in water Dry with alcohol	Most widely used general-purpose etchant for titanium alloys Reveals alpha-beta microstructure, grain boundaries, and prior-beta grain boundaries
HF-HNO₃-Glycerol	Hydrofluoric acid: 5 ml Nitric acid: 30 ml Glycerol: 60 ml	Swab for 5–20 seconds Rinse in water Dry with alcohol	Beta-phase titanium alloys and Ti-6Al-4V Provides slower, more controllable attack than Kroll's; glycerol moderates the reaction
Weck's Titanium Reagent	Potassium permanganate: 10 g Sodium hydroxide: 2.5 g Distilled water: 250 ml	Immersion or swabbing at 20 °C Rinse in water Dry with alcohol	Color etchant for titanium alloys and other resistant metals Reveals grain boundaries, phases, and microstructural features Particularly effective for differentiating alpha and beta phases

Troubleshooting

Common etching issues and how to resolve them.

Over-etching

Surface appears too dark or pitted. Reduce etching time by 50% and monitor under the microscope. Titanium etches rapidly once the oxide layer is breached.

Under-etching

Grain boundaries not clearly visible. Increase etching time incrementally or ensure etchant is freshly prepared. The passive oxide layer can resist initial attack.

Uneven Etching

Ensure sample is completely dry before etching and maintain consistent immersion or swabbing motion. Alpha and beta phases etch at different rates.

Staining

Rinse immediately with water after etching and dry with compressed air to prevent water spots and residual chemical deposits.

Poor Phase Contrast

Try Weck's reagent for color contrast between alpha and beta phases, or adjust Kroll's reagent concentration for better differentiation.

Surface Artifacts

If scratch patterns appear after etching, return to polishing and ensure all deformation is removed before re-etching. Titanium is prone to subsurface damage.