High-Temperature Oxidation Behavior of Nano-structured CoNiCrAlY-YSZ Coatings Produced by HVOF Thermal Spray Technique

摘要

In this study the effects of adding yttria-stabilized zirconia (YSZ) reinforcement by mechanical milling method on the oxidation resistance of CoNiCrAlY coatings were investigated. For this purpose 0, 5, 10 and 15% YSZ were mixed with the commercial CoNiCrAlY powder and mechanically milled for 24 h in argon atmosphere. The high-velocity oxygen-fuel method was used for deposition of composite and commercial powders on Inconel 617 substrate. Both commercial and nano-structured coatings were oxidized at 1000 A degrees C for 100 h. Scanning electron microscopy together with energy-dispersive spectroscopy and X-ray diffraction analysis were used for analyzing the oxide scales formed on the coatings surface after oxidation process. The results showed that the porosity of nano-structured coatings was higher than that of the commercial coating, which was related to an undesirable morphology of the feedstock powders. The relatively high porosity of the nano-structured coatings caused the diffusion rate of oxygen into the coatings to be accelerated. On the other hand, a high Al supply due to a large amount of grain boundaries in nano-structured coatings facilitated the formation of an Al2O3 layer on coating's surface. The undesirable oxidation of splats in nano-structured coatings during spraying resulted in an increased oxidation rate of the coatings.