Comparison of oxidation behavior of NiCoCrAlY coating deposited by VPS and HVOF process

To reduce a detrimental complex oxide formation, the bond coatings in gas turbines have typically been using either VPS or HVOF process. In this paper, VPS and HVOF processes were applied using NiCoCrAlY+HfSi based powder to evaluate the oxidation behavior of bond coatings according to the coating process. Each coating sample was subjected to 50 times cyclic heat treatment that was maintained at 950°C for 23h, and then the weight changed was measured at 20 ℃ to evaluate the oxidation behavior. After the oxidation test, the coating layer was analyzed by XRD, SEM, and EDS. A faster weight gain was observed in the VPS coating than in the HVOF coating because the alumina particles produced during the initial formation of the HVOF coating inhibited oxidation and diffusion. The VPS coating maintained a stable state forming the dense and thick thermal growth oxide (TGO) layer until the middle stage in the oxidation test, but the HVOF coating showed a rapid weight loss after 10 cycles, unlike the VPS coating. For the HVOF coating to be satisfied as a substitute for the VPS coating, it is important to form a fine and uniform oxide distribution in the coating formation process.