Hi Allen
Inconel 718 wire is a nickel chromium iron base alloy probably not too different to the old
traditional arc wire bond coat materials (Metco 470AW) so arc spray coating should have a pretty good and reliable bond. Not sure on claims for Tafa/Praxair HVOF bond strengths, but I quote from the first generation air cooled Metco Diamond jet process manual on Diamalloy 1006 (Inconel 718)
Quote:Diamalloy 1006 is a dense, well-bonded nickel/chromium/iron base coat. Typical coatings exhibit microhardness in the range Rc 29-34 and microhardness DPH300 320-380. The coatings are characterized by a dense (negligible porosity), high tensile bond strength (greater than 11000 psi (76 MPa) and a high thickness limitation (greater than 0.100" (2.5 mm). The Diamalloy 1006 coatings resemble a wrought superalloy in that they can be machined, milled, drilled and tapped. Excellent finishes (8-12 microinches aa) can be obtained by grinding
Yes, probably somewhat hyped up
Anyway, unless the coating bond strengths are not adequate for application ie the coatings are falling off or lifting in process or service, I think bond strengths are probably more a distraction away from your problem.
To be honest, before going down the road of HVOF parameter development, I think you need to first establish how good and consistent your dye penetrant test really is, and to evaluate your coatings using metallography and cross-reference to dye test results. I would certainly not recommend trying to optimise the HVOF process purely on dye penetrant testing alone.