Hi twortham

to the Surface Engineering Forum.
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.