max. substrate hardness for HVOF

Posted by John Groweg ( on 21:40:19 02/03/06

I work in the oilfield industry. We have an application where we are applying Cu-Ni-In HVOF 0.25 mm thick for corrosion protection. The substrate is a custom Austenitic Manganese Chrome stainless steel (140KSI 0.2% min yield) which has a Brinell hardness range of 300-415. We want to shot peen the substrate with S-780 shot before HVOF to increase fatigue life of the substrate. Shot peening will significantly increase surface hardness.
What is the maximum practical surface hardness of the substrate to insure that grit blasting will be adequate for proper bond strength of the HVOF? We don't want the surface to be so hard that grit blasting before HVOF is ineffective. At the same time, the part in question is subjected cyclic bending fatigue in corrosive media and has a history of corrosion fatigue failure. We need the shot peening to increase fatigue life and HVOF for corrosion protection.
Fatigue/corrosion testing has shown the HVOF to be superior other coating options.

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