Appling The WC hard coating on Hard substrate

[behzadsaberi]

Hello sorry for my poor English
I recently have applied WC-17Co & WC-10Co-4Cr on hardened SPK substrates by HP-HVOF method, but during finishing stage the coats showed a lot of fine cracks and even delaminating. What are the reasons of??/
thanks for your recommendations.

[Vadim Verlotski]

Hello sorry for my poor English
I recently have applied WC-17Co & WC-10Co-4Cr on hardened SPK substrates by HP-HVOF method, but during finishing stage the coats showed a lot of fine cracks and even delaminating. What are the reasons of??/
thanks for your recommendations.

Hi behzadsaberi,

There may be two reasons for the formation of cracks in the coat (individually or both):
1. Overheating of the substrate during the spraying (> 200°C),
2. Too thick monolayer (layer in a single pass > 10 micrometers ).

If the part is small or have thin wall, then it is very easy to overheat. In this case, it is necessary to use a powerful cooling and reduce the spraying time (sprayed with breaks for cooling).
If the monolayers are too thick, you must increase the speed of the device with respect to parts (to increase the number of tour per minute).

[behzadsaberi]

Hello sorry for my poor English
I recently have applied WC-17Co & WC-10Co-4Cr on hardened SPK substrates by HP-HVOF method, but during finishing stage the coats showed a lot of fine cracks and even delaminating. What are the reasons of??/
thanks for your recommendations.

Hi behzadsaberi,

There may be two reasons for the formation of cracks in the coat (individually or both):
1. Overheating of the substrate during the spraying (> 200°C),
2. Too thick monolayer (layer in a single pass > 10 micrometers ).

If the part is small or have thin wall, then it is very easy to overheat. In this case, it is necessary to use a powerful cooling and reduce the spraying time (sprayed with breaks for cooling).
If the monolayers are too thick, you must increase the speed of the device with respect to parts (to increase the number of tour per minute).

Hi Vadim Verlotski
Thanks for your response
There are several notifications that i have to mention sooner:
1) two of the piece works that had been coated were capstan with about 290mm diameter and the rotation speeds were about 120 & 240 RPM respectively. Transverse speed was 10mm/s.
2) Temperature of all piece works were controlled during the spraying process and the Temperature never got above 150 degree.
3) Surfaces of the substrates were sandblasted and not greasy at all.
Vadim Verlotski your statements are totally true but I really suspect to material properties of the substrates, as I mentioned the own substrate was very hard (hardened SPK) before coating. So could the cause of the cracks and delaminating of the WC coat back to the material properties of the substrate Or any other factors that I have missed? if yes what could i do to resolve that.
thanks again for your Patience.

[Vadim Verlotski]

Hi behzadsaberi,
Hard material should not be a problem. The only difference is that the roughness after blasting possibly too low. After my feeling you have low transverse speed with too slow rotation speed. I would have taken a minimum of 500 RPM with a transverse speed of 30 mm/s.
Regards