HVOF T800 Tensile Bond Strength issue

[wgg237]

Hi guys,

We are developing HVOF T800 with JP8000 (kerosene/O2). Currently, we just got a good coating microstructure(porosity, oxides, unmelted good), but faced a low TBS issue (Only Avg.~5000psi, far away from the target value 8500 psi. Cohesive failure in coating), as well as micro hardness of coating (Avg. 640 HV0.3, low than target value: 675). We had pre heating prior to coat spraying.

Appreciate your good ideas & experiences to share, Thanks!

[Vadim Verlotski]

Hi guys,

We are developing HVOF T800 with JP8000 (kerosene/O2). Currently, we just got a good coating microstructure(porosity, oxides, unmelted good), but faced a low TBS issue (Only Avg.~5000psi, far away from the target value 8500 psi. Cohesive failure in coating), as well as micro hardness of coating (Avg. 640 HV0.3, low than target value: 675). We had pre heating prior to coat spraying.

Appreciate your good ideas & experiences to share, Thanks!

Attached is metallographic photo of coating at 200X...

Hi,

When heating the substrate it may be oxidized and it reduces adhesion. Furthermore, you monolayer thickness is approximately 10 micrometers - a very much. Then thicker a monolayer, the higher the residual stresses in the coating and thus lower bond strength with the substrate. Try to increase the speed of movement of the workpiece surface (RPM) twice, at 5 micrometers thickness of the monolayer reduced stress significantly.

Regards

[wgg237]

Hi guys,

We are developing HVOF T800 with JP8000 (kerosene/O2). Currently, we just got a good coating microstructure(porosity, oxides, unmelted good), but faced a low TBS issue (Only Avg.~5000psi, far away from the target value 8500 psi. Cohesive failure in coating), as well as micro hardness of coating (Avg. 640 HV0.3, low than target value: 675). We had pre heating prior to coat spraying.

Appreciate your good ideas & experiences to share, Thanks!

Attached is metallographic photo of coating at 200X...

Hi,

When heating the substrate it may be oxidized and it reduces adhesion. Furthermore, you monolayer thickness is approximately 10 micrometers - a very much. Then thicker a monolayer, the higher the residual stresses in the coating and thus lower bond strength with the substrate. Try to increase the speed of movement of the workpiece surface (RPM) twice, at 5 micrometers thickness of the monolayer reduced stress significantly.

Regards

Thanks for your guidance... It seems more reasonable... Will let you know the tends after get the trial result.

[Sail L]

Dear all

I have the same problem recently (same equipment and coating requirement)
I tried decrease the deposit rate to 0.0002"/ pass with increase the linear speed but still fail.
And it's found that compare to higher deposit rate (0.0050"/ pass), lower rate seems no significant improvement and inconsistent with theory.
Is it possible that the problem is caused equipment ? (leak, powder feed type, etc...) (The device was recently calibrated.)
We use 3-way splitter to feed to gun with 1 powder feeder, will it affect the consistency of powder feeding ?

Thank you