Grain Boundary Carbide Network In725

[Mett87]

I have a section of In725 that appears to have a nearly continuous carbide network at the grain boundaries.

Is this typical for this grade?

Heat treatment was:-
1040c for 11hr/air cool
730c for 12hr/furnace cool to 620c hold for 8hr/air cool

Hardness 37HRC

Thanks in advance.

 

[metengr]

I think you should spend some time to search and review the article below;

MICROSTRUCTURES AND THE STRUCTURE STABILITY OF INCONEL 725,A NEW AGE—HARDENABLE CORROSION RESISTANT SUPERALLOY
J.X.Dong[1], M.C.Zhang[1], S.K.Mannan[2]

 

[EdStainless]

And check out the papers by Special Metals.
First of all you need a way to know if they are carbides or some other phase.
And then you need to look at samples prior to HT.
And then you can identify what it really is, and decide if it matters (properties, corrosion resistance).

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Plymouth Tube

 

[Mett87]

I cant find that exact paper, however, I did find one that has suggested M23C6 and M6C type are typically precipitated at the grain boundarys as originally thought. I can't find any reference to the amount of precipitation typical for specific ageing times/temps.

 

[metengr]

http://www.amse.org.cn/EN/abstract/abstract3285.shtml

 

[Mett87]

This was the paper I found

http://www.tms.org/superalloys/10.7449/2001/01-5107-345.pdf

 

[kumkumvijay]

According to the TTT diagram, the purpose and expected microstructure for the HT cycle is as below:

Annealing cycle :

1040C for 11 hrs à it will produce Eta phase and if its very long exposure time then sigma phase formation will happen, however with in 11hrs it will not form sigma phase.

Each annealing cycle has its own impact on mechanical properties.

Aging cycle for 20 Hrs:

1.       730C for 12 Hrs à M23C6/ M6C formation in grain boundary with gamma prime & double prime phase in the matrix.

2.       620C for 8 Hrs à hold inside the furnace to complete the total 20 Hrs cycle.

Checking:
If you want to check it then you can use SEM/EDX analysis for chemical composition checking.
Please refer the paper below

http://www.tms.org/superalloys/10.7449/2001/01-5107-345.pdf

 

[EdStainless]

Are you sure that they grain boundaries were clean after the solution anneal?
What about properties? Does the material have the ductility that it should?

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Plymouth Tube

 

[Mett87]

Unfortunately I don't have a comparison for after the solution anneal or any data regarding mechanical properties, the section is also too small to perform testing on. Kimkumvijay - that is the paper I referenced.

 

[Mett87]

http://s30.postimg.org/i6ojrebst/image.jpg

 

[EdStainless]

It doesn't look right to me.
What is the etch?

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Plymouth Tube

 

[Mett87]

HCL/H2O2 nothing else would touch it!

Tried gleyceriga and mixed axids.

 

[Mett87]

Heres another micrograph etched with modified glyceriga electrolytically to show the precipitates

http://s23.postimg.org/5n0ggh293/glycerol.jpg[/img][/url