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Metallographic Etchants

Metallographic Etching

COMMON ETCHANTS

CAUTION:Safety is very important when etching. Be sure to wear the appropriate protective clothing and observe all WARNINGS on chemical manufacuters MSDS. Also review the COMMENTS and CONDITIONS Section for each etchant.

Recommended Etchants

Metallographic micrograph of aluminum Metallographic micrograph of high carbon steel
Metallographic micrograph of Bronze Metallographic micrograph of stainless steel
Metallographic micrograph of cast iron Metallographic micrograph of tin
Metallographic micrograph of copper Metallographic micrograph of zinc
Metallographic micrograph of low carbon steel Metallographic micrograph of BeO

The following table lists the most commonly used etchants

Etchant

Composition

Conc.

Conditions

Comments

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.

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

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.

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.

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.

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.

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.

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.

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


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