Metco 58NS CuNiIn Interface Problem

[johnrafiee]

Dear member 

I am looking for a way to reduce/eliminate interface separation/oxide/voiding/cracking in plasma sprayed Cu-Ni-In Metco 58 NS. 
During our initial spray a years ago, we did not found any of this defect. It keep building up time to time with the same parameter.


Spray parameter as follow

Gun Type : SinplexPro 90
Nozzle Diameter, Ø : 9 mm
Powder Injector Diameter, Ø : 1.8 mm
Powder Injector Angle : 90°
Current : 380 Amps
Primary Gas, Argon : 45 NLPM
Secondary Gas, Hydrogen : 2 NLPM
Powder Carrier Gas, Argon : 2 NLPM
Powder Feedrate : 40 g/min
Spreader/Suction Type : NL 16/1.2
Stirrer Speed : 60%
Spray Distance : 90mm
Rotation Speed : 50RPM
TCP Speed : 1000mm/min

Surface preparation were made with Grade 70 aluminum oxide with roughness around Ra 2-4um applied to Ti 6Al-4V substrate. Edge has been round off to ensure risk of edge seperation can be reduced.

The problem now we found an oxide, seperation and cracking at the coating near the interface on certain FOV. Can refer to my photo attachment

We had done many try and error such as etch after blast, preheat the substrate prior to spray, preheat the powder before spray but the problem still insist


For metallurgy preparation, 

The test panel was directly mounted using epoxy with vacuum impregnation. No sectioning was made

Planar grind with 180 SiC and Fine grind from 220 until 4000 SiC,
2 minutes 1um diamond polishing with Silk and 45 Second OP-S with Nap Cloth. 
No change to grinding and polishing parameter since day 1st of spray.


<a href="https://ibb.co/SBvPdFd"><img src="https://i.ibb.co/SBvPdFd/1-branch-cracking.jpg" alt="1-branch-cracking" border="0"></a>

<a href="https://ibb.co/ZWb1SQQ"><img src="https://i.ibb.co/FgdqXQQ/2-kicrocrack.jpg" alt="2-kicrocrack" border="0"></a>

<a href="https://ibb.co/MnqPvWT"><img src="https://i.ibb.co/mJQhj1s/6-crack.jpg" alt="6-crack" border="0"></a>

<a href="https://ibb.co/0j5K2RC"><img src="https://i.ibb.co/0j5K2RC/2-branch-cracking.jpg" alt="2-branch-cracking" border="0"></a>

<a href="https://ibb.co/SBvPdFd"><img src="https://i.ibb.co/SBvPdFd/1-branch-cracking.jpg" alt="1-branch-cracking" border="0"></a>

Appreciate all the opinion and idea. Thank you

[Lemster68]

Dear member 

I am looking for a way to reduce/eliminate interface separation/oxide/voiding/cracking in plasma sprayed Cu-Ni-In Metco 58 NS. 

Spray parameter as follow

TCP Speed : 1000mm/min

Do you mean 1000mm/Sec? 1000mm/Min would be exceptionally slow. Do you have crossing air jets into the plume to remove the soot/fines?

[johnrafiee]

Dear member 

I am looking for a way to reduce/eliminate interface separation/oxide/voiding/cracking in plasma sprayed Cu-Ni-In Metco 58 NS. 

Spray parameter as follow

TCP Speed : 1000mm/min

Do you mean 1000mm/Sec?  1000mm/Min would be exceptionally slow.  Do you have crossing air jets into the plume to remove the soot/fines?

Hi Lemster68

By the mean time I need to increase the TCP speed? Is there any speed recommendation?

Yes we apply the crossing airjets with 90mm distance.

[Vadim Verlotski]

Dear John,
judging by the photographs, critical compressive stresses (horizontal cracks) are formed in your coating. Such stresses can form if the substrate was too hot during spraying. To cool the substrate you need to increase the rotation speed of the part.

[Lemster68]

What is the part diameter?

[johnrafiee]

Dear John,
judging by the photographs, critical compressive stresses (horizontal cracks) are formed in your coating. Such stresses can form if the substrate was too hot during spraying. To cool the substrate you need to increase the rotation speed of the part.

Hi Vadim

We tried to increase the rotation speed to 60RPM but still produce similar result.  

Here I attach the latest micrograph from our early spray and the latest spray. We notice the oxide stringers are getting higher and thicker even tough we spray it on the same parameter. Fyi both sample was polished together for comparison

Regards
John        

[Vadim Verlotski]

Dear John,
there are no miracles in science and technology. If there are any changes in your coating, it means that the conditions of spraying have changed somehow, although you do not notice this. It is obvious to me that the changes are caused by overheating, since horizontal cracks have only that one explanation. Why overheating has come now, but before it was not, I cannot say for sure. There can be many reasons for this, ranging from clogged cooling nozzles, worn anode, problems with cooling water to changes in the particle size distribution of the powder. When dealing with thermal spraying, you cannot say: "I have not changed the parameters, therefore the quality of the coating must remain unchanged", since some parameters often change "by themselves" due to wear of components or unforeseen events.

[johnrafiee]

What is the part diameter?

Hi Lemster68

The part diameter was 0.75m

[johnrafiee]

Dear John,
there are no miracles in science and technology. If there are any changes in your coating, it means that the conditions of spraying have changed somehow, although you do not notice this. It is obvious to me that the changes are caused by overheating, since horizontal cracks have only that one explanation. Why overheating has come now, but before it was not, I cannot say for sure. There can be many reasons for this, ranging from clogged cooling nozzles, worn anode, problems with cooling water to changes in the particle size distribution of the powder. When dealing with thermal spraying, you cannot say: "I have not changed the parameters, therefore the quality of the coating must remain unchanged", since some parameters often change "by themselves" due to wear of components or unforeseen events.

Hi Vadim

Thank you for feedback. Until now there was no solution has been achieved although all parameter and hardware check and service already done. Will check with the Oerlikon about this

Regards
John

[ServiceTech]

Believe it or not, if the laboratory polishing method has changed the amount of oxide observed can be increased or decreased. Don't overlook this important aspect. In addition, .75 meters in diameter at 60 rpm is plenty fast enough. Check your sample specimen base material and grit blasting processes. If the base material is titanium, this can be part of the problem. Ensure the base material is polished before grit blasting to remove surface oxidation and then blast at a 45 degree angle to reduce grit entrapment.

[Taz]

Dear John,
judging by the photographs, critical compressive stresses (horizontal cracks) are formed in your coating. Such stresses can form if the substrate was too hot during spraying. To cool the substrate you need to increase the rotation speed of the part.

Hi Vadim,

I saw John replied that he used 90 mm crossjet cooling distance. Would it help to cool down the substrate by increasing the crossjet distance to 100 or 110 mm?

[Vadim Verlotski]

Hi Taz,
in order to enhance cooling, it is necessary not to increase the distance from the part to the compressed air nozzles, but, on the contrary, to decrease this distance. The closer the nozzle is to the part, the more efficient the cooling and the better the overspray is deflated. I always recommend no more than 50 mm, preferably 20-30 mm.

[johnrafiee]

Hi Taz,
in order to enhance cooling, it is necessary not to increase the distance from the part to the compressed air nozzles, but, on the contrary, to decrease this distance. The closer the nozzle is to the part, the more efficient the cooling and the better the overspray is deflated. I always recommend no more than 50 mm, preferably 20-30 mm.

Hi Vadim

Until now we did not solve this separation and cracking problem. I just realized the part didn't go trough pre heat with several passes of flame before feeding on with powder.
Can the pre heat helps to solve this issue?

[Vadim Verlotski]

Hi Taz,
in order to enhance cooling, it is necessary not to increase the distance from the part to the compressed air nozzles, but, on the contrary, to decrease this distance. The closer the nozzle is to the part, the more efficient the cooling and the better the overspray is deflated. I always recommend no more than 50 mm, preferably 20-30 mm.

Hi Vadim

Until now we did not solve this separation and cracking problem. I just realized the part didn't go trough pre heat with several passes of flame before feeding on with powder.
Can the pre heat helps to solve this issue?

Hi John,

preheating helps if vertical cracks (tensile stresses in the coating) appear in the coating after cooling. In your case, the cracks are clearly horizontal (compressive stresses in the coating). In the case of horizontal cracks in the coating, only intensive cooling of the part during the spraying process helps, and preheating can be harmful.

[johnrafiee]

Hi Taz,
in order to enhance cooling, it is necessary not to increase the distance from the part to the compressed air nozzles, but, on the contrary, to decrease this distance. The closer the nozzle is to the part, the more efficient the cooling and the better the overspray is deflated. I always recommend no more than 50 mm, preferably 20-30 mm.

Hi Vadim

Until now we did not solve this separation and cracking problem. I just realized the part didn't go trough pre heat with several passes of flame before feeding on with powder.
Can the pre heat helps to solve this issue?

Hi John,

preheating helps if vertical cracks (tensile stresses in the coating) appear in the coating after cooling. In your case, the cracks are clearly horizontal (compressive stresses in the coating). In the case of horizontal cracks in the coating, only intensive cooling of the part during the spraying process helps, and preheating can be harmful.

Hi Vadim

OEM recommend to preheat the part to 150 deg C with few pass of flame. So based on your opinion is still not advisable to pre heat the part?

[Vadim Verlotski]

Hi John,
In general, preheating is beneficial as it dries the surface of the part and thereby improves the adhesion of the coating. However, in the case when the cooling during spraying is insufficient, preheating excessively increases the temperature of the part, which leads to the formation of critical compressive stresses in the coating (your case!). If you can provide the parts with sufficient cooling power, then preheating will be beneficial, but in the case of low power cooling, preheating is harmful.

[johnrafiee]

Hi John,
In general, preheating is beneficial as it dries the surface of the part and thereby improves the adhesion of the coating. However, in the case when the cooling during spraying is insufficient, preheating excessively increases the temperature of the part, which leads to the formation of critical compressive stresses in the coating (your case!). If you can provide the parts with sufficient cooling power, then preheating will be beneficial, but in the case of low power cooling, preheating is harmful.

Hi Vadim

We just aware that the cracking is propagating over time. And few sources said historically this CuNiIn coating are prone to exhibit changes in interface separation over time. Thus the cracking issue we found originated from the interface separation. Any comments about this?

Best Regards
John

[Vadim Verlotski]

Hi John,
In general, preheating is beneficial as it dries the surface of the part and thereby improves the adhesion of the coating. However, in the case when the cooling during spraying is insufficient, preheating excessively increases the temperature of the part, which leads to the formation of critical compressive stresses in the coating (your case!). If you can provide the parts with sufficient cooling power, then preheating will be beneficial, but in the case of low power cooling, preheating is harmful.

Hi Vadim

We just aware that the cracking is propagating over time. And few sources said historically this CuNiIn coating are prone to exhibit changes in interface separation over time. Thus the cracking issue we found originated from the interface separation. Any comments about this?

Best Regards
John

Hi John,
If cracks appear a short time after coating, it indicates a high residual stress in the coating, leading to creep. If this time is long (weeks or more), then the cracks are more likely to develop due to corrosion.

[techmankpo]

Dear John,
in light of the photos, basic compressive anxieties (flat breaks) are framed in your covering. Such anxieties can shape in the event that the substrate was excessively hot during splashing. To cool the substrate you really want to speed up the part.