loss on nickel during hvof process
09-15-2009, 04:22 PM,
Question  loss on nickel during hvof process
I am currently trying to determine what powder has been used to spray an HVOF coated surface. We believe the powder to be a Chromium-Carbide/Nickel-Chrome, specifically Diamalloy 3004. Three methods have now been employed to determine composition (SEM, XRD and XPS) and all have come up showing too high of a weight percentage for chromium, but too low for Nickel. During the HVOF process is it reasonable to assume that Nickel is lost more rapidly that Chromium? Does anyone know of any studies/articles discussing this?
09-16-2009, 03:19 PM,
RE: loss on nickel during hvof process
Hi twortham

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No experience with chemical analysis of these coatings before or after HVOF spraying, but I hope the following comments will be food for thought.

Diamalloy 3004 is a blended powder (75/25 chromium carbide/nickel chromium). Assuming for a moment your coating is Diamalloy 3004, then the fact that this powder product is a blend could lead to variation in composition from powder to coating and heterogeneous variation within coating from:
* uneven blend, powder settlement, classification effects during spraying
* powder constituents having different deposit efficiencies
* elemental burn off during spraying

Chromium carbide/nickel chromium powders can come in a variety of compositions like 80/20 and also in different forms like clad and sintered. Clad and sintered products I would expect to to show a more consistent coating composition compared to a blend.

Coating metallography of Diamalloy 3004 and other blended chromium carbide/nickel chromium coatings tend to have fairly distinctive microstructure compared to that of coatings from clad and sintered powders.

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