Un-common surface pattern on coating failure
10-04-2016, 06:09 PM,
#1
Un-common surface pattern on coating failure
Hi All

Never seen this pattern on a roll, coated with W C Co Cr and ground finished

Used in a Non-ferrous Rolling mill, with appx 350 deg C sheet temperature and roll surface temperature of about 100 deg C

Coating was applied using HVOF and ground finished and super polished to 0.1-0.2 microns Ra

Can anyone help with the reason for this pattern on purported coating failure as per the customer?

My best guess was mechanical failure of the part; bearing seizure of roll whilst at work etc...

Thanks in Advance


Shantanu Newar


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Reply
10-05-2016, 08:39 AM,
#2
RE: Un-common surface pattern on coating failure
(10-04-2016, 06:09 PM)shantanu Wrote: Hi All

Never seen this pattern on a roll, coated with W C Co Cr and ground finished

Used in a Non-ferrous Rolling mill, with appx 350 deg C sheet temperature and roll surface temperature of about 100 deg C

Coating was applied using HVOF and ground finished and super polished to 0.1-0.2 microns Ra

Can anyone help with the reason for this pattern on purported coating failure as per the customer?

My best guess was mechanical failure of the part; bearing seizure of roll whilst at work etc...

Thanks in Advance


Shantanu Newar

Hi Shantanu,
The damage can have mechanical and thermal origin in the combination. 350°C is a critical temperature for WC-Co-Cr coatings on the steel. At this temperature (also locally at the surface) are created in the layer very high tensile stresses which can lead to cracking. The preheating of the roll on 150-200°C before the coating helps to prevent this damage mechanism.
Regards
Vadim
Reply
10-06-2016, 02:55 PM,
#3
RE: Un-common surface pattern on coating failure
Well, 350 deg C is not critical for WCCoCr yet.
And it is the temperature of the sheet, means coating surface temp is much lower.

What I suppose here is a grinding problem.
The coating application itself was great because most of the coating is still there despite a severe damage.
Grinding had overstressed the coating partially during one of the passes, then it has delaminated in service.

Best regards
Vig
Reply




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