Metallographic Etching Technical InformationIntroduction
Etching is a process for revealing the structure of the material, common etching techniques include:
- Chemical
- Electrolytic
- Thermal
- Plasma
- Molten salt
- Magnetic
Common Etchants (sold by PACE Technologies)
There are a number of more common etching solutions. Several of them are listed in the folowing table.
| Etchant | Composition | Conc. | Conditions | Comments |
|---|---|---|---|---|
| Adler Etchant | Copper ammonium chloride Hydrochloric acid Ferric chloride, hydrated DI Water |
9 grams 150 ml 45 grams 75 ml |
Immersion is recommended for several seconds | For etching 300 series stainless steel and other superalloys |
| Al-NaOH Etchant | NaOH Distilled water |
25 grams 250 ml |
Immersion is recommended for several seconds | For etching aluminum alloys |
| Ammonium Persulfate Etchant | (NH4)2S2O8 Distilled water |
50 grams 245 ml |
Immersion is recommended for several seconds | For brasses, especially brasses containing Cobalt |
| ASTM No. 30 | Ammonia Hydrogen Peroxide (3%) DI Water |
62.5 ml 125 ml 62.5 ml |
Mix Ammonia and water before adding peroxide. Must be used fresh. Swab 5-45 seconds | For etching copper, copper alloys and copper-silver alloys |
| ASTM 97 | KOH |
187.5 gram 245 ml |
Electrolytic at 2.5 V for few seconds | Fe-Cr-Ni alloys - Stains siga and chi yellow to red brown, ferrite gray to blue gray, carbides barely touched, austenite not touched |
| ASTM. No. 157 | CrO3 HCl Distilled water |
31.25 grams 187.54 ml 62.5 ml |
Immersion is recommended for several seconds | Hastelloy |
| Beraha's | Distilled water Na2S2O3 7.5 grams K2S2O5 |
250 ml 25 grams 7.5 grams |
Immersion is recommended for several seconds | For etching tool steel - Colors ferrite, martensite, bainite, and pearlite. Cementite unaffected |
| Carpenters Stainless Steel Etch | FeCl3 CuCl2 Hydrochloric acid Nitric acid Ethanol |
8.5 grams 2.4 grams 122 ml 6 ml 122 ml |
Immersion etching at 20 degrees Celsius | For etching duplex and 300 series stainless steels |
| Copper No.1 | Nitric acid Distilled water |
125 ml 125 ml |
Immersion etching at 20 degrees Celsius | Copper and brass Etchant |
| Copper No.2 | Distilled water HCl FeCl3 |
200 ml 50 ml 10 grams |
Immersion etching at 20 degrees Celsius | Copper and brass Etchant |
| CU-PASS-SOL | CuSO4-5H2O H2SO4 Distilled water |
40 grams 1.5 ml 245 ml |
This test is recommended for the detection of free iron on the surface of austenitic stainless steels in the 200 and 300 series, precipitation hardened stainless steels, and ferritic 400 series stainless steels having a minimum of 16 % chromium. A copper color on the metal surface (brown or pinkish) indicates that surface iron is still present and thus the part failures the test. If no reaction occurs it is considered a test pass | |
| Dichromate | H2SO4 Distilled water Ssaturated NaCl K2Cr2O7 |
36 ml 445 ml 18 ml 8.9 grams |
Cu-Sn (tin bronze) | |
| Fry's Etchant | HCl CuCl2, 75 ml d Distilled water Denatured alcohol |
100 ml 12.5 grams 75 ml 65 ml |
Fry's reagent for martensitic and precipitation hardenable grades of stainless steel | |
| Inconel Etchant | Solution A: |
50 ml 40 ml 75 ml 15 ml 35 ml 50 ml |
Do not STORE MIXED SOLUTIONS IN CLOSED CONTAINERS.Use Fresh and discard after mixing. | Macro etchant for Inconel-type alloys on NiCr and Ni-Fe-Cr basis. Etchant for Ni-Nb, Ni-Ta, Ni-Si, Ni-Co-Cr alloys |
| Kalling's No. 2 | CuCl2 Hydrochloric acid Ethanol |
5 grams 100 ml 100 ml |
Immersion or swabbing etch at 20 degrees Celsius | For etching duplex and 400 series stainless steels and Ni-Cu alloys and superalloys. |
| Kellers Etch | Distilled water Nitric acid Hydrochloric acid Hydrofluoric acid |
190 ml 5 ml 3 ml 2 ml |
10-30 second immersion. Use only fresh etchant | Excellent for aluminum and titanium alloys. |
| Klemm's Reagent | Sodium thiosulfate solution Potassium metabisulfite |
250 ml Saturated 5 grams |
Etch for a few seconds to minutes | For etching alpha-beta brass, bonze, tin, cast iron phosphides, ferrite, martensite, retained austenite, zinc and steel temper embrittlement. |
| Klemm's 2 Reagent | Sodium thiosulfate solution Potassium metabisulfite |
250 ml Saturated 25 grams |
Etch for a few seconds to minutes, heating to 40°C enhances the etching rate | For etching copper, cast iron and tin. Ferrite (blue or red), martensite (brown), cementite and austenite unaffected. |
| Kroll’s Reagent | Distilled water Nitric acid Hydrofluoric acid |
92 ml 6 ml 2 ml |
Swab specimen up to 20 seconds |
Excellent for titanium and alloys. |
| Lepito's Etchant | Solution A: (NH4)2 S2O8 Distilled Water; Solution B: FeCl3 HCl Solution C: HNO3 |
25ml |
Follow mixing directions listed on the product | Wrought stainless steel |
| Marble's Reagent | CuSO4 Hydrochloric acid Water |
10 grams 50 ml 50 ml |
Immerse or swab for 5-60 seconds. |
For etching Ni, Ni-Cu and Ni-Fe alloys and superalloys. Add a few drops of H2SO4 to increase activity. |
| Murakami's | K3Fe(CN)6 KOH Water |
10 grams 10 grams 100 ml |
Pre-mix KOH and water before adding K3Fe(CN)6 |
Cr and alloys (use fresh and immerse); iron and steels reveals carbides; Mo and alloys uses fresh and immerse; Ni-Cu alloys for alpha phases use at 75 Celcius; W and alloys use fresh and immerse; WC-Co and complex sintered carbides. |
| Nital | Ethanol Nitric acid |
100 ml 1-10 ml |
Immersion up to a few minutes. | Most common etchant for Fe, carbon and alloys steels and cast iron - Immerse sample up from seconds to minutes; Mn-Fe, MnNi, Mn-Cu, Mn-Co alloys. |
| Oberhoffers | Solution A: Ethanol, Distilled water FeCl3 SnCl2) Solution B: Distilled water HCl |
|
Use fresh | Steels and special steels. Fe-enriched areas appear dark |
| Picral | Ethanol Picric acid |
100 ml 2-4 grams |
Seconds to minutes Do not let etchant crystallize or dry –explosive |
Recommended for microstructures containing ferrite, carbide, pearlite, martensite and bainite. Also useful for magnetic alloys, cast iron, high alloy stainless steels and magnesium. |
| Ralphs etchant | Distilled water Methyl alcohol HCl CuCl2 FeCl3 |
62.5 ml 125 ml 62.5 ml 1.25 grams 4.4 grams |
Seconds to minutes | Ferritic stainless steels |
| Schantz Etchant | Solution A: |
5 ml 10 ml 110 ml 17 grams 30 ml 30 ml 40 ml 20 ml |
Seconds to minutes | Nickel and cobalt |
| TI-AP-16 | SiO2, 43 ml NH4OH, 16 ml 30% H2O2 |
432 ml 43 ml 16 ml |
Apply to polishing pad, rinse after use | Enhances the polishing rates and improves surface finishes for titanium alloys |
| Vilella’s Reagent | Picric Acid Hydrochloric acid Ethanol |
1 gram 5 ml 100 ml |
Seconds to minutes | Good for ferrite-carbide structures (tempered martensite) in iron and steel |
| Waterless Kallings | CuCl2, 125 ml HCl, Denatured alcohol | 6.25 gm 125 ml |
Seconds to minutes | Waterless Kalling's reagent; for iron-base and nickel-base superalloys |
| Weck's | 7.5 grams ammonium bifluorides HCl Distilled water |
4.5 grams 10 ml 240 ml |
Seconds to minutes | Weck's tint etch for Ti and alloys. Alpha grains and twins colored according to orientation |
| Winsteards | Picric acid, 10 ml |
2 grams 10ml 200 ml 5 ml 5 drops |
Seconds to minutes | Low carbon steel - austentic grain boundaries |
Etchant Database
Etching Product Descriptions
| Description | Common Stainless Steels etchants | Catalog Number |
|---|---|---|
| Adlers etchant | Very effective for etching austenitic 300 series stainless steels (250 ml) | ADLERS |
| Carpenters | 300 Series Stainless Steel Etchant (250 ml) | CARPENTERS |
| Kalling's No. 2 | Martensitic 400 series stainless steels (250 ml) | KALLINGS No. 2 |
| Frys Reagent | Precipitation hardened stainless steels (250 ml) | FRYS Reagent |
| Description | Common Copper and Brass etchants | Catalog Number |
|---|---|---|
| ASTM No. 30 | Copper etchant (250 ml) | ASTM No. 30 |
| Copper No. 1 | Copper & Brass (nitric acid and DI water) (250 ml) | COPPER No. 1 |
| Copper No. 2 | Copper & Brass (HCl and ferric chloride) (250 ml) | COPPER No. 2 |
| Klemms | Stain etch for brass (250 ml) | KLEMMS |
| Description | Most common Steel etchants | Catalog Number |
|---|---|---|
| 2-8% Nital | Most common etchant for non-heat treated or welded steels (250 ml) | NITAL-2 to NITAL-8 |
| Picral | Heat treated steels (250 ml) | PICRAL |
| Copper No. 2 | Copper & Brass (HCl and ferric chloride) (250 ml) | VIELLA'S |
| Description | Most common Aluminum and Titanium etchants | Catalog Number |
|---|---|---|
| Kellers | Most common etchant for aluminum alloys (250 ml) | KELLERS |
| Kroll's | Most common etchant for titanium (250 ml) | KROLLS |
| Titanium Attack Polish | Used as a CMP polishing compound for titanium (500 ml) | TI-AP-16 |
| Description | Nickel, Iron, Chromium alloys | Catalog Number |
|---|---|---|
| Marble's | Nickel, nickel-iron alloys (250 ml) | MARBLES |
| Murakami's | Chromium alloys (250 ml) | MURAKAMIS |
| Waterless Kalling's | Iron and nickel base alloys (250 ml) | WATERLESS KALLINGS |
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