Hardness increase in Chrome Ceramic Plasma Coating

[DMan]

Hello All

We coat Cr203 ceramic by plasma coating with oerlikon sinplex pro . 
Since past few weeks, the coating hardness has suddenly increased .
Although I have not made any changes to process parameters in coating, I am still wondering what may have suddenly caused this.
Can anyone guide me on particular factors which can cause sudden increase in hardness of ceramic.
Note : Power on gun, Feed Rate , gun distance are all same as before. No change in thickness/pass, powder flow rate same as before.
Warm regards
DMan

[Gordon]

Hi DMan

Increase in hardness of Cr203 ceramic will be due to an increase in coating density or reduction of porosity. This indicates parameters or powder have changed.

[Vadim Verlotski]

A sudden increase in the hardness of a ceramic coating can also occur due to a lack of cooling of the component during plasma spraying (failure of the cooling). The structure of the coating is coarsened (coarser crack network compared with a cooled layer) and the higher hardness is measured. However, this does not necessarily improve the layer quality.

[plasmajet1990]

Hello All

We coat Cr203 ceramic by plasma coating with oerlikon sinplex pro . 
Since past few weeks, the coating hardness has suddenly increased .
Although I have not made any changes to process parameters in coating, I am still wondering what may have suddenly caused this.
Can anyone guide me on particular factors which can cause sudden increase in hardness of ceramic.
Note : Power on gun, Feed Rate , gun distance are all same as before. No change in thickness/pass, powder flow rate same as before.
Warm regards
DMan

Hello,

Please check the hardness tester.

Ion

[DMan]

A sudden increase in the hardness of a ceramic coating can also occur due to a lack of cooling of the component during plasma spraying (failure of the cooling). The structure of the coating is coarsened (coarser crack network compared with a cooled layer) and the higher hardness is measured. However, this does not necessarily improve the layer quality.

Dear Vadim

Thanks again.
Initially I found that one of the Cross Air jets nozzle was blocked and so One nozzle was blowing full air and the other nozzle was throwing half the volume.
I am wondering if this could be one of the reasons for sudden increase in hardness.
Also, today found that the spraying distance for Oerlikon  Gun was 100 mm instead of 114 mm as specified by Oerlikon . Could be a factor also. . 

Spray distance wont be changed automatically since we use a robotic control with set parameters since beginning . So i still wonder what may have gone wrong suddenly . I was suspecting the cross air jets cooling..but doesnt seem so.

Await to hear you.
DMan

[Lemster68]

A sudden increase in the hardness of a ceramic coating can also occur due to a lack of cooling of the component during plasma spraying (failure of the cooling). The structure of the coating is coarsened (coarser crack network compared with a cooled layer) and the higher hardness is measured. However, this does not necessarily improve the layer quality.

Dear Vadim

Thanks again.
Initially I found that one of the Cross Air jets nozzle was blocked and so One nozzle was blowing full air and the other nozzle was throwing half the volume.
I am wondering if this could be one of the reasons for sudden increase in hardness.


Await to hear you.
DMan

That is pretty much what Vadim had already suggested to you.

[DMan]

Dear All

Since I am looking at number of factors, I have to confirm one thing. What is the ideal coating thickness of Cr203 ceramic ?
I am trying to corelate if excess coating thickness will makes the coating more dense resulting in increase in hardness. I generally keep it around 200-250 microns Top coat, but of late in some cases i have made 300 microns coating. Could this be a factor too.
Thanks in advance
Dman