Double Effect of Super-Hot Molten Droplets on the Formation of Oxide-Free Metal Droplets and Intersplat Bonding during APS using Deoxidizer-Containing Powders

With plasma spraying of metal coatings, severe oxidation leads to the coatings with high content of oxides inclusion and subsequently limited interlamellar bonding. Recently, we have proposed to design metal powders with certain deoxidizer to generate oxide-free molten droplets in ambient atmosphere by air plasma spraying. In this presentation, the synergistic effect of the generation of super-hot molten droplets on the formation of oxide-free metal droplets and intersplat bonding during APS using deoxidizer-containing powders will be examined. With Ni-based, Cu-based and Fe-based materials the boron can be used as deoxidizer, while with Al-containing alloys such MCrAlY and NiAl the carbon can be used as deoxidizer. It was confirmed that the generation of molten droplets higher than 2300oC fulfills the thermodynamic deoxidizing conditions. By examining the collected powder particles passing through plasma jet and splat morphology and splat-interface prepared by FIB, it was revealed that oxide-free molten metal droplets are achieved through using super-hot deoxidizer-containing powders. Furthermore, it will be shown that the sufficient metallurgical bonding is also achieved between splats within the coatings. Therefore, with spray metal powders design and generation of super-hot droplets, dense metal coatings with sufficient intersplat bonding and low oxide inclusions can be deposited by APS.