Sample Failure
03-13-2018, 11:27 AM,
#1
Sample Failure
Hi! Team,
I have sprayed NiCr( METCO WOKA-11-60-1) as bond coat about 600 microns
and WcCoCr as top Coat (WOKA-3652) about 250 Microns. Please look at the attached Microscopic analysis. Can anyone please tell me the causes of failure.

Used Console: JP8000 (Liquid Kerosene) with Standard Parameters
Gun - TAFA 5220
each pass cool down upto50C.

Regards,
Krishz



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03-13-2018, 02:33 PM, (This post was last modified: 03-13-2018, 02:37 PM by Vadim Verlotski.)
#2
RE: Sample Failure
Hi Krishz,
There are, clearly, too high tensile stresses in your coating system. This is to be expected with this thick NiCr bondcoat. If you can not reduce the bondcoat thickness, you need to increase the movement speed (RPM). Cooling after each pass is not sufficient if too thick a layer (> 10 microns) is formed per pass. Only the faster movement helps.

Regards
Vadim
Reply
03-15-2018, 06:19 AM,
#3
RE: Sample Failure
(03-13-2018, 02:33 PM)Vadim Verlotski Wrote: Hi Krishz,
There are, clearly, too high tensile stresses in your coating system. This is to be expected with this thick NiCr bondcoat. If you can not reduce the bondcoat thickness, you need to increase the movement speed (RPM). Cooling after each pass is not sufficient if too thick a layer (> 10 microns) is formed per pass. Only the faster movement helps.

Regards
Vadim

Thanks, Vadim. You always help me to find the solutions and keep me learning new things each and every day.

Reply
04-05-2018, 05:57 PM,
#4
RE: Sample Failure
(03-13-2018, 11:27 AM)demionkrishan Wrote: Hi! Team,
I have sprayed NiCr( METCO WOKA-11-60-1) as bond coat about 600 microns
and WcCoCr as top Coat (WOKA-3652) about 250 Microns. Please look at the attached Microscopic analysis. Can anyone please tell me the causes of failure.

Used Console: JP8000 (Liquid Kerosene) with Standard Parameters
Gun - TAFA 5220
each pass cool down upto50C.

Regards,
Krishz

Apply cooling over the substrate, do not cool directly the coating, or, don`t use cooling, keep it under 180ÂșC, or apply a graded coating, when you get about 550 microns, apply a mixture of 50-50 of NiCr and the WCCoCr build 100 microns and the rest of WCCoCr, probably will help and you are going to reduce risk of cracks, there is a lot of papers that explain the benefits of graded coatings, and in other matter, i can see your substrate does not have enough roughness, if you blast it with a 60-80 grit will help with to reduce tensile stress through the anchoring, check the standard EN 13507.
Greetings and hope this help you.
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