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Metallographic Etching

Metallographic Etching

Etching

Specific Etchants  ]  Common Etchants  Etchant Database CD ]  Product Description  [ Home ]


Etching is a process for revealing the structure of the material, common etching techniques include:

  • Chemical
  • Electrolytic
  • Thermal
  • Plasma
  • Molten salt
  • Magnetic
The two most common techniques are chemical and electrochemical etching. Chemical etching is typically a combination of either an acid or base with an oxidizing or reducing agent in a solute such as an alcohol. Electrochemical etching is a combination of chemical etching with an electrical voltage/current.

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Common Etchants

There are a number of more common etching solutions. Several of them are listed in the folowing table.

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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Etchant Database CD

For more specific etchants, PACE Technologies offers an CD etchant database containing over 2200 etchants.

Metallographic Etchant Database CD   Metallographic Technical CD
Metallographic etchant and training CD
Metallographic Etchant CD Results Screen   Metallographic Preparatoin Basics CD
Etchant database search result   Metallographic training basics

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ETCHING PRODUCT DESCRIPTIONS

ETCHING / SPECIMEN PREPARATION

Description

Quantity

Catalog Number

Etchant / Specimen preparation CD

each

CD-ETCH


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