Hastelloy Etchants

Guide to etching Hastelloy and nickel-based superalloys. Covers Adler’s etchant and Weck’s reagent for revealing grain boundaries and microstructural features in these highly corrosion-resistant alloys.

Hastelloy Prep Guide Etchant Catalog

Hastelloy microstructure etched with Adlers etchant, 200X DIC

Alloy Classification & Preparation

Hastelloys are nickel-based superalloys with exceptional corrosion resistance, making them challenging to etch.

Common Designations

Hastelloy alloys classified by primary alloying elements and corrosion resistance.

View alloy series

B series: Ni-Mo alloys – HCl and reducing environment resistance
C series: Ni-Cr-Mo (C-4, C-22, C-276, C-2000) – Wide chemical resistance
G series: Ni-Cr-Fe – Phosphoric/sulfuric acid environments
Hastelloy N: Ni-Mo-Cr – Molten fluoride salt resistance
Hastelloy S: Ni-Cr-Mo – High-temperature oxidation resistance
Hastelloy X: Ni-Cr-Fe-Mo – Exceptional high-temperature strength

Typical Composition (Hastelloy X)

Major alloying elements and their roles in the microstructure.

View composition

Nickel: Remainder – FCC matrix structure
Chromium: 20.5–23% – Oxidation and corrosion resistance
Iron: 17–20% – Solid-solution strengthening
Molybdenum: 8–10% – Strengthening and corrosion resistance
Cobalt: 0.5–2.5% – High-temperature properties
Carbon: 0.05–0.15% – Grain boundary carbides

Preparation Tips

Hastelloy alloys are tough and work-harden readily during preparation.

View key considerations

Use low-speed precision cutting with adequate coolant
Use fresh abrasives to prevent smearing of the ductile matrix
Diamond polishing recommended for scratch-free surfaces
Final polishing with colloidal silica removes residual deformation
Electrolytic etching may be needed for highly resistant grades

Recommended Etchants

Due to high corrosion resistance, aggressive etchants or extended times may be required. For more guidance and the Materials Prep ELN etchant catalog, see Etchant Resources.

Etchant	Composition	Conditions	Applications
Adler’s Etchant	Ferric chloride: 45 g Copper ammonium chloride: 9 g Hydrochloric acid: 150 ml Distilled water: 75 ml	Immerse for several seconds Rinse in water Dry with alcohol	Very effective etchant for Hastelloy Reveals grain boundaries and general microstructure
Weck’s Nickel 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	Nickel-based alloys Reveals grain structure and microstructural details
Glyceregia	Glycerol: 10 ml Hydrochloric acid: 10 ml Nitric acid: 5 ml	Swab fresh solution only; do not store 5–60 seconds Rinse in water; dry with alcohol	General-purpose etch for Hastelloy and other Ni-base superalloys Reveals grain boundaries and gamma matrix structure WARNING: mix fresh; aged glyceregia can decompose with gas evolution
Kalling’s No. 2 (Waterless)	Cupric chloride: 5 g Hydrochloric acid: 100 ml Ethanol or methanol: 100 ml	Immerse or swab; seconds to minutes at 20°C Rinse in water; dry with alcohol	Ni-Cu and Ni-base superalloys (Inconel, Waspaloy) Reveals matrix grain structure and second phases
Marble’s Reagent	Copper sulfate (CuSO₄): 10 g Hydrochloric acid: 50 ml Distilled water: 50 ml	Swab or immerse 5–60 seconds Rinse in water; dry with alcohol	Nickel, Ni-Cu, and Ni-Fe superalloys Reveals matrix and carbide distribution
10% Oxalic Acid (electrolytic)	Oxalic acid: 10 g Distilled water: 100 ml	Electrolytic at 6 V DC, stainless cathode 15–60 seconds Rinse in water; dry with alcohol	Reveals grain boundaries and gamma-prime distribution in resistant Ni-base superalloys Effective when chemical etchants attack matrix non-uniformly

Troubleshooting

Common etching issues and how to resolve them.

No Visible Etching

Hastelloy’s corrosion resistance makes etching difficult. Try increasing immersion time or use stronger Adler’s etchant.

Over-etching

Surface appears too dark or pitted. Reduce etching time and monitor progress between short immersions.

Uneven Etching

Ensure sample surface is dry and free of polishing compounds. Use consistent swabbing motion.

Staining

Rinse immediately with water and dry with compressed air or alcohol to prevent oxide formation.

Poor Grain Boundary Contrast

Try Weck’s Nickel Reagent for improved grain structure, or consider electrolytic etching for resistant grades.

Etchant Shelf Life

Prepare fresh Adler’s etchant for each use. The ferric chloride solution degrades over time.