Recomended bond coat for Metco 81 VFNS top coat

[achmadarifudinh]

Hello guys, maybe u any advises about my case

Iam get a gas turbine part shroud in 3rd stage. the base material is x-45 closed to fsx-414, this part is urgently.

for the existing coating is to thicker, about 1000 micron with HVOF spray. so i will do coating same with existing thickness. my HVOF machine in trouble, so i just have air plasma spray.

im just try with metco 81 vfns to get smooth result. but the bonding strenght is not good.

Maybe any advises, like get a bond coat powder before i apply metco 81 vfns as top coat or any method to get good bonding strenght ???

Thanks full guys.
Regards.

Achmad Arifudin H

[demionkrishan]

Hi! Achmad,
As i know you can use this powder for HVOF or APS spray but maximum coating thickness limit is only 400-500 Microns and after that you will loose your bond strength / More porosity will apper
Mainly for shrouds, Most of the OEM recommendation for hard facing is up to 3-5 thou max or if your customer required abradable coating you can use bond coat and top coat to
receive 1000 microns thickness.

Note: I have done 81VF up to not more than 500 microns, If you want me to check your parameters, let me know your Console , gun and Spray parameters so i can understand
is something wrong there...

My recommendation here is
1. Weld build up your shroud surface 900 microns and 200 microns machining and apply 300 microns 81VF is better option
or
2. Use Metco 450 NS as bond coat and 410 NS as Top Coat ( Note: i have achieve up to 650 Microns , Bond coat 200 Microns bond and 450 Microns)
hope you can achieve
or
3. Abradable coating

Regards,
Demion Krishan Francis

[loriolo]

Hi Hachmad
The powder Chromium Carbide/Nickel/Chrome 75/20/5 you want to use is the same of FST K-855.21 and is used in high temperature conditions, so Ni5Al is not good as intermediate or bond coat coating, and 81VF is used for oxidation and corrosive media at high temperature up to 980 °C, if you use it for coating in turbine parts, so the coating system application and material must meet required customer specification, the maximum thickness for Metco 81 VF or FST K-855.21 is < 0.5mm, and bond strength of about 20,4 MPa, so if the final coating thikness is up to 05 mm, you must use an intermediate material if customer specification is not mandatory, otherwise you can use Ni20Cr (FST M-301.33) which bond strength is 26,8 and maximum thickness < 0,6 mm, and if you need more than 1 mm coating thickness, you could use a powder like NiCr5Al (FST M307.93 or Metco 443), that is a bond coat for high temperature application but with a little lower temperature limit (840 °c instead of 980), with a bond strength of about 32 MPa and a maximum thickness of about 2,5 mm

[achmadarifudinh]

Hi! Achmad,
As i know you can use this powder for HVOF or APS spray but maximum coating thickness limit is only 400-500 Microns and after that you will loose your bond strength / More porosity will apper
Mainly for shrouds, Most of the OEM recommendation for hard facing is up to 3-5 thou max or if your customer required abradable coating you can use bond coat and top coat to
receive 1000 microns thickness.

Note: I have done 81VF up to not more than 500 microns, If you want me to check your parameters, let me know your Console , gun and Spray parameters so i can understand
is something wrong there...

My recommendation here is
1. Weld build up your shroud surface 900 microns and 200 microns machining and apply 300 microns 81VF is better option
or
2. Use Metco 450 NS as bond coat and 410 NS as Top Coat ( Note: i have achieve up to 650 Microns , Bond coat 200 Microns bond and 450 Microns)
hope you can achieve
or
3. Abradable coating

Regards,
Demion Krishan Francis

Wow much knowledge i get from your information sir, thanks.

From the technical sheet metco 450 ns, i will used it "Salvage and build-up for restoration", "oxidizing atmosphere resistance below 800c". In 3rd shroud the temperature operation isnt up to 500c. I think this is my considered for this powder.

I will spray 400 - 500 micron for metco 450ns. Used 9MC, 9MP, and 9 MB gun.

Maybe u can advised the parameter operation like argon pressure, volt, and ampere value for get the best quality.

Thanks, so much Sir Francis
Regards.

Achmad Arifudin H

[demionkrishan]

Achmad,

See the attachment for parameters
   

[Lars.Patrick]

Has anyone ever used 81VFNS WITHOUT a bond coat?

We get tensile results in the 5,000 psi range with no bond coat.

[Vadim Verlotski]

Normally metco 81 vf-ns does not require a bondcoat and can be sprayed directly onto steels and nickel base alloys. But a bondcoat of Ni-Al can improve bond strength. Your adhesion of 5000 psi is too low for this coating.

[ServiceTech]

Has anyone ever used 81VFNS WITHOUT a bond coat?

We get tensile results in the 5,000 psi range with no bond coat.

A bond coating for 81VF-NS is not required until thicknesses reach upwards of .015".  I've been spraying this coating since 1986 and am not a fan of exceeding .012".  If a bond coating is required due to thickness issues, the typical bond coating per aero specs is usually Inconel 718.  Also, per aerospace specs, 5,000 psi is the minimum requirement.  

[Lars.Patrick]

Has anyone ever used 81VFNS WITHOUT a bond coat?

We get tensile results in the 5,000 psi range with no bond coat.

A bond coating for 81VF-NS is not required until thicknesses reach upwards of .015".  I've been spraying this coating since 1986 and am not a fan of exceeding .012".  If a bond coating is required due to thickness issues, the typical bond coating per aero specs is usually Inconel 718.  Also, per aerospace specs, 5,000 psi is the minimum requirement.  

Yes!

I reached out to an old spray buddy who said the same thing... 
I ended up spraying some tensile samples at different thicknesses to verify... indeed under 0.012" we got tensiles pulling ~7500 psi.

Thank you for the direction!

[ServiceTech]

Excellent news! Cheers my friend!!