Metallographic Preparation of Titanium and Its Alloys
Resumen y preparación

Titanium and Ti-alloys are valued for high strength-to-weight ratios, corrosion resistance, and biocompatibility, making them essential in fields like aerospace, medicine, and chemical processing. To verify that manufacturing and heat treatment have produced the desired microstructure, the metallographic preparation and analysis of titanium and its alloys are essential. This guide outlines the complete preparation process from cutting and mounting to grinding, polishing, and etching and adds practical tips for achieving reproducible, artifact-free results.

Topics

• Overview
• Metallographic preparation of titanium
  • Cutting and mounting
  • Grinding and polishing
  • Etching
• FAQ

Metallographic Preparation of Titanium and Its Alloys

Metallographically preparing titanium is notoriously challenging and requires a tailored approach for each step. Titanium’s high ductility means it is prone to plastic deformation and smearing during grinding or polishing if one is not careful.

Cutting and mounting

Cutting Ti and Ti-alloys

Titanium is a relatively tough and ductile metal, which makes it susceptible to smearing, burr formation, and thermal damage during sectioning. Standard abrasive cut-off wheels, especially those based on aluminium oxide, tend to perform poorly on titanium, often generating excessive heat (noticeable by its characteristic burning smell) and leaving a rough surface or pronounced burr.

For clean, damage-free cuts, it is essential to use a cut-off wheel specifically designed for titanium, such as a silicon carbide (SiC)-based wheel with a resin bond. We recommend our Ti-A wheel, which is engineered for titanium alloys like Ti-6Al-4V and Ti-5Al-2.5Sn, as well as other refractory metals such as molybdenum, tantalum, and niobium. Always use adequate coolant flow to keep the sample and cutting area cool and to flush away reactive titanium swarf. This not only protects the microstructure but also helps reduce the risk of dust ignition and tool wear.

To minimize heat generation and surface deformation, a slow feed rate is crucial. A cutting speed in the range of 0.1–0.25 mm/s is typically recommended. For harder titanium alloys or critical specimens, the feed rate can be further reduced to prevent heat buildup and ensure structural integrity at the cutting edge.

Proper specimen fixation is also key: the sample must be securely clamped on both sides of the cut line to prevent vibration, deflection, or sudden break-off during the final phase of the cut. Thin sheets or plates should be backed with a supporting material, such as a fibre-reinforced plate or HPL board, to avoid bending or collapsing during sectioning.

Mounting Ti and Ti-alloys

In production environments, large titanium components are often prepared without mounting due to their size and handling stability. However, for small, precision-manufactured parts, mounting is essential to ensure accurate, repeatable results and protect sample edges during preparation.

Both hot and cold mounting methods are suitable for titanium. For hot mounting, we recommend EPO BLACK, a mineral- and glass-filled epoxy resin-based material that provides excellent edge retention, minimal gap formation, and high plane parallelism, ideal for critical metallographic analysis. Alternatively, EPO MAX, with similar properties but shorter cycle times.

When heat exposure must be avoided, cold mounting is preferred. Options include KEM 20, a transparent, methylmethacrylate-based resin suited for target preparation, or KEM 15+, which offers very low shrinkage and high edge retention, making it ideal for fine structures and edge-sensitive samples.

Grinding and polishing

Titanium's ductility and low thermal conductivity make it particularly sensitive to mechanical deformation, smearing, and surface damage during grinding and polishing. If not properly controlled, preparation can easily introduce a deformed surface layer that obscures the true microstructure and is difficult to remove. The objective is to create a flat, scratch-free, and deformation-free surface that accurately reveals the grain structure, phase distribution, and other key features. This requires a careful balance of mechanical and chemical action, along with appropriate consumables and preparation parameters tailored to titanium. Achieving this requires well-matched consumables, precise process control, and in many cases, a chemically assisted final polish.

To minimize deformation and smearing during preparation, planar grinding of titanium should begin with a moderately fine SiC paper or foil, avoiding overly coarse abrasives. This helps limit surface damage and ensures easier removal of deformation in later steps. Polishing is typically done in two stages: first with an abrasive diamond suspension (typically 9 µm), such as DiaComplete Poly, a water-based suspension for efficient material removal; and second with a chemical-mechanical final polish using Eposil F (0.1 µm), mixed with 35% hydrogen peroxide in a 5:1 ratio. (Safety note: Always wear appropriate personal protective equipment when handling peroxide.) This final step is crucial for eliminating the disturbed surface layer and revealing a clean, undistorted microstructure.

The following tables present recommended preparation methods:

- For commercial pure titanium (grade 1-4)

- For titanium-based alloys:

^{* * Eposil F must be mixed with hydrogen peroxide (35%) in a ratio of 5:1 (safety advice: use personal protective equipment)}

^{** ** Depends on the alloy}

Etching

After final polishing, titanium samples often appear mirror-like and may reveal faint structural contrast under polarized light. However, to clearly observe features such as grain boundaries, phase differences, and deformation structures, chemical etching is typically required.

Several etchants are commonly used for titanium and its alloys, each with specific strengths:

• Kroll’s reagent is the most widely used etchant for titanium, particularly effective for revealing the microstructure of α+β alloys such as Ti-6Al-4V. It provides strong contrast between α and β phases and is available pre-mixed from many suppliers.
• Keller’s reagent is a general-purpose etchant for titanium alloys, suitable for routine microstructural evaluation.
• Weck’s reagent is a colour etchant used to visualize the microstructure of titanium and its alloys through interference colouring. It selectively stains α and β phases, while hydride and nitride needles, oxygen-enriched diffusion zones, and β-phase regions typically remain white. This makes it especially useful for analysing grain orientation and distinguishing microstructural features not visible with standard etching.

The table below summarizes these three common etchants and their typical applications:

Safety Notice: Acids must be used with caution. Wear protective equipment and follow lab safety guidelines.

Always handle hydrofluoric acid with extreme caution, as even small exposures can be life-threatening!

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