BEHAVIOR OF APSED TBCS SUBJECTED TO COOLING MEDIA IN THERMAL CYCLE SYSTEMS

In this study, first, yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) with CoNiCrAlY bond coats both were fabricated on IN718 superalloy substrate, using air plasma spraying (APS) techniques. In order to understand the actual microstructural morphological behavior, phase stability, and thermal cycling behaviors of 8YSZ TBCs were characterized by field emission spectroscopy equipped scanning electron microscopy (FESEM), differential scanning calorimetry (DSC) and thermal cycling test. DSC results confirmed the basic reason of selecting the high cycling temperature. The crack initiation and propagation under thermal stresses due to temperature differences from maximum temperature of 1100∘C to cooling medium; here, air cooling and water quenching are used. Arising from either edges or corners it was observed serious problem which is restraining thermal cycling lifetime of TBCs, indicating failure mechanism is independent from operating parameters of thermal cycling test. However, in comparison to water-cooled thermal fatigue life, air-cooled thermal fatigue lifetime was 2.36 times better.