I currently spray an Aluminum Bronze powder using an Argon/Helium gas mixture. I have been experimenting with using only Argon but I am not able to get the same quality of coating. I have tried different parameters for the Argon that would give it equivalent properties to the mixture: equivalent enthalpy, mass flow rate, temperature, gun voltage, etc. No matter what I try, my microstructure is poor quality and my bond strength is low. There are really only two trends I've noticed in the microstructure. If I keep the Argon flow rate under 200 scfh I get many oxides and if it's over 200 scfh I get a good microstructure but I also get some separation at the interface. Both of these situations lead to the poor bond strength. To address the separation, I have tried improved surface prep, decreased spray distance, and more surface preheat, but none of that has worked.
So, my questions are: