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Powdered Metal PM Sintered Steel Coating Surface Pretreatment

September 14, 2012

Q. I am looking to for a suitable surface pretreatment for coating a sintered steel part. The outer cam ring for a gerotor fuel pump. The coating will be PTFE or graphite/metal based solid film lubricant (haven't decided yet). Here is the recommended procedure I've found for both coating types:

"Degrease, grit blast, or grit blast and phosphate per MIL-PRF-16232 or TT-C-490 [from DLA] . Phosphate coating, although not mandatory, will enhance wear life and corrosion resistance and is highly recommended."

I know that a sintered part is very porous and that you need to seal the pores to provide a suitable surface. The sintering company that I'm working with does produce similar parts for another customer where the part is steam treated and eventually coated by some other vendor. This treatment helps to seal the pores and enhance corrosion resistance. They do not perform any subsequent processes after the steam treatment so we are unsure if anything else happens before the part is coated.

I assume that grit blasting a sintered part shouldn't be necessary since the surface is already uneven from the porosity. I also assume that we would want to avoid the grit blast anyway if we do the steam treatment.

Would phosphating be necessary or possible on a steam treated part?

I'm open to other suggestions.

Thanks.

Todd Wilson
Engineer - Jupiter, Florida