The Effect of Low Pressure Plasma Sprayed Parameters on the Microstructure of NiCoCrAlY Coatings and Comparsion with HVOF Process

To improve the efficiency and power output of turbine engines, the turbine inlet temperature should be increased which requires higher oxidation resistance of MCrAlY coatings. Moreover, the oxidation resistance of the MCrAlY coating depends on the chemical composition and coating’s microstructure, which can be improved by optimizing the parameters of coating process. In this study the parameters of LPPS process on the microstructure of NiCoCrAlY coating is evaluated and compared with the microstructure of NiCoCrAlY coating applied by the HVOF method. Thus, microstructure, phase composition and elemental analysis of the coatings are characterized by optical and field emission scanning electron microscopy (FESEM), X-ray diffractometer (XRD) and energy dispersive spectroscopy (EDS), respectively. The results reveal that the optimum microstructure of the coating with minimum porosity, non-melted particles and oxide phases was obtained at the highest temperature and particle’s velocity impact to the substrate’s surface. Hence, the optimized values for Ar and H2 flow rate (75 and 16 SLPM, respectively), and the current of 650 A at a spray distance of 12 cm has been optimized for for maximum amount of remaining particles at maximum speed in plasma jet. In addition, EDS and XRD analysis show that the NiCoCrAlY coating contains continuous γ nickel rich solid solution with dispersed β- (Ni, Co) Al phases and negligible ratio of oxide phase.