High-temperature phase stability and TGO evolution in YSZ- LTA composite plasma-sprayed thermal barrier coatings

Abstract

Yttria stabilized zirconia (YSZ) is one of the most viable materials in thermal barrier coatings for its low thermal conductivity, high coefficient of thermal expansion and good thermal shock resistance. However, phase instability, rapid sintering and reduced strain tolerance limits its application. To address this gap, the present work aims at depositing lanthanum titanate aluminium (La0.83(La0.07Ti0.465Al0.465) O2.9) (LTA)-YSZ composite coatings on Inconel substrates using atmospheric plasma spray (APS) route to form ceramic nanocomposite coatings. LTA powder is synthesized via the co-precipitation method and the obtained powder is mixed with YSZ to form the composite feedstock in an equal weight ratio (50:50). The developed coatings are characterized for their phase constitution, microstructure, thermal diffusivity and thermal conductivity as per ASTM standards. The phase stability, mechanical response and thermally grown oxide (TGO) growth behaviour of the composite coatings following thermal exposure are also studied. The definitive separation of YSZ and LTA phases and mapping of lamellar structures and phase dispersion are clearly identified by scanning electron microscopy. The crystallographic structure of the composite coatings is determined using X-ray diffraction analysis. The results revealed that the incorporation of LTA phase improves the phase stability and TGO behaviour in YSZ based coatings. It is concluded that the YSZ-LTA composite coating demonstrates superior thermal barrier performance compared to YSZ coatings and can be used in thermal barrier applications.