Hot corrosion behavior of intermixed layered LTA/YSZ thermal barrier coatings

Abstract

In present work a unique combination of hybridized intermixed five layered coatings structure is developed by using Arc plasma spray method. A Lanthanum-Titanium-Aluminum Oxide (LaTi2Al9O19) that is LTA powder is used as a ceramic top coat material along with YSZ. A bond coat of nickel dominant NiCrAlY having thickness of 90 µm (µm) is applied on the substrate Inconel 718 post shot blasting. A preceding layer of YSZ with 50% and remaining 50% of 50 µm bond coat is sprayed. After that a layer of YSZ having thickness of 100 µm is applied. Then a layer of 50 µm thickness having 50% YSZ and 50% LTA is applied. LTA layer of thickness 100 µm is applied at the end. Cyclic and isothermal hot corrosion is performed using salts Na2SO4 & NaCl in 3:1 mass proportion at 900 °C. The mass increment by as-sprayed intermixed coatings is less than 0.05 mg/cm2 and it is 0.02 mg/cm2 for annealed coating. An annealed intermixed coating shows negligible mass increment and has survived upto 100 h in case of isothermal hot corrosion. In case of cyclic hot corrosion annealed intermixed coatings shown no mass increment and is survived till 70 h. Mass increment of as-sprayed intermixed coatings is less than 0.05 mg/cm2 but after 50 h severe spallation of coating occurred. The coating surface morphology is evaluated through field emission scanning electron microscopy (FESEM) and x-ray (XRD) diffraction.