low tensile strength problem

[raviswanadha]

Hi ,
we are presently under qualification for plasma spray coating for Aero engine manufacturers. We have recently spray Metco 450NS with 9MB Gun and metco specified parameters on button samples and sent out for testing.
The testing reported
1. Tensile bond strength 4650 psi as against requirement of 5000min
2. Porosity > 5 % requirement porosity < 3%
3. Interface seperation observed .

We resprayed the same coating on sleeve , bond coat 45ons and top coat metco 6240. When tested
1. tensile bond strength 5650psi
2. Porosity max 5%
3. NO INTERFACE seperation.

My question is could any one suggest a fixture for holding the samples for coating and also what could be the reason for low bond strength and high porosity.

regards

[kschewe]

how thick are you spraying the bond strength testing samples. For 5000 psi, you should be under .015

[raviswanadha]

how thick are you spraying the bond strength testing samples. For 5000 psi, you should be under .015

We are coating 380 microns as per astm c 633 requirements
Regards

[loriolo]

I think there is something wrong, please check the sand blasting operation, for correct roughness and profile, then check gun hardware and geometry, and before spray check the flame geometry while the powder is on, of course pointing the gun trough an exhaust system, and last, Metco parameters are a start point, then you can change them in order to obtain the specified values.

[kriskros]

Hello All

I have a question related to bond strength test nature. I have two laboratories which can perform this test. One of them is NADCAP approved and is performing test according to ASTM C633 with 1,27mm/min feed. Second is local lab that I'm familiar with, but they are performing test with feed 5mm/min - they have old style tensile machine ant that's the minimum speed that they can set. When I'm testing only adhesive (for example FM1000) in both labs I think I can get very similar results. I'm not sure how it's looks like with coatings - sometimes the differences between results gained in two labs are significant. Can anybody tell what is the influence of faster feed on results that I can receive while testing coating for example Metco 81VF-NS? It would be good to have this local lab as a reference for example during implementation of new coatings and then, after achieving good micro structure and bond strength test results, perform final approval in NADCAP lab.

[kriskros]

Hello All

Any suggestions about the influence of feed to test results?

[Gordon]

Hi kriskros

The faster you pull them the higher the result I think is the normal trend. Whether that would show a significant difference between 1mm/min to 5mm/min I'm not sure.

[kriskros]

Hi kriskros

The faster you pull them the higher the result I think is the normal trend. Whether that would show a significant difference between 1mm/min to 5mm/min I'm not sure.

Thank You Gordon

I appreciate Your opinion

[kriskros]

Hello All

Can anybody advise which lab in Europe can perform bond strength test with samples preparation with a use of proper adhesive? I have AMS2447-9 HVOF coating to test with min 70MPa bond strength test requirement.

I would be grateful for fast respond.