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  • 1.  Plasma Spray Gas Choice Problem

    Posted 04-13-2021 11:07

    I currently spray an Aluminum Bronze powder using an Argon/Helium gas mixture.  I have been experimenting with using only Argon but I am not able to get the same quality of coating.  I have tried different parameters for the Argon that would give it equivalent properties to the mixture: equivalent enthalpy, mass flow rate, temperature, gun voltage, etc. No matter what I try, my microstructure is poor quality and my bond strength is low. There are really only two trends I've noticed in the microstructure. If I keep the Argon flow rate under 200 scfh I get many oxides and if it's over 200 scfh I get a good microstructure but I also get some separation at the interface. Both of these situations lead to the poor bond strength. To address the separation, I have tried improved surface prep, decreased spray distance, and more surface preheat, but none of that has worked.

    So, my questions are:

    • Has anyone else sprayed a similar metal powder using only Argon and what settings worked for you?
    • Why does the addition of Helium create such a better coating? Why are my spray adjustments to account for its removal not adequate?
    • Does anyone know of some additional strategies to address the separation at the interface?

     

    Thank you,

    Kristen



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    Kristen Berube
    Product Development Engineer
    Turbocam
    Dover NH
    (603) 905-0461
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  • 2.  RE: Plasma Spray Gas Choice Problem

    Posted 04-14-2021 10:23
    Edited by Robert Miller 04-14-2021 10:46
    It would help if you could identify the hardware you spray with.  Aluminum bronze ought to be easy to melt and spray.
    Possibly, the powder carrier gas flow and powder injection port you're using, and maybe the nozzle, are not right for this powder with pure argon plasma gas, so the powder location and dwell time in the plasma jet aren't optimum.   I would first consult with the equipment supplier to get a starting parameter recommendation.

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    Robert Miller
    Materials Engineering Consultant
    R.A. Miller Materials Engineering
    Indianapolis IN
    (317) 698-5479
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  • 3.  RE: Plasma Spray Gas Choice Problem

    Posted 04-14-2021 12:35
    Thanks for the response!  So we actually had spoken with our equipment supplier very early on (2 years ago) about our intent to try Argon only at some point.  They recommended using subsonic hardware but they didn't seem to have a proven, tested configuration for this application.  We've actually tried several subsonic anode/cathode combinations, along with two different gas injectors and both internal/external powder injection.  I definitely will try reaching out to the supplier again though to see if some advances have been made in the past few years.  Thank you.

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    Kristen Berube
    Product Development Engineer
    Turbocam
    Dover NH
    (603) 905-0461
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  • 4.  RE: Plasma Spray Gas Choice Problem

    Posted 05-25-2021 14:11
    Since you are getting separation I would actually increase standoff. A few years ago we were applying a thin layer of a ferrous metal over a ceramic - so adhesion could be a challenge. Normal standoff that we initially tried was ~4" but we backed way out to 8" and even tried beyond that. Adhesion improved. I think we ended up still less than 8" but much farther out than we initially anticipated. The parameter and eqpt was subsonic (SG100 gun) Good luck! Do share what you end up with!

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    Joe Zanter
    R&D Engineer
    Thermal Spray Technologies
    Sun Prairie WI
    (608) 318-5077
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