Effects of Some Light Alloying Elements on the Oxidation Behavior of Ni-Cr based and Fe-based alloys during Air Plasma Spraying

In atmospheric plasma spray (APS), alloy powders are heated to melting state and accelerated to the substrate. The oxidation of the sprayed particles greatly affects the coating properties. It is generally known that the addition of chromium, silicon gives alloys better oxidation resistance in bulk materials. Carbon and boron are elements of strong affinity for oxygen, which has been used in steel making process as de-oxidants. Addition of those elements in thermal spray powder alloy is expected to protect the base alloys from oxidation during APS.

 The oxidation behavior Ni-Cr based and Fe-based alloy powders with Si, B and C additions during APS was investigated in this study. Analysis of chemical composition and phases of oxides in the in-flight particles and deposited coatings was carried out. The results show that the addition of Si, B and C to Ni-Cr based and Fe-based alloys reduced oxidation of the base alloys significantly; especially during the flying period at higher particles temperature. The preferential oxidation and subsequent vaporization of Si, B and C from the surface of the sprayed particles are believed to play a major role in reducing oxidation during APS process.