×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Inconel 625 etching
2

Inconel 625 etching

Inconel 625 etching

(OP)
Hi,

Could anybody help with a suitable etchant for revealing grain strucutre for grain size determination in Inconel 625, I'm guessing mixed acids is the way to go? I am aware a bit trial and error would be the best solution but as I am waiting for the components I thought I would ask the question.

Thanks

RE: Inconel 625 etching

We use electrolytic oxalic acid, it give enough GB definition to be usable.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Inconel 625 etching

(OP)
Thanks guys, I done a bit reading up on some of Vander Voorts papers. One strange thing with the samples is MC type carbides are visible in the un etched condition, however, in the areas the material has been deformed they appear to have disperesed very finely/or gone completely! Is this possible!?

RE: Inconel 625 etching

(OP)
also I have tried many of the advised etching techniques with no results

RE: Inconel 625 etching

It is extremely nasty and safety gear and good ventilation is a must, but aqua-regia with 30% H2O2 will often work. Mix the aqua-regia then make occasional additions of the H2O2 very carefully. The reaction is extremely vigorous. Good luck and be careful. The first time I used it the fume hood was not up to the task and the lungs took a burning.

RE: Inconel 625 etching

1. etching for precipitates is much different than etching for GB.
2. you can have little to no precipitates, it depends on anneal temp, cooling rate, and cold work

Can you see the acicular phase without etch (polarized or DIC)?

What is the product for and what is its thermo-mechanical history?

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Inconel 625 etching

The structure does not look like inconel 625 or no inconel 625 I have ever seen. I don't think you have etched this structure correctly as I can see any grain boundaries. I think the acicular structure is a polishing artefact. Etching inconel 625 is sometimes difficult and requires some experimentation to get it to etch properly. Try 15 mL HCl, 10 mL acetic acid, 10 mL HNO3, The acid has to be made up fresh as it goes off.

RE: Inconel 625 etching

(OP)
Ed, Unfortunately I do not know the background behind the material, also, i dont have the facility for dic or polarized light. metaljon, I have tried with mixed acids etchant with no luck

RE: Inconel 625 etching

Not sure if you've tried this combo, but 15mL HCl, 10mL acetic acid, 5mL HNO3, and 2 drops glycerol revealed the grain structure in this 625 micrograph.



Source: ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys.

RE: Inconel 625 etching

That does not look like cold work, looks like solidification structure (e.g. welding).

RE: Inconel 625 etching

I would agree, this appears to be more of a dendritic microstructure.

RE: Inconel 625 etching

(OP)
It appears only on the outer few mm. Would you agree it coukd be possibly from localised heating and slow cooling?

RE: Inconel 625 etching

Or from serious heavy machining.
Looks more like deformation than structure.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Inconel 625 etching

Well your sample looks etched to me. Etching is a bit like making a cake you have to experiment with the acid mixture and concentration. A little a bit of glycerol may help. The photo shows evidence of a weld structure. Has this been weld repaired?

RE: Inconel 625 etching

(OP)
i was saying i had no luck with the mixed acid etchant. this was etched electrolytically

RE: Inconel 625 etching

You certainly see weld (dendritic) structure and grain structure in the adjacent base metal (probably heat affected zone) when you zoom in on the #2 picture. Looks like electrolytically-applied oxalic works (in that picture), but you may want to photograph at higher mag.

Aaron Tanzer
www.lehightesting.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources