Metco 58NS coating coming off

[Christian_B]

Here's another problem from the real world which is driving us crazy:

- we have been spraying Metco 58NS for many years on a repair part (Inco 718 base material, thin sheet metal, coating sprayed w/o bond coat)

- since this week the coating comes off right after the process. The 1"-samples coated in the same run (including blasting) are perfect both in metallography and bond strength

- nothing changed in the whole set-up (cooling nozzles, robotic manipulation, process parameters, etc.)

Anyone an idea where to start the investigation ?

Thx in advance, Christian

[Vadim Verlotski]

Here's another problem from the real world which is driving us crazy:

- we have been spraying Metco 58NS for many years on a repair part (Inco 718 base material, thin sheet metal, coating sprayed w/o bond coat)

- since this week the coating comes off right after the process. The 1"-samples coated in the same run (including blasting) are perfect both in metallography and bond strength

- nothing changed in the whole set-up (cooling nozzles, robotic manipulation, process parameters, etc.)

Anyone an idea where to start the investigation ?

Thx in advance, Christian

Symptoms (direct coming off after coating) means that the residual stresses in the layer become too high. This problem is the problem of overheating and is often encountered with thin substrates in the case of small deviations in cooling or powder feed. Perhaps the pressure in the compressed air system has sunk, or does the powder feeder promote more material than usual? Maybe your component is a bit thinner than usual? Also unfavorable powder charge (some fine powder than usual) can be the reason for the stripping.
You can try to increase the speed of the component and the robot speed, which will help to reduce stresses in the layer.

[loriolo]

Hi Christian
As this powder has high copper contain, against nickel 37% that has higher melting point, is very difficult to have a good parameters setting, and as Powder OEM insert to much fines in order to win more money, this powder produces dense coatings with low porosity and low oxide contain, and is very hard to obtain a good parameter set, I had very good result using the powder M-958.54 from FST instead of Metco 58NS, some time you could obtain better result only changing the powder. You must perform an Almen strip test, in order to analyze if there are too much sharp stresses. In order to blow out fines prevent the oxidation of the coating, and to have better powder melting, you must use cooling jets even if you use F4 gun, I recommend you the following items to check:
Spray distance 92mm
Surface speed 50 M/min with 5 mm step
Powder rate 42 gr/min
Carrier gas pressure and flow must be adjusted according of how you see the powder jet into the plasma plume
Air jets 4,5 psi and cross jets 118 mm
Check torch geometry with accuracy and if you use thirystor power source remove about 40/50 amps

[Christian_B]

Dear all,

thanks for your advice. Actually we found to have a bad powder batch combined with fine dust in the blasting process (due to a defective blasting cabin filter). Now works fine.

regards, Christian