HVOF T800 Tensile Bond Strength issue
03-03-2015, 09:36 AM, (This post was last modified: 03-04-2015, 06:44 AM by wgg237.)
#1
HVOF T800 Tensile Bond Strength issue
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!
Reply
03-03-2015, 11:03 AM,
#2
RE: HVOF T800 Tensile Bond Strength issue
(03-03-2015, 09:36 AM)wgg237 Wrote: 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
Reply
03-05-2015, 01:52 AM,
#3
RE: HVOF T800 Tensile Bond Strength issue
(03-03-2015, 11:03 AM)Vadim Verlotski Wrote:
(03-03-2015, 09:36 AM)wgg237 Wrote: 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.
Reply




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