Matrix cohesion problem of WC CoCr

[sams5313]

Coating parameter

1. Spray machine : Orelikon mecto DJ 2700
2. Gas flow
⓵ Oxygen :　40FMR / 150psi
⓶ FUEL(LPG) : 36FMR / 105psi
⓷ Air : 47FMR/ 105psi
3. Stand off : 230 mm
4. Powder feed rate : 40 g/min
5. Gun traverse speed : 100 cm/min
6. Test piece hold : Φ220
7. Test piece hold RPM : 490 RPM
8. Powder : WOKA3652 (WC10Co4Cr)
9. Test poece size : 15mm * 12mm * 4mm

Q: Coating conditions of sample 1 and sample2 are the same.
But the results(matrix cohesion) are different.
what is the reason?

[Lemster68]

I can't really tell you for two reasons: 1. I don't know and 2. You are not specifically stating what the two results were. Regarding the second, I think that might apply to everyone on this forum. Your RPM and traverse seem totally random, though. With that diameter and a surface speed of 60 M/Min I calculate 87 RPM with a 7.24 mm/sec traverse speed will give you an increment of 5 mm. With your RPM and speed I believe your increment will be 2.04 mm.

[loriolo]

Hi Sam
Remember that for HVOF applications, in order to have a correct coating deposition, and minimal coating stresses, the piece peripheral speed must be about 120 m/minute and gun traverse about 4 mm/ revolution, with old HVOV systems, especially the ones that use gas mix is normally that you could have a very stressed coating and low cohesion coating, something better are the coatings with HVOF liquid kerosene, but the best is the new HP HVOF that use O2 / Ethanol.