Cr2O3 chromium oxide spray problems by Plasma

[anne]

Hello everyone,

I've tried to spray Cr2O3 coating by Plasma (F4MB-XL) and i've got a many problems. I don't have a reference parameters for that material (AMPERIT 707.092 (-75/25) so I based on the another ref.param. for finer granulation.
Parameters:
630A, AR: 43nlpm, H2: 10-13NLPM,
SD:~100-120mm, Vgun-1000mm/s, step:4mm, nozzle 6mm, powder inj&distance 1,5, 6mm,
PFR-45-55g/min. Power of the gun is near the maximum in the range between 48-49kW. After spraying the coating is very dark and inhomogeneous, the roughness is very high about 10-11Ra. On the surface is many spits (non molten powder?). Thickness gain: 15-17um. The metallographic analysis don't looks so bad as the surface, but a high porosity is visible (15%, which may be the result of poor preparation). And the last problem is that during spraying is a huge smoke! But it is prabobly effect of high content of the hydrogen in plasma gases. PLEASE for advice and guidance.

[Vadim Verlotski]

Hello everyone,

I've tried to spray Cr2O3 coating by Plasma (F4MB-XL) and i've got a many problems. I don't have a reference parameters for that material (AMPERIT 707.092 (-75/25) so I based on the another ref.param. for finer granulation.
Parameters:
630A, AR: 43nlpm, H2: 10-13NLPM,
SD:~100-120mm, Vgun-1000mm/s, step:4mm, nozzle 6mm, powder inj&distance 1,5, 6mm,
PFR-45-55g/min. Power of the gun is near the maximum in the range between 48-49kW. After spraying the coating is very dark and inhomogeneous, the roughness is very high about 10-11Ra. On the surface is many spits (non molten powder?). Thickness gain: 15-17um. The metallographic analysis don't looks so bad as the surface, but a high porosity is visible (15%, which may be the result of poor preparation). And the last problem is that during spraying is a huge smoke! But it is prabobly effect of high content of the hydrogen in plasma gases. PLEASE for advice and guidance.

Amperit 707,092 is too coarse. Such large particles do not melt completely: the surface of the particles is too hot (problems with smoke - CrO3 and black color - CrO), but the core remains solid (problem with high porosity).

[anne]

Hello everyone,

I've tried to spray Cr2O3 coating by Plasma (F4MB-XL) and i've got a many problems. I don't have a reference parameters for that material (AMPERIT 707.092 (-75/25) so I based on the another ref.param. for finer granulation.
Parameters:
630A, AR: 43nlpm, H2: 10-13NLPM,
SD:~100-120mm, Vgun-1000mm/s, step:4mm, nozzle 6mm, powder inj&distance 1,5, 6mm,
PFR-45-55g/min. Power of the gun is near the maximum in the range between 48-49kW. After spraying the coating is very dark and inhomogeneous, the roughness is very high about 10-11Ra. On the surface is many spits (non molten powder?). Thickness gain: 15-17um. The metallographic analysis don't looks so bad as the surface, but a high porosity is visible (15%, which may be the result of poor preparation). And the last problem is that during spraying is a huge smoke! But it is prabobly effect of high content of the hydrogen in plasma gases. PLEASE for advice and guidance.

Amperit 707,092 is too coarse. Such large particles do not melt completely: the surface of the particles is too hot (problems with smoke - CrO3 and black color - CrO), but the core remains solid (problem with high porosity).

Thanks a lot, i have the same suppositions.. but how i can solve this problem with that powder? Any ideas?

[Vadim Verlotski]

Thanks a lot, i have the same suppositions.. but how i can solve this problem with that powder? Any ideas?

With this powder you can not do anything except fine milling. But is simple to buy a finished finer powder (Amperit 707.001, 707,072 or similar).

[anne]

Thanks a lot, i have the same suppositions.. but how i can solve this problem with that powder? Any ideas?

With this powder you can not do anything except fine milling. But is simple to buy a finished finer powder (Amperit 707.001, 707,072 or similar).

Thats a simple method, but I have on the stock a lot of powder .092

[loriolo]

Hi Anne
There are Cr2O3 coarser powder, for example 90/25 µm and I obtained a good result, what kind of Powder feeder do you use, maybe the problem could be there, If there are to smoke during spray, you must check the powder for to high fines particles contain

[anne]

Hi Anne
There are Cr2O3 coarser powder, for example 90/25 µm and I obtained a good result, what kind of Powder feeder do you use, maybe the problem could be there, If there are to smoke during spray, you must check the powder for to high fines particles contain

All system is new, from Oerlikon, Twin-140 Powder Feeder. Today i'm going to spray with lower powder feeding.

[anne]

hello again, i really need your help.
The photo above presents the results of plasma spraying of finer powder (22/5um) using reference parameters but not completly...(the power limitation <48kW of the F4MB gun don't allow me set up ref. parameters, showed below:
630A->600A, Ar 38NLPM, H2 13->12,5nlpm, PFR 50->40g/min, SD 100mm, Vgun 1000mm/sec. Using these parameter i obtained 72V, and the power 48kW.

I obtained 20um per pass.

Coating delamination may be results of too low powder particle velocity, but how to change that? By decreasing hydrogen flow and increasing amperage? It's a good way? May I should decrease powder feeding? I do not want to lose a lot of material, but I am aware of how much before me.
It's hard situation for me because i don't have any support, and the plasma is not my black horse, or not yet

If someone sprayed the chromium oxide i have one more qusetion, what color have you obtained?

Reagrds

[Gordon]

Hi Anne

Not sure if gun parameters are optimal or not, but thickness per pass is too high and will be the primary reason for the poor microstucture. I would aim for less than 5um per pass, which should give you a big improvement.

The as-sprayed colour should be a dark grey on areas that are clean. Areas that may collect fine over-spray material will look darker or even have a green tinge.

Hope that helps and good luck.

[anne]

Thank you for the advice. I'm working on it tommorow by decreasing PFR. I hope it will help.