Corrosion Problem on HVOF Coating (DJ2600 Metco Gun)
01-06-2022, 09:00 AM,
#1
Corrosion Problem on HVOF Coating (DJ2600 Metco Gun)
Hi All;

I have corrosion problem on HVOF coating. I need your support please. 

We are using Oerlikon Multicoat system and the gun is DJ2600. 

Gasses are oxgyen and hydrogen. Powder is Metco 5847. Please see below informatin about powder. 

Nominal Chemistry
WC 10Co 4Cr
Nom. Particle Size Distr.(µm)
-53 +11

Primary Carbide Particle Size
Fine and Medium Size, Blend (TS Powders)
Range of Apparent Density (g/cm3)
2.9


The requirements are below and they are ok. 


Hardness is 900-1200 HV
Porosity must be under %1
Oxides must be under %1
There are no unmelts and cracks.

Before coating, we are applying the pre-heating and then blasted with white aluminum oxide. Size is 60 grit. Distance is 7 inch and pressure is 70 psi

We need to pass corrosion test. We coated the 4340 steel bar(200 KSI). Coupon diameter is 2.5 inch diameter and lenght is 5 inch. Coating thickness is 0.006" on surface. Spray distance is 11".

Uncoated end faces of cylindrical coupon and adjacent ¼” length of OD on both ends of coupon is sealed with sealant prior to the corrosion test.

Coupon is tested to 1000 hours (42 days) of Salt Fog exposure per ASTM B117 but we couldn't pass the corrosion test. We saw the corrosion after 35 days(maximum). 

We made a too much trial in a one year. We made the coupons with same parameters but some of them is resisting  only 10 or 15 days

I tried to upload coupon picture. You can see the small corrosion spot on the surface. Thank you very much for your attention.

https://ibb.co/kyQGnJn
Reply
01-06-2022, 10:05 AM,
#2
RE: Corrosion Problem on HVOF Coating (DJ2600 Metco Gun)
(01-06-2022, 09:00 AM)xxxxmgulkokan Wrote: Hi All;

I have corrosion problem on HVOF coating. I need your support please. 

We are using Oerlikon Multicoat system and the gun is DJ2600. 

Gasses are oxgyen and hydrogen. Powder is Metco 5847. Please see below informatin about powder. 

Nominal Chemistry
WC 10Co 4Cr
Nom. Particle Size Distr.(µm)
-53 +11

Primary Carbide Particle Size
Fine and Medium Size, Blend (TS Powders)
Range of Apparent Density (g/cm3)
2.9


The requirements are below and they are ok. 


Hardness is 900-1200 HV
Porosity must be under %1
Oxides must be under %1
There are no unmelts and cracks.

Before coating, we are applying the pre-heating and then blasted with white aluminum oxide. Size is 60 grit. Distance is 7 inch and pressure is 70 psi

We need to pass corrosion test. We coated the 4340 steel bar(200 KSI). Coupon diameter is 2.5 inch diameter and lenght is 5 inch. Coating thickness is 0.006" on surface. Spray distance is 11".

Uncoated end faces of cylindrical coupon and adjacent ¼” length of OD on both ends of coupon is sealed with sealant prior to the corrosion test.

Coupon is tested to 1000 hours (42 days) of Salt Fog exposure per ASTM B117 but we couldn't pass the corrosion test. We saw the corrosion after 35 days(maximum). 

We made a too much trial in a one year. We made the coupons with same parameters but some of them is resisting  only 10 or 15 days

I tried to upload coupon picture. You can see the small corrosion spot on the surface. Thank you very much for your attention.

https://ibb.co/kyQGnJn
Hi,
WC-Co-Cr and WC-Co coatings with a porosity of about 1%, in principle, are not corrosion-resistant, since they are permeable to water. In order for such a coating to become impermeable to aqueous solutions, it must either have a porosity below 0.1% or be impregnated with a polymer composition filling the porosity. Since it is impossible to obtain WC86Co10Cr4 with a porosity of less than 0.1% with the DJ2600 HVOF device, you only have the option with impregnation.
Reply
01-06-2022, 11:55 AM,
#3
RE: Corrosion Problem on HVOF Coating (DJ2600 Metco Gun)
(01-06-2022, 10:05 AM)Vadim Verlotski Wrote:
(01-06-2022, 09:00 AM)xxxxmgulkokan Wrote: Hi All;

I have corrosion problem on HVOF coating. I need your support please. 

We are using Oerlikon Multicoat system and the gun is DJ2600. 

Gasses are oxgyen and hydrogen. Powder is Metco 5847. Please see below informatin about powder. 

Nominal Chemistry
WC 10Co 4Cr
Nom. Particle Size Distr.(µm)
-53 +11

Primary Carbide Particle Size
Fine and Medium Size, Blend (TS Powders)
Range of Apparent Density (g/cm3)
2.9


The requirements are below and they are ok. 


Hardness is 900-1200 HV
Porosity must be under %1
Oxides must be under %1
There are no unmelts and cracks.

Before coating, we are applying the pre-heating and then blasted with white aluminum oxide. Size is 60 grit. Distance is 7 inch and pressure is 70 psi

We need to pass corrosion test. We coated the 4340 steel bar(200 KSI). Coupon diameter is 2.5 inch diameter and lenght is 5 inch. Coating thickness is 0.006" on surface. Spray distance is 11".

Uncoated end faces of cylindrical coupon and adjacent ¼” length of OD on both ends of coupon is sealed with sealant prior to the corrosion test.

Coupon is tested to 1000 hours (42 days) of Salt Fog exposure per ASTM B117 but we couldn't pass the corrosion test. We saw the corrosion after 35 days(maximum). 

We made a too much trial in a one year. We made the coupons with same parameters but some of them is resisting  only 10 or 15 days

I tried to upload coupon picture. You can see the small corrosion spot on the surface. Thank you very much for your attention.

https://ibb.co/kyQGnJn
Hi,
WC-Co-Cr and WC-Co coatings with a porosity of about 1%, in principle, are not corrosion-resistant, since they are permeable to water. In order for such a coating to become impermeable to aqueous solutions, it must either have a porosity below 0.1% or be impregnated with a polymer composition filling the porosity. Since it is impossible to obtain WC86Co10Cr4 with a porosity of less than 0.1% with the DJ2600 HVOF device, you only have the option with impregnation.
I am very pleased about your information. We try to fix this problem but on the metco web site, Metco 5847 powder has a corrosion resistant. Please see below link.

https://mymetco.oerlikon.com/en-us/product/metco5847oduct/metco5847

About the polymer composition; the customer don't give the permission using it for steel substrates but we can use it for only aluminum substrate. Customer suggest that we can use the Metcoseal AP after spraying on the coating

https://mymetco.oerlikon.com/en-us/product/metcosealap
Reply
01-06-2022, 12:51 PM,
#4
RE: Corrosion Problem on HVOF Coating (DJ2600 Metco Gun)
Advertising always exaggerates the value of the product. Yes, WC-Co-Cr coatings themselves are corrosion resistant, but it is not the coating that corrodes, but the substrate underneath. In this sense, it is more correct to speak not about the corrosion resistance of the coating, but about its permeability to water. By the way, absolutely the same applies to traditional hard chromium coatings, which also do not corrode themselves, but pass water to the substrate through a network of microcracks.

As for impregnations for coatings, there are quite a few of them. Before choosing a specific product, it is worth trying it on a specific coating. In this matter, one should focus on the size and number of pores: the less the porosity of the coating, the less viscous the impregnating liquid should be.
In the case of coatings with a porosity of less than 1%, not only specialized impregnations, but also "home" agents in the form of various oils, for example, linseed oil, are good against corrosion of the substrate.
Reply




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