Hello,
Is there any historical information on shear and tensile values for abradable coatings? More specific, 308 nickel graphite. Is there a correlation between the tensile and shear strength of this coating?

Thank you,
Kim

Hi Kim

to the Surface Engineering Forum.

I would think that there is some form of correlation in coating tensile strength between the perpendicular and parallel directions (referenced to substrate) of the coating. Usually the parallel direction has higher strength then the perpendicular. Or are we talking about bond strength tests in which case the substrate preparation will be a big variable, along with test methods used.

I have no information, but I'm sure someone must have looked into this at sometime. If I find anything I will come back. Are you looking at this for purely academic interest or for a practical purpose?

Thank you Gordon,

My question is very practical. Invariably the bond strength test for Metco 450, used with the application of 308 coating, was not performed. So we are left with several parts that have 450/308 applied and no test data to verify the integrity of the coating. We tried working backwards by calculating the shear strength of the coating. A test strip was mounted to the 308 coating and a shear load was applied. However, we are unable to obtain data on shear or tensile strengths of abradable coating. Thus my dilema. Any ideas?

Thanks again.

Hi Kim

Not total sure I understand. I assume you have test pieces for hardness or metallography left over, but no tensile bond strength test pieces. You conduct shear strength tests on test pieces because that suits the test piece shape. Then you want to be able relate shear strength to tensile bond strength. If that is so, could tell me the dimensions of your test pieces. To be honest, I think you would be better to try tensile bond strength tests on these test pieces, may end up being a little unconventional. I think even if you found information on correlation, at best it would only give extremely rough approximations and doubt whether you could rely on them. But maybe I?ve got hold of the wrong end of the stick

Hi Gordon,
The problem is, I don't even have test pieces. Just production parts coated with 308/450. The coating is applied to the seal bore of the part with an approx. 4 inch diameter. We applied a shear loaded to the part and are trying to correlate the value we obtained to some industry standard. But we can't seem to find any data on strengths (tensile or shear) of abradable coatings. In all likelihood the parts will have to be reprocessed. I sure appreciate your input.

Thank you,
Kim

Hi Kim

I can't find anything on tensile bond strength for this coating. Normally only hear of superficial Rockwell hardness testing and metallography as routine testing. Suspect (not sure, never tried it) there may be problem with getting sufficient adhesion with adhesives used in normal tensile bond strength test piece due to "dirty" nature of graphite loaded coating.

Hi Kim,

I have experiences in testing abradable coatings in our repair shop, particularly Metco 308 (85 : 15 Ni-Graphite) and Metco 307 (75 : 25 Ni-Graphite) for application on aircraft engine components.

I got a reference that says Metco 308 can have a tensile bond strength of minimum 2000 Psi.
As for Metco 307, one of the engine components manuals requires a minimum of 750 Psi fot the tensile bond strength.
Both can be obtained from the work performed in our repair shop.

Just like Gordon said, the normal tests for abradable coatings are Hardness and Metallographic.
The product bulletin gives a value of 30 - 50 HR15Y for Metco 307 and 50 - 70 HR15Y for Metco 308.
The typical features that should be look into in the metallographic analysis are : Delamination, Integrity, Transverse cracks and Porosity , and sometimes Dispersal of Nickel Graphite constituents.

I think you can make test pieces along with your production load.
I mean , you can attach several test panels as close as possible to your part, or you can spray them later on with the same process parameters (parameter records and standard practices should be done of course).

Hope this helps,

Have a good day,
MaDiLa

Hi Madila

Thank you for that information. My suspicion that there could be problems with getting bond strength test adhesives to stick to these coatings is flawed Your bond strength values certainly seem to be realistic for this type of coating (intentional weak and flawed coating for abradability)

Hi Madila

I thought it best to move your query to a new thread. http://www.gordonengland.co.uk/sef/split...t-116.html

Quote: [split] Abradable coatings

Hi Gordon,

Just read your reply today.

I hope you don't mind my continuing the discussion on the abradable coatings.

I want to ask you the possible causes of getting inconsistent hardness values from time to time.
I mean what critical factor can give significant contribution to this inconsistency.
We spray the specimens of Ni 75 - Graphite 25 coating as an abradable layer for compressor rotor of aircraft engine.
Although we always obtain hardness values within the range as recommended by the OEM and/or the material manufacturer (i.e. 30 - 50 HR15Y ) , there is still an inconsistency in the test results.
Sometimes they are all above 40 HR15Y , but lately they are all in the lower range i.e. 30 - 40 HR15Y only.
This makes us difficult to release the test result as the representative of the sprayed part, in a way that we would only find out the actual quality of our thermal spray process result after the part is installed and tested as a complete engine.
If the part has not released with top quality, we are afraid it will abrade easily and during engine testing (high pressure, high temperature) will affect other parts which are very costly.

Hope you or others can help me again this time and share the knowledge.

Thank you.

for parallele coating choose f1000 if you r working with robot but for perpondicular coating i think you ll have rotation of subsrate then till 50 diametre u can choose f32 or f24 it depend your desired thikness ,after more your diameter is big ,less is your speed

hvofhamid Wrote:for parallele coating choose f1000 if you r working with robot but for perpondicular coating i think you ll have rotation of subsrate then till 50 diametre u can choose f32 or f24 it depend your desired thikness ,after more your diameter is big ,less is your speed

Sorry hvofhamid you have completely lost me there. I do not understand your reply or the relevance to this thread.

Gordon Wrote:

hvofhamid Wrote:for parallele coating choose f1000 if you r working with robot but for perpondicular coating i think you ll have rotation of subsrate then till 50 diametre u can choose f32 or f24 it depend your desired thikness ,after more your diameter is big ,less is your speed

Sorry hvofhamid you have completely lost me there. I do not understand your reply or the relevance to this thread.

hello gordon ,my english is really poor ,don t mind please.evry time i can t explain what i mean .could you have a translation service french to english

Hi hvofhamid

My French is very poor compared to your English

http://world.altavista.com/ may be worth a try.

I tried it on my last post.

Quote:Sorry hvofhamid you have completely lost me there. I do not understand your reply or the relevance to this thread.

to French

Quote:Hvofhamid d?sol? vous m'avez compl?tement perdu l?. Je ne comprends pas votre r?ponse ou la pertinence avec ce fil.

and back again to English

Quote:Sorry Hvofhamid me completely lost you there. I do not include/understand your answer or the relevance with this wire.

Used with care could be useful

Hi all,
I have spraied Metco 450/308 coating by Metco 6P flame spray system. I test the Tensile Bond strength and coating Microstructures to control quality for the coating. The Tensile bond strength are usually in 1500~ 2500 Psi.

Hope that this information will help to you.

Best regards,

William

Thanks to Madila and William for useful data on tensile bond strength. Even with this information I think it will still be very difficult to formulate a practical correlation between shear and tensile bond strength for Kim's purposes.