Posted by Jeff on April 15, 2008 at 09:53:52:
In Reply to: Etchant for AMS5599 (Inconel625) LBMR posted by Krzysztof Maślak on April 14, 2008 at 06:24:56:
Here are some suggestions that were posted in response to a similar question. I found them by searching the archives.
"Alloy 625 is a fairly corrosion resistant grade. At Carpenter, we etched 625 and the age hardenable version, CA625 Plus, with a mix of 15 mL HCl - 10 mL acetic acid - 10 mL nitric acid. Use reagent grade acids, mix fresh, DO NOT STORE!!! Etch by swabbing up to about 2 minutes. This etch works fine, but the specimen must be properly prepared." -GV
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"Lucas Reagent for general structure of Superalloys and Stainless Steels
Composition: HCl 150ml, Lactic Acid 85+% 50ml, Oxalic Acid 3g
Use: For Nickel, Iron, and Cobalt based superalloys 10 to 20 volts DC at 0.2 Amps for 10 to 30 seconds depending on which alloy and the state of the sample.
For Stainless Steel, Austenitic Grade Swab on for several seconds or add 50% more lactic acid 3 to 6 Volts DC at 0.2 Amps 10 Seconds
For Ferritic and Precipitation Hardenable grades Use original formula 3 to 6 Volts DC at 0.2 Amps for 10 seconds or less. Outlines delta ferrite, brings out grain boundaries, and reveals martensite." - GL
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"We get good results on revealing the grain structure of Inco 625 with:
10ml FeCl3 8% soln
50ml conc HNo3
4ml conc HNo3
4ml conc lactic acid
I would suggest swab etching" - M.A.B.
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"With most of the Ni alloys I have had good success with the modified Kalling's etch. I call it Superalloy etch. 6 ml H2O, 60 ml HCl, 6 g CuCl2." - FH
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"I have yet to see truly good results on a superalloy without final polishing with acidic alumina or colloidal silica (not a neutral solution, Struers OP-S is preferable). Also, if the 'wavy' surface appears after electroetching, I'm not surprised as that is a common occurrence with electrolytic applications.
This etchant could fall into the glyceregia category but it has worked for me,
15mL HCl
10mL acetic acid
5mL HNO3
2 drops glycerol" - JA